Introduction

The use of personal care products, especially protective ultraviolet agents, has witnessed an unprecedented global rise in protecting the human skin from various health risk concerns due to increasing climate change. However, the ecological and environmental consequences of using these agents are often overlooked, which could indirectly cause harmful threats to the ecosystem, especially marine life (Anand et al. 2022a). A general understanding of the measure of the lifetime exposure of human beings as it relates to human health from birth to death is defined by the exposome (Ajibade et al. 2021). Interestingly, the most significant kind of exposure from a list of diet, lifestyle, and occupational hazards is the exposure to ultraviolet radiation emanating mainly from the sun and a few other less significant artificial sources such as tanning beds, halogen and incandescent lights, lasers, and mercury vapor lightings predominant in stadia and school gymnasia. Excessive anthropogenic pollution has enhanced the continuous depletion of the stratospheric ozone layer globally, thereby subjecting all biotic and abiotic elements to harmful ultraviolet radiation in the ecosystem (Ali and Khan 2017).

Among other radiations, sunlight emits ultraviolet, corresponding to the wavelength range of 100–400 nm, visible light, with a wavelength from 400 to 700 nm, and infrared radiation, falling in the wavelength range of 700 nm to 1 mm. Based on their biological effects, the ultraviolet component of the electromagnetic spectrum is split into three categories: UV-A radiation corresponding to long wave 320–400 nm, UV-B radiation falling in the mid-wave 290–320 nm and UV-C radiation the short wave 200–290 nm (Katiyar 2016). UV-A and UV-B have photobiologic characteristics that change over time. Even though the sun produces a lot of ultraviolet radiation, only 5% of it reaches the earth's surface in the ultraviolet spectrum, corresponding to 96.65% UV-A and 3.35% UV-B, with UV-C virtually undetectable (Rünger et al. 2012). Indeed, the stratospheric ozone layer generally filters high-energy UV-C light. Terrestrial organisms constantly face exposure not only to natural environmental factors like ultraviolet radiation but also to pollutants originating from human activities. The skin is the body's largest organ and plays a crucial role as the primary interface with the external environment. It is responsible for protecting us from physical and chemical influences that could potentially impact the body's various functions. The skin acts as a metabolic defensive barrier, preventing ultraviolet radiation from penetrating deeper tissues (Patel et al. 2021). However, chronic exposure to solar ultraviolet radiation, especially UV-A and UV-B, generates oxidative stress and induces skin damage. UV-B radiation has the ability to traverse the entire epidermis layer and reach the dermis compartment of the human skin, as represented in Fig. 1 (Romanhole et al. 2015; WHO Newsroom 2016).

Fig. 1
figure 1

Penetration of the skin by ultraviolet radiation of different wavelengths. The ultraviolet radiation spectrum that reaches the earth’s surface is categorized into medium wavelength (UV-B) and long wavelength (UV-A); 95% of this total ultraviolet radiation is UV-A. The biological activity of UV categories, i.e., the damaging effect on the skin is largely based on their wavelength such that the shorter the wavelength, the more harmful the radiation on the skin. Despite its high level of biological activity, the UV-B does not penetrate beyond the superficial skin layers (epidermal cell components, e.g., proteins or DNA), thus responsible for the delayed tanning and burning effects. Besides, most UV-B is filtered or absorbed by the ozone and other components of the atmosphere as sunlight passes through the atmosphere. The UV-A, however, has the capability to penetrate deeper into the skin, reaching the basal layer of the epidermis and even extending to the dermal fibroblasts, thus responsible for the immediate tanning effect while contributing to skin aging and wrinkling. Additionally, natural substances (phytochemicals) protect the skin from the damaging effects of ultraviolet radiation (green arrow). The image was formed with the assistance of https://biorender.com

Full size image

This photooxidative stress leads to sunburn, erythema, edema, and phototoxic reactions, such as photoallergy, photosensitivity, photoaging, and photocarcinogenesis, via numerous pathways (Sardoiwala et al. 2018). On the other hand, it is well documented that the effects of ultraviolet radiation on the skin can indirectly affect the skin microbiota (Farghali et al. 2022). Ultraviolet radiation has been shown to alter the composition and activity of the microbiota, as well as modulate cellular response and immunological function (Patra et al. 2019).

