Sunscreen Study Showing Impact on Human Blood Puts New Pressure on Industry

"We are asking industry and other interested parties for additional safety data."


Just in time for summer, the FDA is taking a closer look at a common household goop that spends a lot of time in contact with human skin. In a pilot study released Monday in JAMA, scientists revealed data showing that four types of sunscreen chemicals can make it into the human blood stream after just one day. They point out that we have a lot to learn about the consequences of using sunscreen, one of the few creams that Americans are encouraged to lather themselves in every day.

In March, then-FDA commissioner Scott Gottlieb proposed to update the existing FDA sunscreen guidelines by calling for more information on 12 of the 16 “active” chemical components in commercial sunscreen. The FDA added that there are “insufficient safety data” to deem them totally risk free. The new pilot study, conducted by David Strauss, Ph.D., acting director of the Division of Applied Regulatory Science, is the first wave of the FDA’s re-investigation, and it’s already yielded results on four of the 12 sunscreen ingredients in question.

Strauss and his team found that after just one day, several common chemical components accumulated in the blood of 24 willing participants. He tells Inverse that this result addressed an outstanding question in sunscreen science.

“While sunscreens are already available over the counter, the science has evolved over the years and it was unknown whether most active ingredients in sunscreens are absorbed,” he says.

This paper isn't evidence that sunscreen is unsafe, but it does suggest that some formulations need to undergo additional testing. 

To be clear, the 24 participants in this trial wore a lot of sunscreen, covering 75 percent of their bodies four times a day for four days straight. That’s probably more than even the most sun-paranoid beachgoer, but Strauss adds that it represented the “maximal use condition consistent with current sunscreen labeling.” In other words, if you followed the directions on the sunscreen bottle to the letter, this is about how much you would apply.

After just one day of excessive lathering, the participants had over 0.5 nanograms of avobenzone, oxybenzone, octocrylene, and ecamsule per one milliliter of blood. These ingredients, Strauss notes, are “commonly used sunscreen active ingredients” and help deflect harmful ultraviolet rays.

What Sunscreen in the Blood Means

Strauss’s study shows that these ingredients accumulate in the blood but it doesn’t go so far as to show that these ingredients are harmful to humans (though oxybenzone, for its part, is a likely culprit behind mass coral death. The takeaway is that the sheer amount of these ingredients present in the blood is worth watching. Since all four ingredients reached a critical threshold of 0.5 nanograms per milliliter, sunscreens containing them should go through an additional round of study by the FDA intended to illuminate possible reproductive or cancer risks, says Strauss.

“FDA has provided guidance that sunscreen active ingredients with systemic absorption greater than 0.5 ng/mL or with safety concerns should undergo nonclinical toxicology assessment including systemic carcinogenicity and additional developmental and reproductive studies,” he says.

Why You Should Still Wear Sunscreen

Importantly, this study isn’t evidence that sunscreen is unsafe. It’s a “critical element of skin cancer prevention strategy,” says Strauss, who points out that the risks of not wearing sunscreen far outweigh the theoretical risks that these chemicals pose. We simply don’t know what, if anything, they do to the body.

What we do know is that these chemicals can end up in the human bloodstream in amounts that indicate that they should probably undergo further toxicity testing. Getting that process going is part of the new rule that the FDA proposed in March, Strauss adds.

“As part of this rule, we are asking industry and other interested parties for additional safety data regarding the absorption of 12 of the 16 active sunscreen ingredients currently available. Without such data, we cannot know for certain if additional testing is needed to determine the safety of repeated use.”

It’s not unprecedented for new studies on old products to resurface novel findings. Take for example, parabens or pthalates — common in many household chemicals — which were linked to early onset puberty in girls in a 2018 Human Reproduction study. It’s clear this won’t be the last of the FDA’s investigations into sunscreen, as the agency made very clear when they wrote: “In this pilot study, all four active ingredients tested were absorbed from each formulation tested, showing that absorption of sunscreens is not just a theoretical concern.”

Again, sunscreen itself isn’t the enemy, as Strauss and many others have attested. Instead, this is a call to action on behalf of sunscreen manufacturers to take a second look at their formulas right before beach season.


Importance: The US Food and Drug Administration (FDA) has provided guidance that sunscreen active ingredients with systemic absorption greater than 0.5 ng/mL or with safety concerns should undergo nonclinical toxicology assessment including systemic carcinogenicity and additional developmental and reproductive studies.

Objective: To determine whether the active ingredients (avobenzone, oxybenzone, octocrylene, and ecamsule) of 4 commercially available sunscreens are absorbed into systemic circulation.

Design, Setting, and Participants: Randomized clinical trial conducted at a phase 1 clinical pharmacology unit in the United States and enrolling 24 healthy volunteers. Enrollment started in July 2018 and ended in August 2018.

Interventions: were randomized to 1 of 4 sunscreens: spray 1 (n = 6 participants), spray 2 (n = 6), a lotion (n = 6), and a cream (n = 6). Two milligrams of sunscreen per 1 cm2 was applied to 75% of body surface area 4 times per day for 4 days, and 30 blood samples were collected over 7 days from each participant.

Main Outcomes and Measures: The primary outcome was the maximum plasma concentration of avobenzone. Secondary outcomes were the maximum plasma concentrations of oxybenzone, octocrylene, and ecamsule.

Results: Among 24 participants randomized (mean age, 35.5 [SD, 1.5] years; 12 (50%] women; 14 [58%] black or African American; 14 [58%]), 23 (96%) completed the trial. For avobenzone, geometric mean maximum plasma concentrations were 4.0 ng/mL (coefficient of variation, 6.9%) for spray 1; 3.4 ng/mL (coefficient of variation, 77.3%) for spray 2; 4.3 ng/mL (coefficient of variation, 46.1%) for lotion; and 1.8 ng/mL (coefficient of variation, 32.1%). For oxybenzone, the corresponding values were 209.6 ng/mL (66.8%) for spray 1, 194.9 ng/mL (52.4%) for spray 2, and 169.3 ng/mL (44.5%) for lotion; for octocrylene, 2.9 ng/mL (102%) for spray 1, 7.8 ng/mL (113.3%) for spray 2, 5.7 ng/mL (66.3%) for lotion, and 5.7 ng/mL (47.1%) for cream; and for ecamsule, 1.5 ng/mL (166.1%) for cream. Systemic concentrations greater than 0.5 ng/mL were reached for all 4 products after 4 applications on day 1. The most common adverse event was rash, which developed in 1 participant with each sunscreen.

Conclusions and Relevance: In this preliminary study involving healthy volunteers, application of 4 commercially available sunscreens under maximal use conditions resulted in plasma concentrations that exceeded the threshold established by the FDA for potentially waiving some nonclinical toxicology studies for sunscreens. The systemic absorption of sunscreen ingredients supports the need for further studies to determine the clinical significance of these findings. These results do not indicate that individuals should refrain from the use of sunscreen.