"As (this amount) is not likely to be sufficient to prevent sunburn, it is unlikely to be sufficient to prevent skin cancer and other sun damage," said Abbey Diaz, the study's lead author and a researcher at Queensland University of Technology.

Diaz's results also show that kids tended to use more sunscreen when they got it from squeeze bottles than from roll-on dispensers.

She and her colleagues conducted an experiment with 87 schoolchildren, in which they asked the kids to put on SPF 30 sunscreen every day for three weeks.

Each week the kids had a different dispenser, either a roll-on, a pump or a squeeze bottle.

Before and after each week, the research team weighed the dispensers to determine how much sunblock had been used.

Kids using the pump dispenser applied the most sunscreen, averaging .75 milligrams per square centimeter of skin, followed by squeeze-bottle users, who applied .57 milligrams and roll-on applicator users, who got just .22 milligrams.

On average, the kids spread the sunscreen at a thickness of 0.48 milligram per square centimeter of skin -- far thinner than the two milligrams used to determine the products' Sun Protection Factor, or SPF.

"As this is only one-quarter of the amount used to test the SPF," Diaz told Reuters Health in an email, "even when using a high SPF sunscreen, children are unlikely to be well sun-protected and may, under a false sense of security, spend longer in the sun that they should."

A thinner smear could also reduce the effectiveness of sunscreen in preventing the skin damage that can lead to cancer, she said.

The authors note in their study, published in the Archives of Dermatology, that Australia has the highest rates of skin cancer in the world.

Previous research has found that routine use of sunscreen cuts the risk of melanoma, the deadliest form of skin cancer (see Reuters Health report of December 6, 2010).

"This shows how valuable sunscreen is," said Dr. Ron Moy, president of the American Academy of Dermatology and a dermatologist in Beverley Hills. But "in real life scenarios, we know people are not putting on enough."

Moy said a good rule of thumb is to use a glob of sunscreen the size of a golf ball to spread over your body.

Another recommendation that Diaz offered is to use a teaspoon for each limb, the back, and the torso and a half teaspoon for the face and neck.

David Buller, research director at Klein Buendel, a health education organization, said putting on sunscreen at thicknesses less than the recommended amount is probably still somewhat protective against sun damage if kids are outside for only a short period of time.

However, "realize that the SPF is going to be less than what's published on the bottle," said Buller, who was not involved in this study.

"Parents need to think of other forms of protection, like clothing and hats," he told Reuters Health. "There is also the need to reapply" sunscreen.

Buller said that because the children in the study used less sunscreen with the roll-on applicators, it's best to use the pumps or squeeze bottles for the initial spread.

This year, the FDA will be enforcing a new rule in the way that sunscreen can be marketed (see Reuters report of June 14, 2011).

All products labeled as "broad spectrum" must pass a test showing that they protect against UV-B light - the primary cause of sunburns - and UV-A light - the kind that contributes to skin cancer.

Moy said people should choose broad spectrum sunblock to give their skin the most protection.

Diaz said parents should also supervise their kids when they're putting it on.

"While the quality of sunscreen products has improved substantially over the last few decades, the level of protection provided is ultimately dependent on how individuals use it," she said.

SOURCE: bit.ly/yacxoq Archives of Dermatology, online January 16, 2012.

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