Sunscreens are known to prevent premature aging of the skin, sunburn, and the two most common forms of cancer: basal cell carcinoma, and squamous cell carcinoma. To date however, no scientific study has shown that sun-screens can prevent the most deadly form of skin cancer, melanoma, which accounts for more than 75% of total skin cancer deaths.
The majority of studies to date on this issue have found that sun-screen use is actually associated with a higher risk of developing melanoma. One study, published in the June 1995 issue of the International Journal of Cancer found that regular sunscreen users were 50% more likely to develop melanoma than non-users even after adjusting for other variables such as age, sex, hair color and holiday time spent in sunny climates.
Another study, published in the Annals of Epidemiology in December 2007, involved researchers analyzing the results 18 studies that dealt with the issue of sunscreen use and melanoma. After pooling the results from each study, the researchers found a 20% increased risk of melanoma for sunscreen users compared to non-users. The melanoma risk associated with sunscreen use increase to 60% when only data from latitudes greater than 40 degrees from the equator was used.
The problem with sunscreens is that until recently sunscreens only offered protection against UVB radiation. While both basal cell carcinoma and squamous cell carcinoma appear to be caused primarily by UVB radiation, melanoma appears to be triggered by exposure to both UVA and UBA radiation. A study on the effects of UVA and UVB in fish found that both forms of UV radiation led to the development of melanoma.
A second problem is that while recent sunscreens offer broad spectrum protection, meaning they protect against both UVA and UVB radiation, most of these sunscreens don’t indicate the degree of UVA protection they confer. A sunscreens SPF rating is a measure of how effective it is at preventing sunburn. A sunscreen with an SPF rating of 20 for example, means a person would take 20 times longer to burn than they would if they were not wearing any sunscreen. SPF is a measure of the amount of UVB protection a sunscreen offers because it is UVB radiation that causes sunburn. The SPF rating tells us nothing about the protection it offers against UVA radiation (which doesn’t cause sunburn).
Many sunscreens claim to offer “broad-spectrum” protection, this tells the consumer nothing about how effective the sunscreens UVA protection is, only that it offers some protection. A recent study of sunscreens found that the majority of sunscreens are quite ineffective at blocking UVA radiation, even those that claim to offer broad spectrum protection. This means an individual can still be exposed to high amounts of UVA light, even when using a broad spectrum sunscreen.
Finally, humans require UVB light in order to synthesize Vitamin D. Sun screens reduce the bodies ability to synthesize Vitamin D by blocking UVB radiation. A lack of vitamin D has been associated with a greater risk of breast, colon, prostate, and ironically skin cancers.