What's In Your Sunscreen, Part3: Are Sunscreens Endocrine Disruptors?

Introduction

In a 2020 FDA-backed trial, six widely used sunscreen active ingredients—avobenzone, oxybenzone, octocrylene, homosalate, octisalate, and octinoxate—were shown to be substantially absorbed through the skin, with plasma levels exceeding the FDA’s safety threshold of 0.5 ng/mL after just a single full-body application (Matta MK et al., 2020). This raised renewed concerns that some chemical UV filters might act as endocrine-disrupting chemicals (EDCs) in humans.

Endocrine disruption refers to interference with hormone-regulated processes—either by mimicking, blocking, or altering the synthesis and metabolism of hormones. In this post, I review the current evidence on the potential endocrine-disrupting activity of each of these six ingredients. The focus is on human clinical and epidemiological data, particularly studies that evaluate systemic absorption and effects on sex and thyroid hormones, adrenal function, fertility, and developmental outcomes.

This is not intended to be a comprehensive systematic review.  Rather, it is a practical in-depth survey, guided by an emphasis on human studies—those that investigate direct impacts on living people—alongside a selection of the more compelling animal and laboratory findings that may offer mechanistic insights. One such study that stood out investigated human and rat cell assays to evaluate the endocrine-disrupting potential of the same six organic UV filters from the 2020 trial and found that, overall, these compounds exhibited low intrinsic biological activity in endocrine pathways . (Onyango et al., 2023) For most of the filters, any activity observed occurred at concentrations so high they caused cell death in addition to endocrine disruption. Only oxybenzone showed measurable endocrine activity below that threshold, and even then, the effects were limited.

Endocrine Activity In-Vitro of 6 UV Filters

(based on: Onyango et al., 2023)

UV Filter	Endocrine Activity Rank (1=highest)	Key Pathways Affected	Biological Relevance at Human Exposure
Oxybenzone	1	Estrogen, Androgen, Thyroid, Steroidogenesis	Yes – activity near max plasma levels, below cytotoxicity
Homosalate	2	Estrogen, Anti-Androgen	Unlikely – 100x above max plasma levels, some below cytotoxicity
Octocrylene	3	Anti-Androgen, Steroidogenesis	No – only above cytotoxicity
Avobenzone	4	Thyroid (weak)	No – only above cytotoxicity
Octisalate	5	Estrogen (weak)	No – only at very high concentrations
Octinoxate	6	None (no validated activity)	No – no activity observed

That said, as we will see some studies do report endocrine effects, especially in animal models or cell systems, and these findings shouldn’t be dismissed outright. However, they often involve exposures hundreds or thousands of times higher than what humans encounter through sunscreen. A simplified but helpful analogy: drinking eight glasses of water a day is healthy—trying to drink from a fire hose might be dangerous. The dose makes the difference, and that context is critical when evaluating laboratory findings.

At the same time, it’s important to recognize that we still don’t have a clear picture of the effects of long-term, low-dose exposure—particularly when considered alongside other chemical exposures people face daily. While current evidence doesn't indicate significant harm, the absence of evidence isn’t evidence of absence. A measured, cautious approach remains wise, especially as research continues to evolve.

Oxybenzone (Benzophenone-3)

Human Clinical Evidence

Oxybenzone, a broad-spectrum UVB/UVA filter, is one of the most studied sunscreen chemicals. Widespread human exposure is reflected by biomonitoring studies detecting oxybenzone (or its metabolite BP-3) in the urine of an estimated 97% or more of Americans, acquired mainly by the routine use of consumer products such as sunscreen, skin care lotion, lipstick, and hair spray. (Calafat et al, 2018; CDC NHANES survey)

Although there are numerous animal studies and laboratory evidence that oxybenzone can act as an endocrine disruptor, (Mustieles et al, 2023) human studies, when looked at collectively, have not corroborated a link between elevated oxybenzone levels and poor health outcomes. (Suh et al, 2020) This is not to say that evidence of harm cannot be found in human studies (as detailed below), but that there are studies with conflicting conclusions, both supporting or refuting the link.

• Sex Hormones in Males: Cross-sectional analyses of U.S. adults have linked higher oxybenzone exposure to 10-12% lower testosterone. (Tao et al, 2022) This aligns with an earlier report that adolescent boys with high BP-3 also had markedly reduced testosterone (~30–40% lower in the upper quartiles). (Scinicariello et al, 2016) These findings indicate a potential anti-androgenic effect of oxybenzone in males, but cross-sectional studies cannot prove causation and frequently mischaracterize variables as causal.

