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Some background - Some recent research has strongly suggestedthat UVA penetration into the skin is far more dangerous than UVB,a very good example is this paper by Agar et al. (2004).

My query is, is there a measure that relates the UV wavelengthwith the penetration depth into human skin? Related, is the answerto this related to skin types?

Posted Aug 26 2019

Answered on Aug 26 2019
Solar UV radiation is widely classified as UV-A,B and C(decreasing order of wavelengths). The penetrating ability of UV is not a direct function of its wavelength; the less the wavelengthless is the penetrating ability (but the higher is the energy: the direct function of the wavelength). The ability to penetrate depends on dispersion and absorption. Most biomolecules in the skin, including melanin and proteins, absorb around 220-300nm. Moreover, scattering (esp Rayleigh scattering) is inversely proportional towavelength. Since UV B has higher energy than UV A, the former is more toxic to cells. But a little UV B also does some good; conversion of 7-dehydrocholesterol to vitamin D. UV A does not have enough energy to cause DNA damage directly, but it can give riseto free radicals and cause DNA damage indirectly. The paper you mentioned says that the tissue they studied has more UV A lesions. This could be due to the increased availability of UV A to the cells. Ozone filters a majorchunk of UV B and C and melanin does little more. If the mechanisms did not exist, high-energy UVs would have burnt. To summarize, the inherent order of toxicity is C > B >A

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