Moreover, photoprotection is a biological mechanism that aids organisms in co** with the cellular and molecular damage induced by sun radiation. Physical ultraviolet filters, such as sunglasses and sun clothing, and chemical ultraviolet filters, such as sunscreen lotions, are both useful, but they do not offer comprehensive protection (D’Orazio et al. 2013; Ruszkiewicz et al. 2017; Garnacho Saucedo et al. 2020; Sabzevari et al. 2021). Sunscreen, often known as a sun blocker, protects against sunburn by absorbing or reflecting some of the sun's ultraviolet radiation. However, several studies reported that several sunscreen ingredients become photosensitive and unstable under exposure to ultraviolet radiation. Photosensitized sunscreen agents lose their protection efficacy, trigger phototoxic reactions and induce skin cell damage (Gonçalo 2011; Amar et al. 2015). As a result, physical and chemical measures of photoprotection are insufficient, and an alternative is necessary.

To emphasize the importance of the knowledge of ultraviolet radiation’s effect on the environment and human skin, Krutmann et al. (2017) and Passeron et al. (2020) identified several factors such as solar radiation, ultraviolet, infrared and visible light, air pollution, weather condition, personal life attributes like stress, tobacco use, slee** habits, among others that influence human health and skin conditions. The highlighted factors serve as a connecting pathway for diseases in humans, especially skin cancer, thermal discomfort, and untimely skin aging (Ivanov et al. 2018). Sunlight exposure could accelerate skin-related damage regardless of the time or season of the year, especially in the tropics (Correa et al. 2021). Skin cancer development is multifactorial (it can be caused by working with chemicals, the human papillomavirus or a weakened immune system). Still, ultraviolet radiation is the most important risk factor for skin cancer.

Recently, photoprotection findings have been solely focused on sunscreen technologies for avoiding exposure to the ultraviolet spectral range of 200–400 nm while failing to identify the ultraviolet range that offers beneficial gains to humans and the environment at large (de Assis et al. 2021). Sunscreen technologies attempt to reduce ultraviolet-induced skin cancer by absorbing, scattering or reflecting radiation (Tosato et al. 2016). Sadly, most sunscreen formulations contain organic and inorganic ultraviolet filters that are non-biodegradable in marine and terrestrial ecosystems. Epidemiological studies have reported reinvigoration of skin cells during sunbathing, vitamin D therapy, and moderate solar exposure for prolonged youthful look treatment (Arnold et al. 2018; Cohen et al. 2020).

Figure 2 shows the relation between the rates of skin cancer in the countries worldwide in 2018 (per 100,000 population) and the country irradiation per day mean (KWh/m2). The points dimension represents the average revenue per capita in the sun protection market ($). Australia has the highest irradiation per day mean and the highest rate skin of cancer. The Nordic countries (such as Norway, Denmark and Sweden) have a higher rate of skin cancer (ranging from 25 to 34 per 100,000 population), despite an average radiation level (2.3–3.4 KWh/m2) and a consistent use of sun protection products. This is probably due to skin that is more sensitive to solar radiation. On the contrary, Asian and African countries have a lower rate of skin cancer.

Fig. 2
figure 2

Country direct normal irradiation per day mean value (kWh/m2) versus rates of skin cancer in the countries worldwide in 2018 (per 100,000 population) (source: WCRF International 2018). The point dimensions represent the average revenue per capita in the sun protection market ($) for different world countries

Full size image

Sunscreen users have become increasingly interested in its composition and have found it made of synthetic materials, which pose a threat to aquatic life, eco-friendliness, eco-sustainability, and human health at large (Milito et al. 2021). Evidence is found in the ban of some ultraviolet synthetic filter sunscreens containing octyl methoxycinnamate (octinoxate) and benzophenone-3 (oxybenzone) from distribution and sale in Hawaii in January 2021 and other parts of Mexico, Palau, and the Caribbeans (Zen Life and Travel, 2022). Early pioneers in photochemistry have also verified that harm committed by visible light in other wavelengths is quite enormous, and protection against visible light must not be handled with levity (Halliday et al. 2005; Niida and Nakanishi 2006).

Although people with darker skin complexion experience less noticeable erythema symptoms manifest as redness of the skin or sunburn upon longer sunlight exposure, it is appropriate to say that carcinogenic threats and DNA damage can appear as malignant as those affecting people of lighter skin tones.

