Positive Health Online

Introduction

Solar UVR is divided into three types of radiations: UVA (320-400 nm), UVB (290-320 nm), and UVC (200-290 nm). Different wavelengths and energy associated with UV subdivision correspond to distinctly different effects on living tissue.[1] The majority is UVA (typically>95%). UVB is dampened by the ozone layer, as the ratio of UVB to UVA varies with the height of the sun, which in turn depends on latitude, season, and time of day. As a rule of thumb, a given dose of UVB causes approximately 1000 times more erythema than the same dose of UVA. Therefore, the small UVB component of sunlight is the main cause of sunburn and, therefore likely also the main cause of non-melanoma skin cancer. UVC, although it possesses the highest energy and has the greatest potential for biological damage, is effectively filtered by the ozone layer and is therefore not considered to be a factor in solar exposure of human beings and therefore not of biological relevance.[2]

A sunscreen's efficacy is measured by its sun protection factor (SPF), which is a universally accepted index of protection from erythema after a single exposure to solar simulated radiation (SSR). SPF is determined under conditions prescribed by authorities such as the European Commission (EC) or the US Food and Drug Administration. There is increasing concern about the potential adverse long-term effects of suberythemal UVA, which has led to the development of specific indices for UVA protection such as the UVA protection factor, which is a measure of protection against persistent pigment darkening, of unknown biological significance, or the ratio of UVB and UVA absorption of a sunscreen. Thus, sunscreens are labelled with SPF plus a measure of UVA protection. The SPF is only valid as a measure of protection from erythema and its relationship with other markers of acute photo damage, such as immunosuppression, is unclear.[3]

In essence, the higher the UVB content the higher the labelled SPF. Sunscreen use is widely advocated as a means of preventing skin cancer, though the empirical human evidence to support this advice is either limited or absent. This is an area of concern because of the increasing incidence of skin cancer in many white-skinned populations.[4]

Today, many cosmetic producers aim to enhance the value of cosmetic products by adding sun protection to foundations and lipsticks. This may provide some form of protection against the harmful effects of UV light and underlie local government regulations for sunscreen actives. In the USA, the Food and Drug Administration regulate the sales of colour cosmetics containing sunscreens under cosmetics and drug legislation. In Europe, sunscreen products are regulated like cosmetics. COLIPA, the trade association for the EEC, works with regulatory agencies in individual countries to establish legislation. France and Italy, unlike other EEC countries, require labelling of active ingredients and concentration present in finished products.[5]

Sunscreen Products

There is a huge array of different types of sunscreen products on market, which must provide adequate protection from harmful UV rays (UVA and UVB). There are two general types of sunscreens: chemical and physical. A chemical sunscreen absorbs the UV rays, while the physical sunscreen reflects the harmful rays away from the skin like a temporary reflecting shield.[6]

Physical Sunblocks

Zinc oxide and titanium dioxide are the two sunblocks most commonly used. Both provide broad-spectrum UVA and UVB protection. Zinc oxide in particular is a gentle, everyday use sunscreen, especially for individuals with allergies and sensitive skin and works well for children too, because zinc rarely cause skin irritation.[7]

Chemical Sunblocks

Most chemicals only block narrow regions of the UV spectrum. Therefore, most chemical sunblocks are composed of several chemicals with each one blocking a different region of UV light. Mostly, chemicals used in sunblocks are active in UVB region. Only a few chemicals block the UVA region. However sunblocks that combine both chemical and physical active ingredients exist and may contain either a physical blocking agent or avobenzone (Parsol®1789) in combination with other chemicals. However, in the USA, combinations of avobenzone and physical sunscreens are not allowed, as Avobenzone appears to be unstable when contained in formulations with physical sunscreens.[8]

Sunscreens and the Cosmetic Market

Competition amongst cosmetic manufacturers of cosmetics is intense, hence companies add value to cosmetic products by delivering sun protection in moisturisers, foundations and lipsticks.[5]

