- Steve Taylor (steve@dox.co.nz), general practitioner,
- Brian Diffey, professor of medical physics
- Sunset Road Family Doctors, Mairangi Bay, Auckland 1310, New Zealand
- Regional Medical Physics Department, Newcastle General Hospital, Newcastle NE4 6BE
EDITOR—The sun protection factor (SPF) of a sunscreen is determined after phototesting in vivo at an internationally agreed application thickness of 2 mg/cm2. Yet studies have shown that consumers apply much less than this—typically between 0.5 and 1.5 mg/cm2.1 This has an appreciable effect on protection, with typical application rates achieving a sun protection factor of perhaps one third of that stated on the product.2 This mismatch may be one contributing factor why sunscreens have been reported to be a risk factor in melanoma.3
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