Abundant melanin pigmentation and thicker dermis layer might help to shroud wrinkles, but indirect DNA lesions and oxidative stress are catalyzed by the availability of more melanin pigments (Lee 2021). Inadequate sunlight exposure induces the prevalence of cardio-metabolic diseases, resulting in low vitamin D synthesis in Africans and Asians residing in temperate regions (Davis 2011). Therefore, to maintain a tradeoff, there is a need to enjoin people with darker skin tones to enjoy some considerable sunlight exposure and embrace other photoprotection approaches to reduce the deleterious effects of solar radiation on human health and the environment. A great emphasis is laid on exploring the photoprotective potentials of natural agents and plant materials to achieve better performance than conventional sunscreens (Anand et al. 2022b). Figure 3 shows an overview of the effect of ultraviolet radiation on the environment, human health, and ecosystem.

Fig. 3
figure 3

Multispectral effect of ultraviolet radiation on receptor organisms such as a fish and phytoplankton, and b humans in both aquatic and terrestrial habitats, respectively. Both figures show an interception of UV-C photons by cloud formation while the UV-A and UV-B spectrums penetrate beyond the photic zone in the river and ocean beds to induce DNA damage to eggs and embryos and obstruct photosynthetic pathways in phytoplankton’s metabolic activities. In humans, a dramatic increase in reactive oxygen species (ROS) during ultraviolet radiation exposure could break the DNA and cause skin erythema in mammals. Further exposure could also enhance photoaging and skin cancer while an accumulation of intense ultraviolet radiation within the 280–320 nm range could cause necrosis in humans and oxidative stress and gill damage in adult fish (Artyukhov et al. 2014; Shokrollahi Barough et al. 2015)

Full size image

Considering the increasing danger posed by the use of photoprotection that contains synthetic chemicals as sunscreens on both the ecosystem and human health, the paradigm shift toward the use of natural agents and plant materials as phytochemical alternatives to sunscreens is currently gaining momentum globally (Anand et al. 2022b). The adoption of these new materials forms the hypothesis of our research. External aggressors attacking the human body, particularly the human skin and the environment, can be mitigated significantly using efficient natural phytochemicals as active ingredients for photoprotection. To our knowledge, there are limited comprehensive review studies that specifically investigated the alternative materials as well as new approaches to overcome the negative effects of using photoprotection, including protective ultraviolet agents made from synthetic materials on human health and the ecosystem. This study aims to explore the applicability of several natural agents and plant materials as photoprotectants and their effects on human health and the environment. A systematic literature review was adopted to comprehensively assess and synthesize the available literature regarding photoprotection and associated impacts on human health and the environment. This work presents state-of-the-art knowledge on photoprotection to fill the information gap on this important topic and set the tone for future research on the use of alternative materials.

Physics of ultraviolet radiation

High-energy UV-C radiation gets absorbed by the stratospheric ozone layer. However, the characteristics of solar ultraviolet radiation depend on various factors, with the solar zenith angle being particularly significant. This angle varies with the time of day, season, stratospheric ozone concentration, pollution, cloud cover, as well as latitude and altitude. The measurement of ambient solar ultraviolet radiation has been conducted worldwide for many years. Furthermore, specialized ultraviolet radiation detectors have been developed for research purposes or individual use. For instance, a microprocessor-controlled ultraviolet radiometer has been created, equipped with short, mid- and long wave ultraviolet sensors, enabling precise measurement of solar irradiance. The intensity of ultraviolet radiation refers to the ultraviolet intensity and is measured in mW/cm2 (Goyal et al. 2015; Verma et al. 2017). The dose of light is defined as the quantity of ultraviolet or visible radiation incident on a surface, measured in Joules per centimeter square or Joules per meter square.

Advances in sensor technology for ultraviolet radiation measurement

Recent advances in the field of remote sensing and sensor development for environmental protection and health studies have extensively focused on integrating artificial intelligence with sensor technology for combating erythema, cardiovascular diseases, skin cancer, ultraviolet-induced eye defects and premature aging. Commendable recent evolution of nano- and miniaturized electronics has spurred further development of portable sensors embedded in textiles, fabrics, wearables, patches and implants to serve as either photosensitive film-based sensing devices or electronic integrated sensors (Huang and Chalmers 2021). Photosensitive film sensors are photodegradable by incident photon energy while electronic integrated sensors create an electrical current. Typical examples of these two categories are dosimeters and radiometers. Ultraviolet dosimeter or radiometer sensors are always coupled with auxiliary electronics on a printed circuit board to generate spectral responses enough to repeal ultraviolet radiation and their applicability may be enhanced by including filters to trap infrared and visible light (Grandahl et al. 2017). Skin-mounted patches and electronic sensors are quite prevalent in modern sensor markets. While the former is relatively cheaper and sunscreen-compatible, the latter is quite durable.

