Six sunscreen filters reach the bloodstream. Nobody has shown that it harms anyone

Chemical sunscreen filters are absorbed through the skin into the blood, at concentrations well above the level at which the US Food and Drug Administration asks for further safety testing. That is an established finding, produced by the FDA itself. What it means for health is not known, and the researchers who produced it said so in the paper.

What the trials did

In a randomised trial conducted at a clinical pharmacology unit in West Bend, Wisconsin, in January and February 2019, 48 healthy participants were assigned to one of four sunscreen products — a lotion, an aerosol spray, a non-aerosol spray and a pump spray, twelve participants each [s1]. Each product was applied at 2 mg/cm² to 75% of body surface area, once on day 1 and four times a day at two-hour intervals on days 2 through 4. Thirty-four blood samples were collected from each participant over 21 days [s1]. Participants had a mean age of 38.7 years, half were women, and the sample was split almost evenly between white and African American participants [s1]. Forty-four of the 48 completed the trial [s1].

All six active ingredients tested — avobenzone, oxybenzone, octocrylene, homosalate, octisalate and octinoxate — reached geometric mean maximum plasma concentrations above 0.5 ng/mL, and every one of them crossed that threshold on day 1, after a single application [s1].

The concentrations were not uniform. For oxybenzone the overall maximum plasma concentrations were 258.1 ng/mL for the lotion and 180.1 ng/mL for the aerosol spray — two orders of magnitude above the rest of the field [s1]. Homosalate reached 23.1 ng/mL in the aerosol spray, 17.9 in the non-aerosol spray and 13.9 in the pump spray [s1]. Avobenzone peaked at 7.1 ng/mL in the lotion and between 3.3 and 3.5 ng/mL in the three sprays; octocrylene at 7.8 in the lotion; octinoxate at 7.9 in the non-aerosol spray; octisalate at 5.8 [s1]. The most common adverse event was rash, in 14 participants [s1].

This was the larger of two trials. A pilot the previous year, enrolling 24 healthy volunteers, had tested avobenzone, oxybenzone, octocrylene and ecamsule and found the same pattern [s2].

What the 0.5 ng/mL threshold is, and is not

The number is regulatory, not toxicological. FDA guidance states that sunscreen active ingredients with systemic absorption greater than 0.5 ng/mL, or with existing safety concerns, should undergo non-clinical toxicology assessment — including systemic carcinogenicity studies and additional developmental and reproductive studies [s2]. Crossing it does not mean a substance is harmful. It means the agency will not waive the studies that would establish whether it is.

The trial authors were unusually explicit on this point, writing in the paper's own conclusions that the findings "do not indicate that individuals should refrain from the use of sunscreen" [s1]. The CMAJ review of sunscreen safety adds the missing arithmetic: these were maximal-use conditions, and most people apply far less than the tested quantity [s3]. Its assessment is that the clinical importance of absorption is not yet known and that further research is needed to determine whether there are health consequences at all [s3].

One detail from the pilot deserves more attention than it usually gets: the investigators observed long half-lives for each ingredient, which raises the possibility that regular use leads to accumulation in the body rather than clearance between applications [s3].

The endocrine question

The concern that follows absorption is whether these compounds do anything hormonally. Here the evidence is thin in a specific way — it exists, and it is not good enough to conclude from.

A meta-analysis found oxybenzone associated with reproductive adverse effects in fish, but the CMAJ review characterises the summarised literature as non-uniform and the results as uninformative [s3]. Among humans, a prospective study reported reduced fecundity in men exposed to benzophenone-2 and 4-hydroxybenzophenone, a finding the review says could be explained by confounding [s3]. A systematic review covering animal and human studies reported that high oxybenzone exposure during pregnancy was associated with decreased gestational age in male neonates and decreased birthweight in female neonates — with high heterogeneity limiting how far the finding can be taken [s3].

None of these are null results, and none of them are demonstrations. They are the reason the toxicology studies were requested.

Mineral filters are a different case

Titanium dioxide and zinc oxide are not systemically absorbed in the way the organic filters are. An in-vitro study found that fewer than 0.03% of zinc nanoparticles penetrated the uppermost layer of the stratum corneum, with none detected in the lower stratum corneum [s3]. The historical objection to mineral sunscreens was cosmetic — the white cast that encourages people to apply too little — and formulation advances have reduced it [s3].

Where the regulator stands

The FDA's current consumer guidance states that there is evidence at least some sunscreen active ingredients are absorbed through the skin and enter the body, that this makes it important for the agency to determine whether such exposure carries safety risks, and that it has requested data from industry to confirm the safety of sunscreen active ingredients [s4]. In the United States sunscreens are regulated as drugs rather than as cosmetics, which is why that data request is possible at all [s4].

The unresolved position is genuinely unresolved. The absorption is real and measured; the harm is unproven and unstudied; the benefit — the prevention of squamous cell carcinoma in randomised trials — is separately established [s3]. Anyone weighing that trade-off is weighing a known benefit against an uncharacterised risk, which is a different problem from weighing two known quantities, and the sources here are careful not to pretend otherwise.

This article is informational and is not medical advice.

Sources

• [s1] Effect of Sunscreen Application on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial — JAMA, 21 January 2020. https://doi.org/10.1001/jama.2019.20747
• [s2] Effect of Sunscreen Application Under Maximal Use Conditions on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial — JAMA, 7 May 2019. https://doi.org/10.1001/jama.2019.5586
• [s3] The efficacy and safety of sunscreen use for the prevention of skin cancer — CMAJ, 13 December 2020. https://doi.org/10.1503/cmaj.201085
• [s4] Sunscreen: How to Help Protect Your Skin from the Sun — US Food and Drug Administration, content current as of 9 June 2026. https://www.fda.gov/drugs/understanding-over-counter-medicines/sunscreen-how-help-protect-your-skin-sun