(March 2010) by Dr Bruce Sutherland

There is a lot of it around now, but what is UV and how does it affect skin?

UV is light at the far end of the violet spectrum. It is invisible to our naked eyes hence “beyond” or “ultra” violet.

UV light is essential to us for the production of vitamin D in our skin. One theory as to why Europeans have developed light coloured skin is to absorb the UV light from low light parts of the world and to optimise vitamin D production. Darker skin has more melanin which absorbs and disperses UV and therefore needs more sunlight to produce vitamin D.

UV light is also the primary cause of skin cancers. New Zealand has 50,000 new cases of skin cancer per year and most GPs see new skin cancers each week in their practices. In population studies it appears that the number of skin cancers is directly proportional to the amount of UV exposure. There are several types of UV – the two important ones being UVA and UVB.

UVB comprises >90% of UV light. It is this that causes sun burn and common skin cancers by directly damaging the skin’s DNA.

UVA on the other hand does not burn skin but causes indirect damage to collagen – causing premature aging and indirect damage to DNA causing specific types of cancer like melanoma.

SPF (skin protection factor) in sun creams is measured by the amount of UVB filtering. Early sun creams thus blocked UVB but did not block harmful UVA rays. This may have been the reason for an increase in skin cancers observed with the use of early sun blocks. Nowadays most sun creams have an SPF and UVA filter.

When choosing a sun block look for a high SPF, look for a waterproof rating and look for an agent with UVA filtering or “broad spectrum” protection.