It is difficult to create smooth useful formulations which protect against harmful UVA/B rays. Broad-spectrum protection in foundations is achievable using titanium dioxide with greater scattering power and iron oxides. However, many of the organic chemicals commonly used in sunscreen products have not been established safe for long-term human use. For example, titanium dioxide based sunscreens are being promoted on the basis that they may be less harmful than organic sunscreen absorbers. But, the use of microfine titanium dioxide as a sunscreen product also has no long-term safety data. Today, manufacturers aim to use more natural components for skin protection from UV radiation. These products contain a high level of natural UV absorbers such as squalene, peptides, and nucleotides that have been protecting mammalian skin for over 100 million years.[9]

Phytomedical Cosmetics

In a quest to find new, effective and skin friendly topical photoprotective agents, plant-derived products have been researched for their antioxidant activity. Effective plant based antioxidant compounds are widely used in traditional medicine and include tocopherols, flavonoids, phenolic acids, nitrogen containing compounds (indoles, alkaloids, amines, and amino acids), and monoterpenes. As the topical application of antioxidants has been shown to affect the antioxidant network in the skin, applying plant based formulations, rich in antioxidants, reveal promising avenues for future research.[10]

Natural Sun Blockers

The skin's natural sun blockers are proteins (peptide bonds), absorbing lipids, and nucleotides. The high concentration of plant peptides protect the skins’ peptide bonds. High level of squalene (derived from olive oil) protects the skin's lipids. Squalene is the skin's most important protective lipid. Allantoin is a nucleotide that naturally occurs in the body and absorbs the spectrum of UV radiation which damages the cell's fragile DNA. Allantoin is an extract of the comfrey plant and is used for its anti-inflammatory properties. This extract can be found in anti-eczema creams, sunscreens, due to its healing and soothing properties. Some clinical studies suggest that allantoin enhance skin repair.[11]

Natural Antioxidants

The most damaging factors for the skin are oxygenated molecules, also known as ‘free radicals’. To stimulate the skin to repair and regenerate itself naturally, we need antioxidants. Plants like olive trees have their own built-in protection against the oxidative damage of the sun, and these built-in protectors function as cell protectors in our own body too. The very pigments that make blueberries blue and raspberries red protect those berries from oxidative damage.[12]

Quercetin

The most common flavonol in the diet is quercetin. Quercetin has anti-inflammatory and antioxidant effects and act as an immunomodulator. A diet rich in quercetin has been reported to inhibit a number of cancers including skin cancer. It is present in various common fruit and vegetables, beverages, and herbs. The highest concentrations are found in onion. Quercetin and rutin were tested as potential topical sunscreen factors in human skin.[13]

Silymarin

Silymarin is a flavonoid compound found in the seeds of milk thistle (Silybum marianum).  Silymarin consists of the following three phytochemicals: silybin, silidianin, and silicristin. Silybin is the most active phytochemical. Topical silymarin has been shown to have a remarkable antitumour effect. The number of tumours induced in the skin of hairless mice by UVB light was reduced by 92%. Silymarin reduced UV-induced sunburn cell formation and apoptosis. Silymarin treatment prevents UVB-induced immune suppression and oxidative stress in vivo.[14]

Curcumin

Curcumin (diferuloylmethane) is a pigment isolated from the rhizome of turmeric (Curcuma longa). Curcumin possesses anti-inflammatory, antitumoral, and antioxidant properties. It has been found that topical application of curcumin in epidermis of CD-1 mice significantly inhibited UVA-induced ornithine decarboxylase (ODC) activity. The inhibitory effects of curcumin were attributed to its ability to scavenge reactive oxygen species (ROS). Curcumin can prevent UV irradiation-induced apoptotic changes in human epidermoid carcinoma A431 cells.[15]

Vitamin E

The antioxidant vitamin E (α-tocopherol) may protect both animal and plant cell membranes from light-induced damage. Topical application of these antioxidants to the skin has been shown to reduce acute and chronic photodamage. Topically applied, only the natural forms of vitamin E - alpha-tocopherol and tocotrienol - effectively reduce skin roughness, the length of facial lines, and the depth of wrinkles.[16]

