It took just one day of use for several common sunscreen ingredients to enter the bloodstream according to a pilot study conducted by the Center for Drug Evaluation and Research, CNN reported.
The levels of penetration were high enough to trigger a government safety investigation.
The study was published in the medical journal JAMA.
The four chemicals that were studied were avobenzone, oxybenzone, ecamsule and octocrylene.
The study also found that the blood concentration of three of the ingredients continued to rise as daily use continued and then remained in the body for at least 24 hours after sunscreen use ended.
24 healthy volunteers were enrolled in the new FDA study. They were randomly assigned to a spray or lotion sunscreen that contained avobenzone, oxybenzone or octocrylene as ingredients or a crème sunscreen that contained the chemical ecamsule.
The volunteers were asked to put their assigned sunscreen on 75% of their bodies four times each day for four days. Thirty blood samples were taken from each volunteer over seven days.
Of the six people using the ecamsule cream, five had levels of the chemical in their blood. These levels were considered statistically significant by the end of day one. For the other three chemicals, especially oxybenzone, all of the volunteers showed significant levels after the first day.
For the other three chemicals, especially oxybenzone, all of the volunteers showed significant levels after the first day.
Oxybenzone was absorbed into the body at about 50 to 100 times higher concentration than any of these other three chemicals they tested.
Of all of the sunscreen ingredients, oxybenzone isknown to be the most common cause of contact allergies; a 10-year study found that 70% of people had a positive patch test when exposed.
People should not stop using sunscreens, experts say.
Studies need to be performed to evaluate this finding and determine whether there are true medical implications to absorption of certain ingredients," said Yale School of Medicine dermatologist Dr. David Leffell, a spokesman for the American Academy of Dermatology.