It is likely that the incidence of melanoma can be reduced by widespread reduction in exposure to strong sunlight, particularly by children and young adults. Complete sun avoidance is clearly impractical - a simple message to patients is ‘don’t burn, don’t tan’. This can be achieved by following the SunSmart Code. When a sunscreen is used, a broad-spectrum product that protects against UVA and UVB, with an SPF rating of over 30 should be chosen.
Case-controlled studies into sunscreens have not consistently supported their beneficial effects in reducing melanoma. This is probably because many of these studies are subjected to significant confounding and bias, and were conducted before newer, more efficacious and better accepted sunscreens were introduced. The SPF rating of a sunscreen is the factor by which it protects from UVB erythema (early sunburn) and is based on controlled phototesting of untanned skin at an even application thickness of 2 mg/cm2.
For example, a product with an SPF of 15 allows an untanned individual to withstand 15 times the amount of UVB before developing erythema. In reality, most individuals do not use enough sunscreen, typically applying only 0.5 - 1.0 mg/cm2. Application thickness is often uneven, may decrease after water exposure, and re-application may be inadequate. Consequently, the effective SPF of a sunscreen may be one-third of the nominal SPF.
When sunscreens were first popularized in the early 1980s, the median SPF was 4 - 6. Some older sunscreens permitted high levels of UVA exposure to facilitate tanning and avoid burning, which might paradoxically have increased risk of skin cancer. Current sunscreens are more effective, protecting against UVA as well as UVB with typical SPF values of over 20. The impact of these newer sunscreens on melanoma prevention may take several decades to be demonstrated.
The degree to which clothing impedes penetration of UVR is known as the Ultraviolet Protection Factor (UPF) and is based on the fibre content and weave, colour, finishing process and the presence of additives. Almost 90% of summer clothing has a UPF of more than 10, and 80% has a UPF of more than 15. Clothing is therefore a reliable and effective method of photoprotection, and should be encouraged.
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1. Regulation of synthesis and secretion
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