Sunscreen Chemicals in Your Blood: What the FDA Absorption Studies Do and Do Not Show

Yes. In two maximal-use pharmacokinetic trials published in JAMA, several common chemical sunscreen filters were absorbed through the skin into the bloodstream at concentrations above the U.S. Food and Drug Administration threshold of 0.5 ng/mL. That threshold is not a line between safe and dangerous; it is a regulatory trigger that tells the FDA when an ingredient needs additional safety testing before it can be called generally recognized as safe and effective. Absorption, in that sense, is a reason to study, not a verdict that anything went wrong.

What the JAMA trials measured

The first study (Matta and colleagues, JAMA, 2019) enrolled 24 healthy adults who applied one of four commercial products at 2 mg/cm2 over 75% of the body surface, four times a day for four days, with blood sampled through day seven. Four active ingredients were tracked: avobenzone, oxybenzone, octocrylene, and ecamsule. All four exceeded 0.5 ng/mL, and some did so after the first day. Oxybenzone reached the highest plasma concentrations by a wide margin.

The follow-up (Matta and colleagues, JAMA, 2020) extended the design to 48 adults and six filters, adding homosalate, octisalate, and octinoxate. The key detail here is that the geometric mean maximum plasma concentration of all six ingredients passed 0.5 ng/mL after a single application, then rose further with repeated use. Several ingredients stayed detectable in blood for days after the last application, which points to accumulation rather than immediate clearance.

Both papers carried the same caution from their authors: these findings do not indicate that individuals should refrain from using sunscreen.

Where the 0.5 ng/mL number comes from

The threshold traces to a concept called the threshold of toxicological concern. FDA guidance treats 0.5 ng/mL as the plasma level below which the theoretical additional cancer risk of an unknown compound would fall under one in 100,000 after a single dose. If a filter stays under that level and shows no other safety signals, the agency generally does not ask for a full systemic carcinogenicity study. Cross the line, and that study, along with other nonclinical testing, moves back onto the table.

Absorption is not the same as harm

This is the point most easily lost in headlines. A molecule reaching the bloodstream tells you it was absorbed. It does not tell you whether that amount produces any biological effect, harmful or otherwise. Caffeine, many foods, and nearly every oral medication reach the blood; the relevant questions are dose, duration, metabolism, and whether a toxic effect actually occurs. The JAMA trials answered the first question, absorption, and deliberately left the second, clinical consequence, open. The FDA has made the same distinction consistently: detecting an ingredient in the body is not evidence that the ingredient is unsafe.

Why "maximal use" is doing a lot of work

These were built as stress tests. Applying 2 mg/cm2 is the amount used to certify a product's SPF, and it is more than most people apply in daily life. Covering three quarters of the body and reapplying four times a day for four days indoors, with frequent blood draws, is meant to push absorption as high as it realistically goes. The resulting concentrations sit closer to a ceiling than to a typical afternoon outdoors. That design choice cuts both ways. It likely overstates everyday exposure, and at the same time it shows cleanly that absorption is real enough to justify the data the FDA is requesting.

What the FDA did with the findings

In 2020 the CARES Act changed how over-the-counter monograph drugs, sunscreens included, are regulated, replacing the older notice-and-comment rulemaking route with an administrative order process. In September 2021 the FDA issued a deemed final order setting current marketing requirements and a proposed order to update them. In that proposed order the agency proposed GRASE status for two mineral filters, zinc oxide and titanium dioxide, and proposed not-GRASE status for PABA and trolamine salicylate. For twelve chemical filters, among them oxybenzone, avobenzone, octocrylene, homosalate, octisalate, and octinoxate, the FDA said it lacked sufficient data to reach a determination and requested more, including the kind of absorption and toxicology studies these JAMA trials began to supply.

"Not GRASE" in this context means the file is incomplete, not that a filter has been judged dangerous. Those products remain legal and on shelves while manufacturers generate the requested data.

What this means if you are choosing a sunscreen

The unresolved question is narrow: what, if anything, do long-term systemic levels of certain filters do in the body. It is not a question about whether skin should be protected. Ultraviolet radiation is an established human carcinogen and a primary driver of photoaging, and the evidence for photoprotection is strong and long-standing. Someone who prefers to minimize absorption while that data gap is filled can note that the two mineral filters, zinc oxide and titanium dioxide, are the ingredients the FDA has already proposed as GRASE. This article is educational and not a substitute for individual medical advice.

The plain reading of the science is unglamorous. Chemical filters get into the blood, the amounts crossed a regulatory screening line, and that crossing obligates further testing rather than settling anything. Reading absorption as proof of harm, or the FDA's data request as a recall, mistakes the opening of a scientific process for its result.