Vitamin C

Vitamin C (L-ascorbic acid) is the body's most important intracellular and extracellular aqueous-phase antioxidant. Vitamin C provides many benefits to the skin - most significantly, increased synthesis of collagen and photoprotection. Photoprotection is enhanced by the anti-inflammatory properties of vitamin C. Photoprotection over many months allows the skin to correct previous photodamage, the synthesis of collagen and inhibition of MMP-1 was proven to decrease wrinkles, and the inhibition of tyrosinase and anti-inflammatory activity result in depigmenting solar lentigines. Vitamin C is found in active form and substantial quantities in Rosehip seed extract or oil.[17]

Carotenoids

Dietary carotenoids from a healthy diet accumulate in the skin and their level significantly correlates with sun protection. Eating large quantities of fish oil can provide a sun protective effect, in some cases up to an SPF of 5, and may reduce the UV-induced inflammatory response by a lowered prostaglandin E2 levels (a mediator in the arachidonic acid cascade for inflammation). In human fibroblasts, lycopene, β-carotene, and lutein have all shown significantly reducing lipid peroxidation caused by UVB. A human trial with oral administration of lycopene β-carotene, α-tocopherol, and selenium reported decreased UV-induced erythema, lipid peroxidation, and sunburn cell formation.[17]

Whole Phytomedical Extracts In Use

Whole plant based extracts consist of numerous compounds that together provide better effects on the skin.

Camellia Sinensis

Tea (Camellia sinensis) is commonly used as a home remedy for sunburn. The tannic acid and theobromine in tea help calm down heat from sunburns. Other compounds in tea known as catechins help prevent and repair skin damage and may even help prevent chemical- and radiation- induced skin cancers.[18] The complex polyphenolic compounds in tea provide the same protective effect for the skin as for internal organs. They have been shown to modulate biochemical pathways that are important in cell proliferation, inflammatory responses, and responses of tumour promoters. Green tea has been shown to have anti-inflammatory and antioxidant effects in both human and animal skin. Animal studies provide evidence that tea polyphenols, when applied orally or topically, improve adverse skin reactions following UV exposure, including skin damage, erythema, and lipid peroxidation. Researchers have found that the main active ingredient in green tea, epigallocatechin-3-gallate (EGCG), works well as an anti-inflammatory, antioxidant, and sunscreen. Topical green tea applied to human skin provide a photoprotective effect, reduced the number of sunburns cells, protecting epidermal Langerhans cells from UV damage, and reduced the DNA damage that formed after UV radiation. Green tea was also found to decrease melanoma cell formation with topical and oral administration in mice. Although cosmetics containing tea extracts or phenols have not been tested in controlled clinical trials, they have shown compelling evidence for antioxidant, anti-inflammatory, and anticarcinogenic activities.[19]

Aloe Vera

Aloe vera or Aloe barbadensis has been scientifically proven for all forms of burn, including radiation, thermal, or solar. It has also been demonstrated that it has a prophylactic effect if used before, during, and after these skin damaging events. Clearly, the plant is mainly used for its soothing and cooling effect; however, and in order to be effective aloe has to be used at 100% to be sure of any beneficial effect. The polysaccharides, mannose-6-phosphate, and complex anthraquinones all contribute synergistically to its benefits. The natural chemical constituents of Aloe vera can be categorized in the following main areas: Amino acids, anthraquinones, enzymes, lignin, minerals, mono- and polysaccharides, salicylic acid, saponins, sterols, and vitamins. Aloe vera not only improved fibroblast cell structure, but also accelerated the collagen production process. Aloe vera is a uniquely effective moisturizer and healing agent for the skin.[20]

Juglans Regia

Walnut extract is made from the fresh green shells of English walnut, Juglans regia. The aqueous extract has been shown to be particularly effective as a self-tanning sunscreen agent. Its most important component is juglone (5-hydroxy-1, 4- naphthoquinone), a naphthol closely related to lawsone (2-hydroxy-1,4- naphthoquinone). Juglone is known to react with the keratin proteins present in the skin to form sclerojuglonic compounds. These are coloured and have UV protection properties.[21]

