A study funded by the National Cancer Institute suggests that taking the kids on shore vacations is associated with increased numbers of nevi, which may increase their risk of developing skin cancer some day, researchers here said. Although moles are not dangerous in themselves, they do serve as markers for past sun exposure. The study also suggested that each trip to a shore before the age of seven was associated with a 5% increase in small nevi(mole) (95% CI 1% to 9%) after controlling for sunburns, said Lori Crane, Ph.D., of the University of Colorado, and colleagues from the examinations of 682 white children and interviews with their parents. The nevi markers of past sun exposure are an indirect measure of future skin cancer risk.

In the February issue of Cancer Epidemiology, Biomarkers and Prevention, Dr. Crane and colleagues wrote that "Parents should be aware of the effect that vacations may have on their children's risk for developing melanoma as adults and they should be cautious about selection of vacation locations." They also pointed out that parental education and income were associated with more frequent waterside vacations, suggesting that higher socioeconomic status may increase children's future skin cancer risk. The study did not address development of skin cancers and was conducted in children born in 1998 and who lived continuously in Colorado, where there are approximately 300 sunny days per year, so the children's sun exposure was relatively high to begin with.

Children in the study underwent exams at age seven, during 2005, yielding counts of nevi less than 2 mm in diameter and larger nevi.

Parents were interviewed each year from 2003 to 2005 to gather data on vacations, sun exposure, and sun protection.

Vacations were classified either as waterside or not, depending on whether it was likely that children would be outside in swimwear for long periods.

Thus, any trip to a location featuring a body of water known for recreational activities ordinarily associated with such activities as surfing, water skiing, and boating, but excluding fishing, was counted as waterside.

The researchers also took the time of year for vacations and the destination's general climate into account in determining whether a trip involved significant sun exposure.

On that basis, trips to Hawaii were considered waterside at any time of year; vacations to coastal North Carolina were waterside only in the summer; and visits to San Francisco were never waterside because vacationers there rarely engage in swim-related activities.

The association between a history of waterside vacations and having nevi at age seven was significant only for smaller nevi, and only when vacations during the year prior to examination were excluded.

Factors such as use of hats and sunscreens, eye color, and tanning sensitivity were not predictive of nevi.

The data also indicated that the length of vacations and the total estimated ultraviolet exposure was not a factor in nevus counts -- only the number of vacations appeared to have an effect.

Dr. Crane and colleagues said there may be a threshold effect at work, such that the radiation necessary to induce nevi is received early in a vacation and additional exposure does not increase nevus formation further.

Male gender was also a risk factor for nevi, with a 19% increase in small nevi (95% CI 6% to 33%) relative to girls.

Hispanic ethnicity appeared to be protective, reducing the likelihood of nevi by 35% compared with non-Hispanic whites (95% CI 21% to 47%).

Not surprisingly, a history of sunburn as reported by parents was associated with larger numbers of nevi, as was the presence of facial freckles.

Dr. Crane and colleagues thought it was important that vacations during the year prior to examination did not appear to contribute to nevus formation in the study.

"It suggests a time lag of at least one year for the effects of sun exposure during waterside vacations to result in new nevi," they hypothesized.

Alternatively, they said, perhaps age six to seven is a pivotal period in children's dermal reactions to sun exposure.

"It is plausible that children's melanocytes become less susceptible to the intense sun exposure received on waterside vacations as they age and that after age six the effect of waterside vacations on nevus development becomes undetectable," the researchers said.

Limitations to the study included reliance on parental interviews for data on vacation and sunburn history and other important variables. The study did not collect specific behavioral information related to waterside vacations and only recorded detailed information on the first seven vacations reported.

Also, it did not address children's later development of skin neoplasms.