By Jim Kling

Sunscreen likely provides protection against skin cancer in some high-risk groups, but it is probably not broadly effective, according to a study of children that used the appearance of new moles as a marker of melanoma risk.

The study tied parental reports of sunscreen use and sun exposure to the number of new moles found when children were examined at the age of 15 years. There was no association between the overall number of moles and sunscreen use.

"It's not perfect, but our study is the longest-term nevus study ever conducted," said Lori Crane, PhD, professor of community and behavioral health at the Colorado School of Public Health in Aurora.

However, "I think if there was a really strong effect, we would see something different in our data," she said.

The finding calls into question the message that sunscreen protects against skin cancer, and suggests that children and parents should remain cautious about sun exposure even when sunscreen is applied.

This is a concern because more than 76,000 cases of melanoma will be diagnosed in the United States in 2016.

The study involved 499 white children who were enrolled at birth or at age 6. The researchers used colorimeter studies to stratify the children by skin tone (lighter or darker).

Each year, Dr Crane and her colleagues conducted a skin examination on the children. In addition, parents completed a survey each year that asked about the frequency of sunscreen use when a child is outside for more than 15 minutes, the thickness of sunscreen application, parts of the body protected, and other measures.

All items were weighted equally and averaged over all years to create a 10-point scale of sunscreen use.

The researchers used lagged multivariable linear regression analyses to look at the association between the number of new moles and sunscreen use, after controlling for sun exposure, sunburns, waterside vacations, skin color, hair color, eye color, freckling, and the use of other sun protection.

The only significant association they found was for lighter-skinned children who had at least three sunburns from 12 to 14 years of age. This group has significantly fewer moles if they used sunscreen than if they did not. Each 1-point increase on the scale of sunscreen use was linked to an 8% reduction in moles on the trunk and a 7% decrease in chronically exposed body sites (P = .02).

However, even that association might have occurred by chance, because the team performed many subanalyses, increasing the odds of a spurious finding, Dr Crane reported.

Sunscreen has long been touted as a protective measure against melanoma and sunburns, but some recent evidence has suggested otherwise. Sunscreens do a good job of blocking ultraviolet (UV)B rays, which are known to cause melanoma, but many do not block UVA rays. Although UVA radiation was long thought to produce only tans, it has recently been linked to melanoma.

Dr Crane said she recommends the newer broad-spectrum sunscreens that block both UVA and UVB radiation, at the highest SPF available.

UVA exposure is more or less constant throughout the day. So although the sunburn danger wanes when the sun is low in the sky, risk for UVA exposure can remain.

This is "an excellent study, very well done, and longitudinal, which is good," said Susan Nohelty, PhD, professor of public health and epidemiology at Capella University in Interlaken, New York, who presented a separate study during the session.

"I have lighter skin, so I do use sunscreen, but you have to wonder if sunscreen does help," Dr Nohelty added.

She also said she wonders if the broad-spectrum sunscreens will prove to be more beneficial. "I think it would be fascinating to evaluate the different kinds of sunscreen," she said.

In addition to recommending such broad-spectrum sunscreens, Dr Crane champions hats and protective clothing. "Kids on the beach should be wearing those swim shirts; they shouldn't be running around with just trunks or a bikini," she said. Broad-spectrum sunscreen can then be used on areas that can't be covered.