As a public tool for sunlight protection, ultraviolet sensors are integrated with mobile phone apps to serve as a graphical user interface for monitoring erythema dangers. It is insightful to incorporate thin ultraviolet filter films to produce several color rate changes in photosensitive film-based sensing devices. In another study, Park et al. (2019) developed a portable ultraviolet sensor with the erythemally weighted UV-B ratio using natural light. With a combination of an ultraviolet index sensor, microcontroller unit and Bluetooth module, sunburn intensity was measured, calibrated and transmitted. Validated outputs from a standard spectrometer showed promising results and indicated that the technology is adequate to quantify potential risk and damage due to ultraviolet exposure. As the field of nanotechnology expands and new knowledge is being discovered, there is a very interesting prospect for ultraviolet sensor technology.

Ultraviolet radiation in ecosystems

About 52% of the reviewed articles, as shown in the Supplementary Material, addressed the impacts of ultraviolet radiation on biotic and abiotic environments, with major reports bordering on marine/aquatic life responses to the ultraviolet effect. Generally, ultraviolet radiation in form of UV-A and UV-B penetrates beyond the stratospheric ozone layer and delivers both beneficial and adverse effects on human health, plants, air quality, biogeochemical systems, and aquatic and terrestrial ecosystems. These effects are consequential returns brought about by anthropogenic activities inducing devastating climate change effects due to ozone layer depletion. Numerous countries are embracing policies aimed at interdicting the use of chemicals and substances that deplete the ozone layer while consistently manufacturing biodegradable radiation absorbents. A typical example of such act is the Montreal Protocol signed by over ninety-seven countries of the world, with a significant reduction in trichloromethane emissions in member countries (Montzka et al. 2018).

Bernhard et al. (2020) reported that changes in ultraviolet radiation during the last twenty years have been generally minimal, resulting in less than 4% in a decade. The authors substantiated this by reporting that trend estimates of ultraviolet irradiance showed no significant difference during study periods (Chubarova et al. 2018; Zhang et al. 2019; Aun et al. 2019). Other relevant findings from Bernhard et al. (2020) revealed that atmospheric aerosol particles are projected to cause millions of premature mortalities each year globally and opined that biodegradable polymers like polylactic acid are potentially environmentally friendly options to conventional plastics for ultraviolet radiation protection. Microplastics generated by natural weathering activities driven by ultraviolet in the marine environment can be replaced by such biodegradable polymers to ensure a lesser effect of this radiation (Dhaka et al. 2022).

Chatzigianni et al. (2022) explored the effects of sunscreen products in different ecosystem biota under the deleterious effect of ultraviolet radiation. Wastewater sewers and treatment plants form the main pathway of ultraviolet filters to the environment. Domestic effluents from washing, bathing and kitchen wastes do not get properly treated and eventually get discharged into open water bodies and marine ecosystems. Indirect photolysis in an aquatic environment thereby generates toxins, like cyclodimers and benzoic acids, from the untreated effluents, with the consequence that aquatic life is greatly hampered. Direct photolysis ensures that ultraviolet filters are disintegrated into harmful products in the aquatic environment (Chatzigianni et al. 2022). Every aquatic organism responds to ultraviolet radiation differently as was reported in algae reproduction, arthropods’ synthesis of exogenous estrogen, molluscs and deformity in the tails of marine vertebrates. Also, time of sunlight exposure is a relative phenomenon across countries due to regional and meteorological variability (Correa 2015). Also, lignin—an emerging polymer used as a low-value product—can be modified by different routes to open the opportunity for its use as a high-value nanocarrier for agrochemical delivery, adsorbent for pollutants, drug delivery and natural sunscreens (Mondal et al. 2023). To provide a better understanding of the effects of ultraviolet radiation on the environment, we have summarized the findings of articles addressing ultraviolet radiation effect on the environment in Table 1.

Table 1 Effect of ultraviolet radiation exposure to aquatic environment, abiotic and biotic ecosystems. These data were extracted by the results of bibliographic analysis (see Supplementary Material)
Full size table

Photoprotection by ultraviolet filters

Encouraging photoprotection is the leading preventative health strategy involved in skin care. The natural skin protection mechanism is not effective after a short period of a few minutes, which also depends on the skin type and the intensity of ultraviolet radiation coming into that area. However, protective agents are required against solar radiation, which absorbs or reflects light and thus helps protect against sunburn. Some synthetic procedures help to protect against the ultraviolet radiation consequences (More et al. 2021). As previously stated, sunscreen lotion is used to provide photoprotection. Sunscreen contains inorganic and organic ingredients acting as filters.

