Kids using a pump dispenser applied the most sunscreen in a new Australian study, but they still used less than half the amount needed for full protection.
"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.
Her results also show that kids tended to use more sunscreen when they got it from squeeze bottles than from roll-on dispensers. Diaz and her colleagues asked 87 schoolchildren 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 0.75 mg/cm2 of skin, followed by squeeze-bottle users, who applied 0.57 mg and roll-on applicator users, who got just 0.22 mg.
On average, the kids spread the sunscreen at a thickness of 0.48 mg/cm2 -- far thinner than the 2.0 mg/cm2 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 said, "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."
Thinner coating reduces effectiveness
A thinner coating 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 online in Archives of Dermatology, that Australia has the highest rates of skin cancer in the world.
Dr Ron Moy, president of the American Academy of Dermatology and a dermatologist in Beverley Hills, said that "in real-life scenarios, we know people are not putting on enough" sunscreen.
He 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.
Other forms of protection from the sun
David Buller, research director at Klein Buendel, a health education organisation, 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.
However, "Parents need to think of other forms of protection, like clothing and hats," he said.
This year, the FDA will be enforcing a new rule in the way that sunscreen can be marketed.
All products labelled 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.
"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," Diaz said.
(Reuters Health, Kerry Grens, January 2012)