Chemistry of Sunscreen

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The chemistry of sunscreen is highly relevant to deep level skin damage caused by UV radiation. Human skin has an incredible capability to rapidly repair and heal most types of surface damage, such as grazes and mild burns. However, any injury occurring to your skin cells at a deeper level, including the damage done through too much exposure to the sun's UV rays - can have a permanent detrimental effect on your skin tissue.

Unless sunlight is deflected by the upper layers of the epidermis, the ultraviolet radiation strikes at the nucleus of your basal cells, altering the DNA within them. Instead of renewing themselves perfectly, they will tend to divide defectively. As the effect is cumulative, a small amount of sun exposure is okay, but repeated and intensive sunbathing over the years is not.

UV rays carry high energy and are suspected of causing cancer through damage to the skin's DNA. High energy in sunlight comes in two forms:

  • UV-A (320-400 nanometers) and
  • UV-B (290-320 nanometers)
  • The UVB waves tend to receive more criticism than the less energetic UVA waves.

    But, in actual fact, both UVB and UVA can damage the skin. Unfortunately, the chemistry of sunscreen, in most cases, does not enable the blocking of UVA as effectively, if at all, as they do UVB.

    So, in designing a successful formula the chemistry of sunscreen focuses on two key things:

  • preventing harmful UV-A and UV-B rays from damaging the skin
  • while allowing the skin to develop a tan
  • Chemical sunscreens protect the skin by absorbing the light particles (photons). When this energy is absorbed, the molecules of the sunscreen are destroyed, rather than a skin component. This still results in chemical reactions and the process generates free radicals that produce the same type of secondary free radical damage that unprotected sun exposure produces.

    Subsequently, chemical sunscreens are not the most complete or effective form of sun protection. They prevent a larger degree of the initial sun damage but allow secondary free radical damage, which adds to the speed of the skin aging process. The chemistry of sunscreen thus becomes an integral part of an anti-aging strategy.

    Physical sunscreens, such as titanium dioxide and zinc oxide, work by reflecting the photons of light up and out of the skin so there is no absorption of energy. Hence also, there is no chemical reaction. Unlike chemical screens, the physical screen produces no free radicals and no secondary skin damage. This is predominantly why dermatologists will recommend that the chemistry of sunscreen should include either the titanium dioxide or zinc oxide physical screens, or a combination of both as a superior sun protection.

    Physical sunscreens therefore provide much better anti-aging benefits than chemical sunscreens because physical screens eliminate much of the secondary free radical damage that can result from sun exposure.

    "Ultraviolet radiation is known to cause several forms of skin cancer, including basal cell carcinoma, squamous cell cancer and deadly melanoma"
    ...said Kerry Hanson, a postdoctoral research scientist in the University of Illinois's Laboratory for Fluorescence Dynamics. She developed a technique to peer into the skin and study how it is affected by ultraviolet radiation, and said that the addition of antioxidants in the skin can help prevent skin cancer and keep skin firm and young looking.
    "But many important questions remain, such as in which layers of the skin, and in which parts of skin cells, the initial damage occurs."

    To study the effects of ultraviolet radiation on free radical generation and the role this plays in skin damage, Hanson employed a two-photon laser fluorescence-imaging microscope. She imaged the skin at varying depths after ultraviolet exposure, looking for fluorescent tags that would reveal the presence of free radicals. She also looked for resulting damage in the skin cells.

    Using the technique, Hanson found that the stratum corneum - the skin's main protective barrier against environmental assault - generated a tremendous number of free radicals when exposed to ultraviolet light.

    "These free radicals caused considerable damage to both the cytoplasm and the lipid matrix"
    ...she said.
    "The cytoplasm of the lower epidermis was also dramatically damaged."

    She also stated that, while...

    "typical sunscreens offer no protection against free radical damage, the addition of antioxidants could significantly reduce the generation of free radicals".

    Today, the chemistry of sunscreen is strongly influenced by the addition of antioxidants into formulas as they reduce additional potential free radical damage. Physical sunscreens fortified with antioxidants are a highly effective anti-aging strategy and tool.

    Sunscreen lotions vary enormously in ingredients. The following chemical compounds found in sunscreen formulas are approved by FDA legislation.

    FDA allowable active ingredients:

  • p-Aminobenzoic acid (PABA) - up to 15 %
  • Avobenzone - up to 3%
  • Cinoxate - up to 3%
  • Dioxybenzone - up to 3%
  • Homosalate - up to 15%
  • Methyl anthranilate - up to 5%
  • Octocrylene - up to 10%
  • Octyl methoxycinnamate (Octinoxate) - up to 7.5%
  • Octyl salicylate (Octisalate) - up to 5%
  • Oxybenzone - up to 6%
  • Padimate O - up to 8%
  • Phenylbenzimidazole sulfonic acid (Ensulizole) - up to 4%
  • Sulisobenzone - up to 10%
  • Titanium dioxide - up to 25%
  • Trolamine salicylate - up to 12 %
  • Zinc oxide - up to 25%
  • Mexoryl SX (Ecamsule) - UVA absorber
  • The following list, in addition to the above, is approved by the EU and other parts of world in chemistry of sunscreen:

  • 4-Methylbenzylidene camphor (Enzacamene)
  • Tinosorb M (Bisoctrizole)
  • Tinosorb S (Bemotrizinol)
  • Mexoryl XL (Drometrizole Trisiloxane)
  • Neo Heliopan AP (Bisdisulizole Disodium)
  • Uvinul A Plus (Diethylamino Hydroxybenzoyl Hexyl Benzoate)
  • Uvinul T 150 (Octyl Triazone)
  • Uvasorb HEB (Iscotrizinol)
  • Parsol SLX (Polysilicone-15)
  • Amiloxate (Isoamyl p-Methoxycinnamate)
  • References:
    Hanson Kerry M.; Gratton Enrico; Bardeen Christopher J. (2006). "Sunscreen enhancement of UV-induced reactive oxygen species in the skin". Free Radical Biology and Medicine 41 (8): 1205-1212



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