• #5-2. Sunscreen overview


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    Formulation types of sunscreens


    Sunscreens are available in the various types of cream, lotion, gel, stick, etc to suit the needs of the user. How much should be applied for adequate protection? The amount used to measure SPF is not practical to apply on skin. Therefore, it is recommended to use a sunscreen with SPF of at least 30. Depending on the amount applied and SPF level, the UV screening effect varies in an S shaped curve. SPF is a measure of a sunscreen’s ability to block UVB. It is defined as the UV energy required to produce a minimal erythema dose (MED) on protected skin. PPA which is a measure of a sunscreen’s ability to block UVA is expressed in the ‘+’ and not in numbers. Higher number of ‘+’ indicates higher protection against UVA.



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    Although, topical sunscreens have much better efficacy, oral UV screening agents have also been tried. Antioxidants that reduces harmful effect of UV radiaitons in food include carotenoids, tocopherols (vitamin E), ascorbic acid (vitamin C), flavonoids/polyphenols, and monounsaturated fatty acids, etc.


    Carotenoids is rich in carrots, sweet potatoes, kale, spinach, tomatoes, and mangoes. Carotenoids such as beta-carotene, alpha-carotene, lutein, lycopene, and zeaxanthin, etc are found in the human body. Carotenoids are converted from cis-carotenoid to trans-carotenoid to turn light energy into heat and remove singlet oxygen. The absorption peak is 400∼450nm and the maximum daily dose in treatment of erythropoietic protoporphyria is 180∼300mg.

    Lycopene, abundant in tomatoes, inhibits mitochondrial damage from UV radiations and inhibits MMP-1. It also inhibits fibrillin-1 reduction and increases procollagen I. Carotenoids should be taken for at least 10 weeks, with the minimum daily dose of 20mg to bring protection against UV radiations.

    Vitamin C is hydrophillic antioxidant necessary in collagenesis. It is involved in the formation of stratum corneum lipids and strengthens the skin barrier. Vitamin E is an antioxidant of the cell membrane and works with vitamin C to give photoprotection. Vitamin E and vitamin C work together to reduce oxygen free radicals that attack cell membrane. Vitamin E oxidation leads to oxidation of vitamin C that reduces vitamin E. Vitamin C is reduced during glutathion oxidation and glutathion is reduced when NADH is oxidized into NAD.


    Coenzyme Q (ubiquinol) is a cell membrane antioxidant which reduces vitamin E and is oxidized into ubiquinone. Vitamin E is fat-soluble and 50-70% of ingested amount is absorbed. Daily intake of 800mg of Vitamin E for years has been shown to cause no side effect. Alpha-tocopherol is the most common and bioavailable form. vitamin E rapidly removes lipid-peroxyl radical to prevent interaction of cell membrane with other lipids.

    Coenzyme Q is an electron & proton carrier of all cell membranes and Low Density Lipoprotein (LDL) and is fat-soluble. The most common form in humans is coenzyme Q10. It has similar actions as vitamin E and the reduced form of ubiquinol reduces peroxyl radical to inhibit peroxidation of the lipid membrane. It reduces vitamin E inherent in the lipid membrane. Vitamin C can only be obtained from food. It is found in all layers of the skin and administration of vitamin C alone cannot reduce erythema but combination with vitamin E increases MED to UVA and UVB.

    Nicotinamide is an amide form of vitamin B3. It has no toxicity at a high daily dose of 5.5 g. It is rich in meat, vegetables, nuts, grains, coffee and tea. It is also synthesized in the liver using tryptophan contained in eggs, dairy products, fish, meat and beans. It has photoprotective effect but is exhausted on the epidermis by UV irradiation. It restores the skin barrier function by increasing production of epidermal lipids such as ceramide as well as proteins such as keratin, involucrin, and filaggrin.

    Plant-derived flavonoids has low toxicity and high absorption with antioxidative activity. Flavonoids are rich in varous vegetables and fruits including green tea (epigallocatechin-3-gallate: EGCG), tea, red grape peels (resveratrol), cacao/grape seeds (proan-thocyanidin), berries (anthocyanidins), beans (genistein, isoflavone), onion (flavonol), citrus fruits (flavonone), etc. Polyphenol is mostly pigmented and topical application has UV protective effect. It also has the systemic effect of anti-inflammatory action, immunomodulation, antioxidation, DNA repair and inhibits photocarcinogenesis. Polyphenol found in green tea is a more powerful antioxidant than vitamin C and vitamin E and has anticancer, anti-inflammatory, and matrix metalloproteinase (MMP) inhibition activity. Resveratrol rich in grape peel, nuts, fruits and red wine inhibits production of hydrogen peroxide and NO and prevents oxidation of lipids and proteins. It also inhibits activation of MAPK and NF-κB and prevents apoptosis by activating p53.

    Grape seeds are rich in proanthocyanidin. It is a stronger antioxidant than vitamins C and E and prevents exhaustion of antioxidative protectants from UVB. Isoflavone is phytoestrogen with similar actions as estrogen and can remove radical to prevent hyperoxidation of lipid and oxidative damage of DNA. It is abundant in peas. Isoflavone most abundant in beans is a genistein with powerful antioxidant, anticancer, anti-inflammatory, anti-aging effect and very low toxicity.

    Omega-3 and omega-6 polyunsaturated fatty acid (PUFA) can only be obtained from food ingestion. Long-chain omega-3 PUFA is found in oily fish and seeds. Sufficient intake of Omega-3 PUFA competes against inflammatory omega-6 PUFA to act on cyclooxygenase (COX) and lipoxygenase (LOX). This creates eicosanloids weaker than eicosanoids produced by arachidonic acid to alleviate inflammation.


    Importance of a hat, parasol, and sun glasses


    Another important method of UV protection involves clothing, parasol, hats and sun glasses. Cool, light and soft materials have been developed to allow more coverage of the skin while still staying cool in summer. Wide rimmed hats are not only for fashion but are an excellent way to protect the face against harmful sun rays.

    Today’s dermatologist should be well updated in the variou types of topical, oral and wearable sun screens as well as their efficacy to educate patients to better protect their skin from harmful rays of the sun.


    -To be continued-


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