Inorganic ultraviolet filters contain ingredients like titanium dioxide and zinc oxide nanoparticles, which scatter or reflect ultraviolet radiation and prevent it from reaching the skin (Saka and Chella 2021). Nevertheless, its limitation in cosmetics applications is an uneven distribution on the skin due to lum**; thus, the uncovered areas are exposed to sunlight, not resistant to water, and easily washed off by sweating and water contact giving the skin a comparatively whiter than normal shade. Moreover, organic ultraviolet filters absorbed high-intensity ultraviolet rays and are released in the form of light or heat. They are the most widely used sunscreen agents in the current scenario. It contains para-amino benzoates, cinnamates, benzophenones, salicylates and dibenzoylmethanes. Usually, these chemical filters penetrate the skin, reach the circulatory system and can have a systemic action on the body and filters undergo changes and degradation (Saka and Chella 2021).

Drugs and preservatives

The drugs, which are used for medicinal purposes, may have some side effects. Drug phototoxicity, or photosensitivity, is one such detrimental effect that has received much attention (Monisha et al. 2022). Not all but few drugs have this property of the phototoxic response. Drug-induced phototoxic refers to drug reactions triggered by ultraviolet radiation exposure to the skin. They have absorption maxima in the range of ultraviolet radiation and visible light and become photosensitive.

There are several antibiotics, anti-inflammatory, antimalarial and antifungal drugs, used to treat various diseases, but they are inducing phototoxicity. For example, ciprofloxacin and levofloxacin are broad-spectrum antibiotics. Following UV-A, UV-B and sunlight exposure, they exhibited phototoxicity and formed toxic photoproducts, potentially posing significant health risks to drug users (Dwivedi et al. 2012; Loupa 2017). Anti-inflammatory drugs such as ketoprofen, naproxen showed phototoxic products and induce dermatological complications like photoallergic responses (Liu et al. 2007; Ray et al. 2013). According to a recent study, nabumetone, which is used as anti-inflammatory medicine, loses its function when exposed to UV-A and UV-B, and rises inflammatory markers (Qureshi et al. 2021).

On the other hand, antimalarial drugs being used for the prevention and cure of malaria disease showed photosensitivity responses. The researcher reported that antimalarial drugs like quinine and mefloquine may be associated with the induction of skin diseases and cancer by altering various biological processes due to phototoxicity as well as the formation of photoproducts (Yadav et al. 2013, 2014). Furthermore, fungicidal medications are used to treat and prevent fungal infections such as dermatophytosis and candidiasis. Voriconazole and itraconazole are antifungal drugs that have been linked to liver damage, phototoxicity and cutaneous squamous cell cancer. Voriconazole therapy showed phototoxicity in children and caused immense concern (Mujtaba et al. 2018). All of these studies suggest that patients using photosensitive drugs should avoid direct or indirect sunlight exposure and be cautioned by clinicians about its potentially harmful consequences.

Moreover, the preservative is a substance or chemical, i.e., applied to things including food, beverages, pharmaceutical products, cosmetics and many other products to keep them from decomposing due to microbial development or unwanted chemical changes. However, according to recent studies, several preservatives are susceptible to ultraviolet radiation and transform their characteristics to phototoxic. The preservatives methyl paraben and triclosan are frequently utilized in pharmaceutical and cosmetic products. Photosensitized methyl paraben and triclosan showed cytotoxicity, genotoxicity, arrest the cell cycle of skin cells and triggered apoptosis as well as plate sensitivity test showed a reduction in antibacterial activity (Dubey et al. 2017).

