Our findings support our hypothesis that very-light-skinned children who tan develop more nevi than those who do not tan, independent of base skin color, hair color, eye color, hours per week in the sun, skin phototype, sun protection behavior, past sunburns, and vacation sun exposure. To our knowledge, this is the first study to examine this relationship in very-light-skinned children, those at highest risk for melanoma. Compared with darker-skinned white children, those with light skin have 2 to 3 times greater risk for melanoma.51,52
The presence of high numbers of nevi has been established as an important marker for melanoma risk.7
Many or perhaps most melanomas may not arise in existing nevi,53,54
suggesting that nevus development is not required for melanoma development. Thus, numerous nevi may be a marker for UV-induced skin damage and/or genetic susceptibility to melanoma.7
Whether nevus development is directly in the pathway for melanoma or a surrogate for melanoma susceptibility, prevention of nevus development may reduce the risk for melanoma.18,21,48
Thus, tanning avoidance may reduce the risk for melanoma in the lightest-skinned, non-redhead children. In darker-skinned white children, we found that tanning had neither a risk nor a protective effect in the development of nevi.
It was somewhat unexpected to find that higher parent-reported skin phototype was protective against nevus development, while observed tanning conveyed risk for nevus development, and these effects were independent. Our measures of skin color and tanning are similar but not equivalent to parents’ ratings of skin phototype. Skin phototype includes both burning and tanning and is based on perception rather than objective measurement, and in some cases parents may have believed that their child would burn and not tan but never actually observed it because of careful sun protection practices such as use of sunscreen, clothing, and sun avoidance. Our analysis focuses on tanning while controlling for sunburn experience as reported by parents. Thus, while correlated with skin phototype, our measures of skin color and tanning provide somewhat different information, and our results regarding these measures are independent of skin phototype, as demonstrated in the multiple regression analysis. This indicates that regardless of a child’s parent-reported propensity to tan, the child’s actual tanning is a risk factor for nevus development.
We did not find evidence for an effect of number of hours spent outside in midday during the summer on nevus development, which was somewhat unexpected. Several previous studies have found an effect for daily sun exposure,16,18,55
but 1 study has not.15
The lack of relationship may be because our measure, which asked parents to estimate the amount of time the child is usually outdoors between 11 am
and 3 pm
in the summer, lacked the necessary level of sensitivity to discriminate levels of routine sun exposure. It is also possible that intermittent intense UV exposure (rather than routine daily exposure) is required for nevus development, as has been suggested by Autier and colleagues.48
Numerous studies have noted a relationship between vacation sun exposure and nevus development, including an analysis of our full cohort at age 6 years,14–16,47–49
but such a relationship was not detected in this subgroup of light-skinned 8-year-olds. Likewise, sunburns were found to be related to nevus development in previous studies, including our full cohort,12,13,15,16,18,23,48
but this relationship was not found in the present analysis. None of these previous studies focused specifically on the lightest-skinned children.
Prior studies that investigated nevus development in white children used designations such as fair skin
, light skin reflectance
, or white
to describe skin pigmentation. These studies concluded that children with fair skin, light skin reflectance, or white skin acquired more nevi than those with darker skin.21,26
Gallagher et al21
looked at white school children and found that participants who acquired deeper tans tended to have fewer nevi than those who did not tan, suggesting a protective effect of tanning. However, that study asked parents of participants to specify via questionnaire the degree of summer tan (none, light, moderate, or deep) in September. The discrepancy in results between our study and that of Gallagher et al21
may be due to several factors. First, the earlier study included all white children, while we specifically looked at the lightest-skinned white children. Second, in the earlier study, the measure of tanning was based on parents’ perceptions of depth and extent of tanning. Our measure of tanning was objective, using a Chroma Meter CR-400, during the summer months. We have found, anecdotally, that perception of tanning is not highly related to the objective measure of tanning, primarily because those with a lighter base skin color can have a greater difference between their tanned and untanned skin but appear to have a lighter tan than those who started out with a darker base color. Thus, the tanning measure used by Gallagher et al21
reflects the perceived darkness of the tan, while ours reflects a difference between tanned and untanned skin. This phenomenon is present in our own data, as parental reports of greater tanning ability were associated with fewer nevi, while objective measurements of tanning using the colorimeter showed the opposite relationship ().
Among very-light-skinned children, lack of observable tan may be due to either lack of sun exposure or lack of ability to tan. These 2 factors may further be confounded by a tendency of those who are unable to tan to spend significantly less time in the sun to avoid a sunburn. It is further possible that a subset of those who are unable to tan are also predisposed to develop fewer nevi, and thus the lower number of nevi in these individuals is due to physiologic factors rather than lack of sun exposure. For example, there may be genetic variation in the responsiveness of melanocytes to UV exposure, and in some individuals, UV exposure may stimulate both tanning and nevus development to a lesser degree than in other individuals.
The only way to definitively disentangle ability to tan from amount of UV exposure would be to randomize these lightest-skinned children to receive or not receive sun exposure and determine their skin’s response, including whether or not individual children develop a tan and how this is related to nevus development. There are obvious ethical issues with allowing exposure to UV light to perform such a study. Future studies should use larger samples to verify our findings. This issue should also be explored in populations in other geographic areas where sun exposure patterns may be different. Studies with precise measures of sun exposure, including use of sun protection such as clothing, hats, and sunscreen, could help to further clarify our findings regarding tanning and nevus development, as could use of UV dosimeters.
In conclusion, UV tanning promotes nevus development in non-redhead children with the lightest skin pigmentation. Whether nevus development is directly in the pathway for melanoma development or a surrogate marker for UV-induced skin damage and/or genetic susceptibility to melanoma, our results suggest that tanning avoidance should be considered as a measure for the reduction of melanoma risk in this population.