It took just one day of use for several common sunscreen ingredients to enter the bloodstream at levels high enough to trigger a government safety investigation, according to a pilot study conducted by the Center for Drug Evaluation and Research, an arm of the US Food and Drug Administration.
The study, published Monday in the medical journal JAMA, 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.
The four chemicals studied -- avobenzone, oxybenzone, ecamsule and octocrylene -- are part of a dozen that the FDA recently said needed to be researched by manufacturers before they could be considered "generally regarded as safe and effective."
In the United States, sunscreens were originally approved as an over-the-counter solution to sunburn. They came in two types: one using chemical combos to filter the sun, the other using minerals to block the sun such as titanium dioxide or zinc oxide, which leave a telltale white coating. With many people not wanting to sport a white tint, the popularity of the chemical sunscreens soared.
Because of the way they were used at the time, there wasn't a lot of concern about a potential health impact. But that soon changed, and the FDA began to ask the industry for safety testing, said David Andrews, senior scientist at the EWG.
"They were originally used in small quantities to prevent sunburn on vacation," Andrews said. "Now they recommend applying these every day, applying them to large parts of your body. And the FDA began raising concerns."
The new FDA study enrolled 24 healthy volunteers who 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 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.
"Looking through the results tables of the study, one thing about oxybenzone stood out," Andrews said. "Oxybenzone was absorbed into the body at about 50 to 100 times higher concentration than any of these other three chemicals they tested."
In 2008, the US Centers for Disease Control and Prevention analyzed urine samples collected by a government study and found oxybenzone in 97% of the samples. Since then, studies have shown a potential link between oxybenzone and lower testosterone levels in adolescent boys, hormone changes in men, and shorter pregnancies and disrupted birth weights in babies.
Of all of the sunscreen ingredients, oxybenzone is known 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.
A Swiss study found oxybenzone or one of four other sunscreen chemicals in 85% of breast milk samples, sparking concern that newborns could be exposed.
And Hawaii, the Pacific nation of Palau and Key West recently banned sunscreens containing oxybenzone and octinoxate because they cause coral bleaching and are dangerous to marine ecosystems.
So, should you stop using sunscreen? Absolutely not, experts say.
"The sun is the real enemy here," said Scott Faber, senior vice president for government affairs at the Environmental Working Group, or EWG, an advocacy group that publishes a yearly guide on sunscreens.
"It's not news that things that you put on your skin are absorbed into the body," Faber said. "This study is the FDA's way of showing sunscreen manufacturers they need to do the studies to see if chemical absorption poses health risks."
"It's important for consumers to know that for the purpose of this study, sunscreens were applied to 75% of the body, four times per day for four days -- which is twice the amount that would be applied in what the scientific community considers real-world conditions," said Alex Kowcz, chief scientist for The Personal Care Products Council.
The council was concerned, she said, that the FDA's study might confuse consumers and discourage the use of sunscreen.
When going outside, the American Academy of Dermatology recommends applying at least 1 ounce of sunscreen to all exposed skin every two hours or after swimming, including "back, neck, face, ears, tops of your feet and legs. If you have thinning hair, either apply sunscreen to your scalp or wear a wide-brimmed hat. To protect your lips, apply a lip balm with a SPF of at least 15," the academy says, adding that since UV rays are always present, sunscreen should be applied to exposed skin even on cloudy days and in the winter.
There are ways to protect yourself and your family other than sunscreen. Seek shade, especially between 10 am and 2 pm. when the sun is at its hottest, and whenever your shadow is shorter than you. Use protective clothing, such as long-sleeved shirts and pants and a hat with a wide brim, and don't forget the sunglasses.
"It's seeking shade, using clothes and when necessary using sunscreen," Andrews said, "but not using sunscreen to prolong your time in the sun."