Sunlight, sunscreens, health and melanoma (update)
Summary
Rates of skin cancer are increasing worldwide. While skin cancer is most common in Australia and New Zealand, many other traditionally less sunny countries are also now experiencing increases in this disease. In this article Dr Val Doherty provides an overview of the effects of sunlight on health, the risk factors for skin cancer and the effectiveness of sunscreens and other methods of protecting skin from exposure to sunlight.
Key Points
- Melanoma has been the most rapidly increasing Caucasian malignancy over the past 30 years; the highest incidences are in Australia and New Zealand. Melanoma incidence is expected to increase by 75% over the next decade in Scotland – the highest predicted rate for any solid cancer.
- The relation between sun exposure and melanoma is well known, but not clear-cut. The level of sun exposure in childhood and adolescence may be particularly important.
- Individuals who freckle and sunburn easily and who have light eye colours are at higher risk.
- Ultraviolet radiation (UVR) is of two types. Ultraviolet A (UVA) is more constant throughout the day and year than ultraviolet B (UVB), penetrates skin deeply and contributes to skin ageing. UVB is more intense in summer and in the noontime sun, and causes sunburn.
- Sun protection factors (SPF) quoted on sunscreens mainly apply to UVB. In the last couple of years, SPFs for UVA have become more common.
- There is evidence that sunscreens prevent squamous skin cancer, but not melanomas. There is no evidence to support the suggestion that sunscreen use increases melanoma risk.
Declaration of interests: No conflict of interests declared
Cutaneous melanoma remains one of the most fascinating and challenging conditions to treat. Worldwide incidence rates have risen more rapidly than that of any other malignancy in Caucasian populations over the past three decades.
The relationship between the sun and melanoma has long been recognised. Sunny countries, most notably Australia and New Zealand, have the highest age-adjusted incidence rates (55 and 56/100,000 respectively) in the world.1 The lifetime risk of developing melanoma in Australia is 1 in 25 for men and 1 in 34 for women. Throughout Australia there is a clear inverse relationship between incidence and latitude.
Melanoma and sun exposure
Unlike other forms of skin cancer, the relation with sun exposure is not a clear-cut one. In non-melanoma skin cancer (basal cell and squamous cell cancers), the risk is, generally, greatest in those with the highest cumulative sun exposure over a lifetime and most frequent on exposed sites, for example the head and neck. With melanoma, it seems that intermittent sun exposure, particularly that received in childhood and adolescence, is most relevant. Melanoma occurs more frequently in individuals with poor sun tolerance, that is those who freckle and burn as opposed to tan, and this is often associated with lighter eye colours. The Celtic skin type is frequently encountered in Scotland, where cutaneous melanoma has an incidence of 12.96/100,000 for women and 10.93/100,000 for men.2
The Scottish Melanoma Group has clinical, pathological and follow-up data on all cutaneous melanomas diagnosed since 1979 and remains an active multidisciplinary group involved in audit and research. This data forms one of a very small number of population-based melanoma databases in the world. Much of the work on melanoma in Scotland has been modelled on the Austr