• Sex Hormones in Females: In adult women, oxybenzone alone did not correlate with dysfunction but in multi-chemical models, oxybenzone was associated with lower FSH and LH levels. (Pollack et al, 2017) It may also have modest effect at impacting fertility in younger (<35 year old) women. (Silva et al, 2024)

• Thyroid Function: Several studies have evaluated oxybenzone’s impact on thyroid hormones, with somewhat inconsistent results. A population level study showed a relationship between higher urinary oxybenzone and lower thyroid hormone levels. (Kim et al, 2017) However, this is not consistent across all studies. (Suh et al, 2020) For example, no biologically significant changes in thyroid hormones were identified after a week of daily whole-body application of sunscreen containing oxybenzone. (Janjua et al., 2007)

• Reproductive and Developmental Outcomes: Thus far, large prospective studies have not found strong links between oxybenzone and fertility or birth outcomes. (Suh et al, 2020) However, a single case-control study detected an increased link (1.65 times greater likelihood) between oxybenzone exposure and endometriosis. (Kunisue et al, 2012) Research on pubertal development has yielded mixed findings, with some showing small associations with earlier puberty, (Binder et al, 2018) and some small associations with delayed puberty. (Wolf et al, 2015) It’s necessary to emphasize that not every study finds an negative effect o effect – for instance, a controlled trial in 32 humans applying sunscreen containing oxybenzone and two other UV filters over 4 days found no significant changes in reproductive hormones such as testosterone, FSH, or LH. (Janjua et al, 2004)

Human In Vitro Evidence

• In vitro studies show effects on sperm cell function. (Rehfeld et al, 2016)

• It was also demonstrated to be the most active and potent endocrine disruptor of all the UV filters discussed here. (Onyango et al, 2023)

Animal Studies

• Oxybenzone exposure at levels that overlap with human peak plasma levels led to prolonged estrous cycles, changes in uterine estrogen receptor gene expression, endometrial hyperplasia, and altered mammary gland development in rodents. (Mustieles et al., 2023)​

• Oxybenzone (BP-3) and its metabolite BP-1 increased with dose and were found to accumulate in thyroid, adrenal, and thymus tissues. The impact on these tissues over time is not clear. (Mustieles et al, 2023).

Homosalate

Human Clinical Evidence

There are no epidemiological or clinical studies in humans conclusively demonstrating endocrine disruption from homosalate. However, unlike oxybenzone and similar to octocrylene, homosalate is not commonly measured in urine, so population-level correlations are lacking. To date, no controlled trial has reported on sex hormone or thyroid changes due to homosalate application. The main human-relevant evidence comes indirectly.

Human In Vitro Evidence

• The same in vitro study that showed sperm cell dysfunction when exposed to oxybenzone and octocrylene showed the same for homosalate. (Rehfeld et al, 2016)

• In vitro, homosalate increased the expression of thyroid-specific genes in human thyroid cells at sub-cytotoxic concentrations. (Coperchini et al., 2024)

Animal Studies

Animal studies have provided some hints that homosalate may act as an endocrine disruptor, although results are somewhat mixed:

• Estrogen/Androgen Activity: Homosalate has shown some estrogenic and anti-androgenic effects in rodent models, but findings have been inconsistent and generally weak. In one study, high-dose dermal exposure during prenatal development was associated with reduced testosterone levels and increased LH and FSH in male rats, though without consistent changes in reproductive organ weights or histopathology. In female rats, homosalate exposure altered hormone levels and follicle counts at certain developmental stages, but did not significantly affect uterus weight, puberty onset, or histopathology. (Erol et al, 2017)

• Thyroid Effects: In rats, high-dose exposure during development was associated with increased thyroid weight and altered thyroid hormone levels in some groups, though without consistent histopathological changes or functional impairment. (Erol et al., 2017)

Octocrylene

Human Clinical Evidence

There is currently little direct human data on octocrylene’s endocrine effects. No epidemiological studies have definitively linked octocrylene exposure to altered hormone levels or clinical endocrine disorders. This may be partly because biomarkers of octocrylene exposure are less commonly measured in large cohorts (it is not included in NHANES and I did not find it measured frequently in other fertility, hormone, or thyroid studies.) Thus, our understanding of octocrylene in humans relies primarily on indirect evidence.