Personal care products

Most cosmetics are chemical ingredients that are applied body’s skin surface to improve a person's appearance. Now it has been investigated that personal care products become activated followed by solar ultraviolet radiation exposures mostly UV-A and UV-B. Hair dyes are the most common personal care products in the cosmetics sector. As per the European Commission Scientific Committee on Consumer Safety, 46 hair dye ingredients act as a sensitizer (Mujtaba et al. 2018). Paraphenylenediamine and 2-Amino-3-hydroxypyridine are important ingredients used in the formulation of hair dye. According to studies, after ultraviolet radiation exposure, these ingredients become photosensitized and form toxic photoproducts, which causes genetic damage and apoptosis in skin cells (Goyal et al. 2015; Yadav and Banerjee 2018). Sunscreen is one of the personal care products that is extensively used as a safeguard for skin, but studies have reported that components of sunscreens fail to protect users (Sardoiwala et al. 2018). Sunscreen ingredients absorb sunlight to get photosensitized. For instance, benzophenone is an ingredient for sunscreen, and photosensitized benzophenone induced cell death of skin keratinocytes (Amar et al. 2015). Furthermore, lipsticks and facial creams are widely used as cosmetics. Therefore, the paper suggests that sunlight exposure should be avoided after the use of photosensitive personal care products (Yadav and Banerjee 2018).

Environmental pollutants

When coal, oil, gas, wood, waste and tobacco are burned, polycyclic aromatic hydrocarbons are generated. They are severe environmental contaminants, having the ability to bind to or create tiny particles in the air. Occupational exposure to polycyclic aromatic hydrocarbons can induce breathing problems, chest pain and vexing coughing, as well as cancer (Srivastav et al. 2018). This study reported that they can induce phototoxicity under the environmental intensity of UV-B irradiation. It also observed that UV-B activation of chrysene enhances the intercellular oxidative stress and causes apoptosis by activating caspases-3 and phosphatidylserine translocation in skin cells. Literature also reported that DNA damage as photogenotoxicity can be found under UV-B irradiation (Ali et al. 2011). Photoirradiation of polycyclic aromatic hydrocarbons has also been linked to human skin cancer due to exposure to terrestrial light (Yu 2002). For example, coal tar is used to treat psoriasis, which contains polycyclic aromatic hydrocarbons: It is applied topically to the skin followed by ultraviolet radiation exposure. This treatment has been implicated in the pathogenesis of acquiring skin cancer (Fu et al. 2020).

Fig. 5
figure 5

Plant photoprotectants. Plants, constantly irradiated by sunlight, can synthesized molecules that resist ultraviolet radiation damage, prevent photoaging and skin cancer. The most common plant secondary metabolism compounds are carotenoids, polyphenols, anthocyanidins, isoflavonoids and alkaloids. Created with BioRender.com

Full size image

Polyphenols are natural compounds widely distributed in plant foods, including fruits, vegetables, nuts, seeds and flowers. Some important dietary sources of polyphenols are epigallocatechin-3-gallate, grape seed proanthocyanidins, apples, green tea, flavonols and catechins, flavanones, anthocyanidins and isoflavones (Rasouli et al. 2017; Williamson 2017; Cory et al. 2018). These polyphenols play a potent role in antioxidant as well as anticarcinogenic and have been reported to possess substantial skin protective effects of ultraviolet radiation including the risk of skin cancers.

Epigallocatechin-3-gallate has the ability to prevent UV-B-induced leukocyte infiltration in both mouse and human skin. As a result, it may effectively inhibit the production of reactive oxygen species by these infiltrating leukocytes upon UV-B exposure (Nichols and Katiyar 2010). Furthermore, research studies have indicated that when human fibroblasts were treated with epigallocatechin-3-gallate in culture, it effectively prevented the UV-induced rise in collagen secretion and collagenase mRNA levels. Additionally, it demonstrated the ability to inhibit the binding activities of nuclear transcription factors NF-κB (nuclear factor kappa light chain enhancer of activated B cells) and activated protein (AP)-1, both induced by UV exposure. Moreover, epigallocatechin-3-gallate was found to regulate mitogen-activated protein kinase signaling pathways (Kim et al. 2001). Upon topical application to mouse skin, green tea polyphenols demonstrated a significant inhibitory effect on UV-B-induced DNA damage, as assessed through a 32P-postlabeling technique. Similarly, when human skin was topically treated with green tea polyphenols before exposure to ultraviolet radiation, a dose-dependent inhibition of cyclobutane pyrimidine dimer formation was observed (Katiyar 2016).

