We reviewed the literature on sun exposure during childhood and adolescence and risk of melanoma skin cancer during adulthood. Migrant studies generally indicate an increased melanoma risk in individuals who spent childhood in sunny geographical locations, and decreasing melanoma risk with older age at arrival to a sunny location. Individuals who resided in geographical locations close to the equator and close to the coast during childhood and/or adolescence have an increased melanoma risk compared to those who lived at higher latitudes and never lived near the coast during the same age period. Studies on intermittent sun exposure during vacation, recreation, or occupation are variable. To date, the majority of sunburn studies suggest a positive association between early age sunburn and subsequent risk of melanoma.
There was significant variation in the methodologies used for the assessment of sun exposure in the studies and there was potential for bias from misclassification in almost all of the studies. It is quite difficult to measure sun exposure accurately. Sun exposure has been quantified in a variety of ways, including: cumulative amount of exposure, type of exposure (e.g. recreational), pattern of exposure (chronic versus intermittent), and frequency of sunburn. Various approaches have been utilised to define and measure these exposures. Epidemiological studies commonly use questionnaires to obtain information on exposures of interest when studying large groups of people in free living populations. This approach has been widely adopted for the study of sun exposures and skin cancer, although inherently there is the potential for both differential and non‐differential misclassification.87,90
Differential misclassification, resulting from recall bias may have affected the results in these studies if diseased cases over‐ or under‐reported sun exposure history compared to non‐diseased controls. Furthermore, the association between sun exposure during childhood and adolescence and melanoma may be underestimated due to the random misclassification of early life exposures. This may explain the inconsistent results between studies, as well as the relatively weak observed associations.
What this study adds
- A comprehensive summary of epidemiological research on sun exposure during childhood and adolescence and future melanoma risk
- Public health recommendations for skin cancer education programmes
Several studies have reported on the reliability or reproducibility of sun exposure measures.63,87,90,91,92,93,94,95
Most studies have shown that retrospective assessment of sun exposure in adults is not indicative of the actual amounts and patterns of exposure, nor are the results reproducible.63,91,92
In a few studies, however, habitual sun exposure in adolescents was identified as a stable behaviour that is reported with an acceptable degree validity and reliability,93
while sun exposure in adults has been reported with high levels of validity95
and fair to good reliability.94
Prospective studies assessing sun exposure during different time periods of life (childhood, adolescence, young adulthood) using a reliable and quantitative method for determining ultraviolet exposure are important. Work has been done to establish standards for determining ultraviolet radiation exposure,96
which suggests the need for further research. To understand the aetiology of skin cancer, especially melanoma, and the effect of sun exposure during different time periods of life, detailed and valid exposure information must be obtained on age at first sunburn, age at last sunburn, and number of sunburns. Information should also be obtained for protective measures, such as sunscreen use and wearing of protective clothing, to allow for adjustment in the analyses.
In studies of sun exposure and melanoma, estimates of effect will be influenced by adjustment or lack of adjustment for sun sensitivity and any related “genetic susceptibility”. There is variability in individual response to ultraviolet radiation exposure which has been characterised by phenotypic measures, hair, eye, and skin colour, skin type, freckling, propensity to burn versus tan, and number of nevi. Some studies, although not all, suggest an increased risk associated with individuals who burn easily and tan poorly and are thus inherently susceptible to the effects of the sun.74
Studies assessing the effect of sun exposure on risk of melanoma may be confounded (negatively) by lack of adjustment for sun sensitivity and there may be an interaction between exposure and susceptibility. Furthermore, pigmentary traits, eye, hair, and skin colour are highly correlated with each other as well as with the ability to tan. Controlling for skin type when studying sunburn and melanoma has the potential to obscure an association because skin type is a determinant of sunburn and highly correlated with sunburn. Studies should focus on examining the interrelations between ability to tan, propensity to burn, skin type, history of sunburns, timing and pattern of sun exposure, number of nevi, and other host factors.
As skin cancer education programmes directed to children and adolescents continue to expand, an epidemiological basis for these programmes is necessary to target efforts and plan for further evaluation. There is the possibility that negative studies susceptible to publication bias may have been underrepresented in our review. Future research studies may help to clarify the relation between sun exposure during this time period of life and risk of melanoma during adulthood. Future research efforts should focus on: (1) clarifying the relation between sun exposure and melanoma; (2) conducting prospective studies; (3) assessing sun exposure during different time periods of life using a reliable and quantitative method; (4) obtaining information on protective measures; and (5) examining the interrelations between ability to tan, propensity to burn, skin type, history of sunburns, timing and pattern of sun exposure, number of nevi, and other host factors in the child and adolescent populations.