International Agency for Research on Cancer (IARC) classifies the role of this risk factor in cancer development.
86% of melanoma skin cancer cases in the UK are caused by overexposure to ultraviolet radiation. An estimated 50-70% of squamous cell carcinoma (SCC) and 50-90% of basal cell carcinoma (BCC) in fair skinned people are caused by radiation.
Intermittent sun exposure
Malignant melanoma risk is more closely linked with intermittent exposure to high-intensity sunlight (e.g. sunbathing or holidaying in a place with strong sunlight), than to chronic sunlight exposure (e.g. being in an outdoor occupation), a meta-analysis has shown.
Malignant melanoma risk is 60% higher in people with the highest level of intermittent sun exposure, compared with those with the lowest, a meta-analysis showed; however this effect was limited to populations outside the UK, US, Canada or Australia.
Malignant melanoma risk is around 3 times higher in people who have had sunburn once every two years, or 10 times in a decade, compared with people who have never been sunburned, a meta-analysis showed. Malignant melanoma risk is 2-3 times higher in women who had 26+ 'painful' or 'severe' sunburns in their lifetime, a pooled analysis showed. Malignant melanoma risk is increased regardless of whether sunburn occurred in childhood or adulthood.[4-6]
Basal cell carcinoma (BCC) risk is around twice as high in people who burn and never tan when exposed to the sun, compared with those who tan and never burn, a meta-analysis showed. BCC risk is 69% higher in people who tan and rarely burn, and 55% higher in people who often burn then tan, compared with those who tan and never burn.
Squamous cell carcinoma (SCC) risk is not associated with a history of sunburn, a cohort study showed.
26% of men and 33% of women in Britain actively try to get a tan, data from 1999 showed; rates were even higher in younger people. Holidays abroad by UK residents have become increasingly popular in recent decades. Climate changes may increase the strength of solar radiation and lead to more time spent in direct sunlight (due to warmer weather), with possible consequences for skin cancer incidence rates. The impact of sunscreen use on skin cancer risk remains unclear, due largely to methodological limitations and other behaviours which may accompany (and perhaps counteract) sunscreen use.[12-19]
Sunbathing, tanning or burning should not be necessary to make sufficient vitamin D to obtain health benefits.
Chronic sun exposure
Malignant melanoma risk does not appear to be associated with chronic sunlight exposure, a meta-analysis showed; however occupational sun exposure still probably increases risk over no sun exposure at all.
Adolescent and young adult melanoma risk, and possibly also childhood melanoma risk, is higher in geographical areas with higher ultraviolet (UV) levels, US data show.
BCC risk is 43% higher in people who work outdoors, compared with those who do not, a meta-analysis showed. SCC risk is 77% higher in outdoor workers compared with indoor workers, a meta-analysis showed. These associations are stronger in countries nearer the equator.[21,22]