Grape seed proanthocyanidins belong to a class of phenolic compounds renowned for their potent antioxidant properties, safeguarding the body against premature aging, diseases and deterioration (Sharma et al. 2007). It has antimutagenic, anti-inflammatory and anticarcinogenic (Nandakumar et al. 2008) properties. In SKH-1 hairless mice, the addition of grape seed proanthocyanidins to a standard diet effectively inhibited photocarcinogenesis, as evidenced by reduced tumor incidence, decreased tumor multiplicity and smaller tumor sizes (Katiyar 2016). Grape seed proanthocyanidins also resulted in the prevention of the malignant progression of UV-B-induced papillomas to carcinomas. In the skin, grape seed proanthocyanidins were observed to inhibit the UV-B-induced infiltration of proinflammatory leukocytes. Furthermore, the levels of myeloperoxidase, cyclooxygenase-2, prostaglandin E2, cyclin D1 and proliferating cell nuclear antigen were also reduced by the presence of grape seed proanthocyanidins (Sharma and Katiyar 2010).

Teas, honey, wines, fruits, vegetables, nuts, olive oil, cocoa and grains all contain anthocyanins, which belong to the flavonoid group of phytochemicals (Nguyen et al. 2022). The anthocyanin biosynthesis in plants is regulated by light and light quality, such as UV-A, UV-B, blue and red lights (Li et al. 2020). The use of anthocyanin pigments as therapeutic agents has long been accepted orthodoxy in folk medicine around the world, and these pigments have been connected to a staggering array of health advantages (Lila 2004). A study reported that treatment of anthocyanins inhibited the production of hydrogen peroxide (H2O2) and lipid peroxide in human dermal fibroblast cells caused by UV-A irradiation. A recent study showed that anthocyanins against UV-B induced oxidative damage in keratinocyte cells and the activation of Nrf 2 (nuclear factor E2-related factor 2) signaling. Similarly, anthocyanins reduced UV-B-induced oxidative stress and cell death in BALB/c mouse skin tissues when applied topically (Li et al. 2019). These findings suggest that anthocyanin could be a promising choice for the creation of photoprotective agents.

Isoflavonoids are dietary antioxidants that may protect against oxidative stress connected to inflammation and damaging the macromolecule by free radicals and other oxygen and nitrogen oxidizers (Miadoková 2009). Genistein, the most prevalent isoflavone of the phytoestrogen chemicals generated from soy and it is a well-known potent antioxidant. In a human reconstituted skin model, the isoflavone genistein was found to be photoprotective against UV-B induced pyrimidine dimer production and proliferating cell nuclear antigen expression. It has also been suggested that genistein could be used as a potent inhibitor for photocarcinogenesis (Moore et al. 2006). Another study investigated that oral administration of soy isoflavone extract in a hairless mouse model protects UV-B-induced skin aging (Kim et al. 2004). Moreover, the pig skin model was treated with a cocktail of five isoflavone compounds, which are genistein, equol, daidzein, biochanin A and formononetin, followed by solar-simulated ultraviolet radiation exposure. They observed that this cocktail protects pig skin from photodamage as evaluated by sunburn cell development and erythema (Lin et al. 2008). All these findings support that Isoflavones provide effective photoprotection against ultraviolet radiation damage.

Carotenoids are a group of over 600 fat-soluble plant pigments that make up the carotene family. Carotenoids like lycopene, beta-carotene and lutein are abundant in fruits and vegetables (Fernández-García 2014). These carotenoids have a wide range of biological effects. They play a role in light harvesting and photoprotection as well as provitamin and antioxidant properties, in humans and animals. Carotenoids' photoprotective qualities are linked to their antioxidant activities, which effectively scavenge reactive oxygen species, such as superoxide anions, singlet molecular oxygen, hydroxyl radicals and hydrogen peroxide (Sies and Stahl 2004). Most studies have found that increasing carotene consumption reduces the severity of ultraviolet-induced erythema (Stahl and Sies 2012).

Alkaloids are nitrogenous compounds with a low molecular weight that are found in nature. Plants use it to defend themselves against herbivores and disease pathogens. It has anti-inflammatory, anticancer, local anesthetic and pain-relieving effects, as well as neuropharmacological and other activities (Anand et al. 2022a; Khare et al. 2021). Various studies have found that alkaloids such as sanguinarine, piperine and caffeine act as defenders against ultraviolet radiation damage (Dinkova-Kostova 2008; Verma et al. 2017; Gherardini et al. 2019).

