Scientists at the U.S. Food and Drug Administration have shown that active chemicals in sunscreens can readily soak into the bloodstream, confirming the need for more testing on whether these products are safe, the researchers said on Tuesday.

The study, published in the Journal of the American Medical Association, replicates findings of a pilot study by FDA scientists in May. That touched off a flurry of questions over the safety of sunscreens, Dr. Adam Friedman, chairman of dermatology at George Washington University, said in a telephone interview.

"It was completely misinterpreted," said Friedman, who was not involved with the study. "Just because it's in the blood doesn't mean that is not safe. It doesn't mean it's safe either. The answer is we don't know."

The FDA has proposed a rule requiring sunscreen manufacturers to provide additional information on the active ingredients in their products.

The study authors stressed that their findings do not suggest that people should stop using sunscreen.

The latest study aimed to determine whether common sunscreen ingredients exceeded 0.5 nanograms per milliliter of blood. FDA recommends that products exceeding that threshold be tested for safety. Of the six tested, all exceeded that limit.

"Results of our study released today show there is evidence that some sunscreen active ingredients may be absorbed," Dr. Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research, said in a statement.

Woodcock said the study emphasizes the need for sunscreen makers to test whether their products are safe when absorbed into the bloodstream.

The FDA has already certified that sunscreens that block the sun's rays with minerals - such as zinc oxide and titanium dioxide - are safe, but these often leave residue on the skin.

The new study tested six chemical sunscreen ingredients from four commercially available formulations - three sprays and one lotion - on 48 people.

They tested three chemicals from the first study - avobenzone, oxybenzone and octocrylene - plus three new ones - homosalate, octisalate and octinoxate. People applied the sunscreens over 75% of their body once on the first day, then four times a day for three more days.

All six reached blood concentrations that exceeded the FDA threshold for more safety testing after just one application, and blood concentrations increased over time.

"What this tells us is how much is getting in the blood," Friedman said. "The next question is that relevant?"