Edit How effective are sunscreens

<p><em><strong>Could you explain for me - how UVA damages the skin in terms of ageing, and - is it UVA that can lead to cancerous cells?</strong></em></p> <p>UVA, UVB and UVC can all damage collagen fibres and thereby accelerate the ageing of the skin. Both UVA and UVB destroy vitamin A in the skin causing further damage. In the past, UVA was considered less harmful, but today it is known that it can contribute to skin cancer via indirect DNA damage (free radicals and reactive oxygen species). It penetrates deeply but it does not cause sunburn. UVA does not damage DNA directly like UVB and UVC, but it can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA. Because it does not cause reddening of the skin (erythema) it cannot be measured in SPF testing. Some doctors blame the absence of UVA filters in sunscreens for the higher melanoma risk that was found for sunscreen users.</p> <p>UVB light can cause direct DNA damage. The radiation excites DNA molecules in skin cells, causing abnormal bonds to form, producing something called a dimer. When DNA enzymes come along to replicate this strand of DNA, it reads the dimer wrongly causing a mutation, which can result in cancerous growths. This cancer connection is one reason for concern about ozone depletion and the ozone hole. UVB causes some damage to collagen but at a very much slower rate than UVA.</p> <p><em><strong>Also, do you know if sunbeds are just solo UVA rays, is that why people can use them UVB is absent?</strong></em></p> <p>A sunbed emits typically 95% UVA and 5% UVB, +/-3% to produce a cosmetic tan.</p> <p><em><strong>I'd say 50-100 on each would be perfect. I'm not trying to do a really high-tech piece but I thought if people knew that SPF50+=PPD22, it might make people top up more often rather than thinking that would be enough coverage for a whole day you know?</strong></em></p> <p> </p>

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