Sanguinarine is generated from the root of Sanguinaria canadensis and other poppy Fumaria species. According to an in vitro study, UV-B irradiation increased the number of human keratinocyte (HaCaT) cells in the gap 2-mitosis phase of the cell cycle, but pretreatment with sanguinarine dramatically shifted cells toward the synthesis phase. On the other hand, it protected the cell from apoptosis via modulating the tumor suppressor protein p53 and pro-apoptotic BAX (BCL-2-associated X protein), BAK (BCL-2 antagonist killer 1), BID (BCL-2-interacting domain death agonist) and BCL-2 (B-cell lymphoma-2) pathways (Reagan-Shaw et al. 2006). Moreover, in vivo findings on SKH-1 hairless mice reported that pretreatment with sanguinarine significantly decreased the UV-B-mediated skin edema, skin hyperplasia and infiltration of leukocytes. Further, they also observed that sanguinarine prevented UV-B-mediated elevations in ornithine decarboxylase, proliferating cell nuclear antigen and Kiel antigen-67, all of which are indicators of cellular proliferation (Ahsan et al. 2007; Dinkova-Kostova 2008).

Piperine, which is found in black pepper (Piper nigrum), is another plant alkaloid with a long list of medical uses (Ahmad et al. 2012). It is known to improve the bioavailability of other substances and plays a crucial function in maintaining cellular homeostasis (Johnson et al. 2011). A recent study revealed that piperine was stable under UV-A/UV-B exposure viz it was not degraded under ultraviolet radiation. Piperine was also observed to lower ultraviolet radiation-mediated DNA damage, micronuclei creation and the sub-Gap 1 phase of the cell cycle, all of which helped to protect against photogenotoxicity. Further, they found that piperine protects human keratinocytes from ultraviolet radiation-induced cell damage via the NF-κB (nuclear factor kappa light chain enhancer of activated B cells), BAX/BCL-2 pathway in keratinocytes cells (Verma et al. 2017).

The outcome of several experimental studies strongly suggests that these phytochemicals could be employed in therapeutic applications like cosmetics or medicine formulations to prevent ultraviolet-induced skin damage (Nguyen et al. 2022). One of the constraints of plant photoprotectants is that biotic and abiotic factors such as crop management plans, latitude, climate and soil, affect phytochemical profiles of such plant extracts. It is quite challenging to quantify or predict the essential active ingredients in the right proportion after harvest. However, this seems to be a trivial problem as the photoprotective prospects outweigh this uncertainty. Ongoing research activities may proffer solutions to this problem in the near future. In textile manufacturing, polysorbate improved ultraviolet exposure protection and the esthetics of polyester fabric (Sk et al. 2022). Some other studies reveal that cotton-based fabrics have excellent properties for ultraviolet protection (Kocić et al. 2019). Rabiei et al. showed that ultraviolet protection of workwear fabrics can be improved by coating titania nanoparticles (Rabiei et al. 2022).

A summary of natural agents for photoprotection is presented in Table 3. The use of sunscreens, to prevent damage from sun radiation, has been largely adopted. Sunscreen formulation is characterized by synthetic materials that are a threat to aquatic life, eco-sustainability and human health. Natural agents are prepared to supplement the inadequacies of conventional sunscreens in ultraviolet radiation protection.

Table 3 Natural agents as photoprotectant alternatives to sunscreens
Full size table

Conclusion

Several concerted efforts have been made toward proffering environmentally friendly alternatives to conventional sunscreens for ultraviolet radiation protection. Also, a series of biochemical events occur when skin is exposed to UV-A and UV-B radiation from the sun. These events are the photooxidative reactions that cause skin damage. Modification of gene expression, activation or inactivation of regulatory pathways, immunological and inflammatory processes, and induction of apoptosis are all examples of photooxidative reactions that disrupt the function of cellular responses. These include, for example, sunburn, phototoxicity, photoallergy, and photoimmunosuppression. Various strategies are used to protect the skin against ultraviolet-dependent damage, but photoprotection from phytochemicals or natural agents is widely investigated. Natural agents and secondary plant extracts have been elaborately discussed and presented to offer future prospects as sustainable options for sunscreen technology. All these findings should help researchers better understand how to treat ultraviolet-induced skin damage and other skin illnesses connected to microbiome changes or ultraviolet radiation exposure. In current molecules/compounds development practice, photosafety testing remains to be an important component for natural agents. Several potential future studies would probe the question of the protective nature of phytochemicals for healthy skin. Further study about other potential photoprotectants is recommended, and a repository can be created to ensure easy retrieval of information and data for further research. Clinical trials of identified photoprotectants should be replicated to eradicate uncertainties and scaled up for mass production in cosmetic, textile and other related industries. This could pave the path for natural agents to be used in dermatologic health management while ensuring a safer environment.