Sun damage or photo damage produces both skin cancers as well as photo-aging. Photo-aging shows itself on the skin as wrinkling, scaling, dryness, and mottled pigmentation. Ultra-violet light is absorbed by skin, which in turn produces a photo-chemical reaction.
The UVA light is absorbed by both DNA as well as urocanic acid, the photo-chemical reaction produces oxidation of both DNA, nucleide acid, and protein, as well as lipids, this is known as oxidative damage. Anti-oxidants have been evolved to protect against, and reverse some of the damage produced by sunlight. An anti-oxidant mechanism is very advanced in plants that protect against the damage from sun exposure.
Oxidation is produced by reactive oxygen molecules. The DNA absorbs ultra-violet light mostly in the UVB (290-320 manometres) range. This produces damage mainly within the epidermis. UVA (320-400 manometres) penetrates deeper into the skin and produces damage in the epidermis, the dermis as well as affecting blood vessels. The UVA has a much more oxidizing effect on cells.
The carcinogenic or cancer forming effects of ultra-violet B produce mutations within the DNA. This initiates tumours within the epidermis. The UVA promotes these tumours as it has much more oxidizing stress on the skin than UVB. It may as a result be more cytotoxic and immunosuppressive.
Sunscreens certainly protect against ultra-violet light, the sunburning spectrum is UVB and sunscreens are very effective. Ultra-violet A is the most difficult to protect against. It is important to realize that the SPF numbers are calculated with an amount of sunscreen on skin that exceeds what most of us put on our own skin.
The SPF is calculated with a quantity of 2mg. of sunscreen per centimetre2. Most people will put on about half to one quarter of this when used as sun protection. Unfortunately, low quantities of sunscreen of per centimtre2 will have minimal sun protective effects. Usually if 5mg. per cm.2 of sunscreen is applied to the skin, the sun protective factor is in the region of an SPF of 3.
Anti-oxidants play a significant part in the protective and repair mechanisms within animals and plants. This can be achieved by anti-oxidants that are produced within the skin itself or by those consumed or applied from plants. The anti-oxidant effects can be divided into those that have their protection through enzymes, and those that tend to reduce the quantity of hydrogen peroxide as well as lipid hydroperoxides.
Topical Anti-Oxidants]
The use of topical anti-oxidants has certain requirements, these have to be stable as well as being cosmetically acceptable. It is clear that anti-oxidants have a photo-protective benefit. The physiological anti-oxidants include vitamin C, vitamin E, and ubiquinol. Vitamin C is water-soluble and is a free radical scavenger, it is required for collagen synthesis and may inhibit elastin formation in the dermis.
It may also reduce pigment synthesis, as well as enhance epidermal barrier function. For it to be active it must be present on the skin at a pH of 3.5 or lower in order to have an anti-oxidative effect. Vitamin E is different from vitamin C, in that it is lipid soluble, there is evidence that combining vitamin E and vitamin C may be of some benefit. Other anti-oxidants to be considered will be selenium as well as zinc.
[b]Plant Anti-Oxidants]
Plants synthesize vitamin C, vitamin E and flavones, and polyphenolic compounds.
This is a Milk Thistle extract, the main component in terms of anti-oxidants is silybyn. This prevents lipid peroxidase action. It also has been shown to inhibit tumour promotion in animals.
[b]Soy isoflavones]
Soy has been connected with a reduction in cardiovascular disease, and in some incidents' of breast cancer when taken by mouth in large quantities. It has a phytoestrogen effect, which can reduce menopausal symptoms. The isoflavones are genistein and gaidzein. The genistein has a collagen synthesis effect. It is also anti-cancer. It has been used both orally as well as topically.
The genistein is a powerful scavenger of peroxyl radicals. This has a significant reduction in lipid peroxidase activity. It has been shown to reduce redness in the skin of mice which are subject to ultra-violet A. It also has an anti-inflammatory effect. The use of this compound reduces the immune suppression effect of ultra-violet light.
[b]Tea polyphenols]
Tea is fermented initially to green, and then to black tea. The drinking of black tea has been shown to reduce the frequency of squamous cell carcinomas. Work done with green tea both topically and taken orally, shows that it reduces the ability of ultra-violet to produce skin cancers and redness, particularly in animals. The possibility of combining tea, plus vitamin E, to work together as anti-oxidants is interesting.
Much more work needs to be done in order to establish how combining anti-oxidants with sunscreens will have a very beneficial effect on reducing sun damage to skin.
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