Krameria Tiandra

The antioxidant/photoprotective potential of a standardized Krameria triandra root extract (15% neolignans), also known as Rhatany, has been evaluated in different cell models. In cultured human keratinocytes exposed to UVB radiation, Krameria triandra root extract significantly and dose-dependently restrained the intracellular oxidative damage. The cytoprotective effect of the extract was confirmed in a more severe model of cell damage: Exposure of keratinocytes to higher UVB doses, which induce a 50% cell death. In keratinocyte cultures supplemented with 10 μg/ml, cell viability was almost completely preserved and more efficiently than with green tea. The results of this study indicate the potential use of Rhatany extracts, standardized in neolignans, as topical antioxidants/radical scavengers against skin photodamage.[22]

Plant Oils

Researchers have found that some plant oils contain natural sunscreens. For example, sesame oil resists 30% of UV rays, whereas coconut, peanut, olive, and cottonseed oils block out about 20%.[23]

Melaleuca Alternifolia

Tea tree (Melaleuca alternifolia) oil is an effective antiseptic, fungicide, and germicide. It is a popular component of many sunscreen formulations that relieve sunburn by increasing blood flow in capillaries, bringing nutrients to damaging skin.[24]

Porphyra

Porphyra (Bangiales, Rhodophyta), a red algae from eastern Asia, contains high levels of free amino acids; when exposed to intense radiations, it synthesizes UV-absorbing secondary metabolites such as mycosporine-like amino acids. There are almost seven species of Porphyra identified in India. Among all of these, nowadays Porphyra vietnamensis are gaining more attention.[2]

The Future Of Sunscreens

The growing consumer awareness of the dangers of the sun has changed the cosmetics market and therefore demand for sun care products. Phytomedical compounds are useful to treat problematic skin. Plant based sunscreens have potential to replace the modern sunscreen containing UV-filters due to associated side effects of those. Plant based sunscreens are slowly becoming more available in the form of creams, lotions and gels with labelled SPF factors.[24] However, further identification of naturally derived sunscreens from plants requires more research.

Conclusion

UV radiation is harmful to the skin. The best way to protect our skin from sun damage is avoiding direct sun exposure. Chemical components in cosmetics and sunscreens sometimes may have harmful effects on the skin. However natural ingredients are much gentler to the skin. Plant extracts have been used in medicines and cosmetics for centuries. Their potential to treat different skin conditions and improve skin appearance is well-known, however their potential as possible sunscreen agents has not been fully explored yet.

As ultraviolet (UV) radiation can cause sunburns, decreased immunity against infections, premature aging, and cancer, there is urgent need for protection from UV radiation and prevention from their side effects. Phytomedical preparations have a high potential due to their antioxidant activity, to include vitamins (A, C, E), as well as flavonoids, and phenolic acids, all well known to fight against free radical species, that are the main cause of a number of skin concerns. Although isolated plant compounds are well known to protect the skin, whole plant extracts showed greater potential due to their complex composition. Some research showed that green and black tea (polyphenols) sooth adverse skin reactions following UV exposure. Aloe vera gel can stimulate skin renewal and assist therefore in new cell growth. Spectrophotometer testing indicates that as a concentrated extract of Krameria triandra, a root obtained from a shrub growing on the mountain slopes of Peru and Bolivia, absorbs 25 to 30% of the amount of UV radiation typically absorbed by octyl methoxycinnamate. Sesame oil shields off 30% of UV rays, while coconut, peanut, olive, and cottonseed oils block ca. 20%. Juglone is known to react with the keratin proteins present in the skin to form sclerojuglonic compounds providing UV protection.

Plants do have a remarkable ability to protect themselves from UV radiation from the sun, hence are very useful to be used in sunscreen formulations for humans. Plant phenolics are one candidate for prevention of harmful effects of UV radiation on the skin and contain a number of substances which are excellent for skin health. Their potential is unfortunately not mainstream knowledge and research trials and clinical evidences are needed.

References

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