Human In Vitro Evidence

• Did not show a progesterone-like impact on sperm cell dysfunction. (Rehfeld et al, 2016)

Animal Studies

• In toxicological animal studies, octocrylene has shown some signs of endocrine activity, though not as overtly as oxybenzone or octinoxate. It also occurs in the context of VERY high-doses of octocrylene that do not mimic real-world use patterns. (I was not able to access the primary literature cited in this report)

• Overall, it appears that octocrylene has low intrinsic biological activity in endocrine-related assays, and predicted risk of human endocrine disruption is low due to the large margin between in vitro active concentrations and actual human plasma levels. (Onyango et al, 2023)

• Interestingly, octocrylene has been identified as a potential metabolic disruptor that could lead to obesity. (Ko et al, 2022) However, tested concentrations were 25–1000 times greater than typical human plasma levels.

Avobenzone

Human Clinical Evidence

Direct human studies on avobenzone’s endocrine effects are very sparse. No clinical trials or epidemiological studies to date have specifically linked avobenzone exposure to changes in sex or thyroid hormones or to reproductive outcomes in humans.

Human In Vitro Evidence

• A lab-based study reported that avobenzone exposure could impact placental cells, suggesting it might adversely affect early pregnancy. (Yang et al, 2018)

Animal Studies

• A study in zebrafish (a common animal model for endocrine studies) found that avobenzone tested at environmental concentrations can reduce thyroxine (T4) levels and alter expression of thyroid-regulating genes. (Ka and Ji, 2022)

  
  

Octisalate

Human Clinical Evidence

No human studies have specifically implicated octisalate in endocrine disruption. It is one of the least studied in this regard. There are no reports linking octisalate to changes in sex hormones, thyroid function, fertility, or developmental outcomes in people. In fact, a review by the Australian Cancer Council concluded that “there is no evidence of any sunscreen chemicals used in Australia (including octisalate) disrupting the endocrine system in humans,” although this includes every ingredient we have discussed and will discuss in this blog post, in addition to many others including aminobenzoic acid (PABA).

Human In Vitro Evidence

• Octisalate was among three of the six UV filters we are focusing on that show a progesterone-like effect on sperm cells. (Rehfeld et al, 2016) Beyond the sperm finding, I did not find notable published animal studies of octisalate causing endocrine outcomes.

•  In computational and high-throughput screens, octisalate tends to rank low in estrogenic or androgenic activity. (Onyango et al, 2023)    

Animal Studies

• Octisalate has not shown significant endocrine activity in animal studies, although data are relatively sparse.

Octinoxate (OMC)

Human Clinical Evidence

Direct human data on octinoxate’s endocrine effects are limited. Unlike oxybenzone, octinoxate has not been extensively studied in epidemiological cohorts, so we lack large-scale correlations with hormone levels or health outcomes.

• In one small study, no biologically significant changes in thyroid hormones were identified after a week of daily whole-body application of octinoxate. (Janjua et al., 2007)

• In a similar study, octinoxate is systemically absorbed through the skin after whole-body application of a sunscreen containing 10% octinoxate, with peak plasma concentrations reaching up to 20 ng/mL in men and 10 ng/mL in women​ (higher than what was found in the impactful JAMA paper), but also found no biologically meaningful changes in reproductive hormone levels (e.g., FSH, LH, estradiol, testosterone).

• To date, no epidemiological study has clearly linked octinoxate to fertility issues or developmental outcomes in humans.

Human In Vitro Evidence

• Octinoxate (OMC) demonstrated estrogenic activity in human breast cancer cells in vitro. (Schlumpf et al, 2001)

• Minimal endocrine activity at concentrations relevant to human exposure. (Onyango et al. 2023)

Animal Studies

• Estrogenic Activity: Demonstrated estrogenic activity in female rat uteruses, albeit with weak effects after very high dose administration of octinoxate. (Schlumpf et al, 2001)

• Anti-Androgenic and Other Hormone Effects: In rats, large quantity oral octinoxate exposure during gestation and lactation caused delayed male puberty, reduced sperm counts, and altered reproductive organ weights. It also led to increased pituitary weights and hormone alterations in both sexes, suggesting endocrine-disrupting potential through interference with the hypothalamic-pituitary-gonadal axis. (Axelstad et al, 2011)

• Thyroid Disruption: A trout study showed that 6-week dietary exposure to octinoxate altered thyroid hormone regulation in fish (e.g., reducing circulating T4). (Cahova et al, 2023)

There are seemingly divergent findings here that require context to reconcile. Onyango et al. approached the question from a pharmacokinetic and exposure-relevant angle, asking: “Are the concentrations that show endocrine activity in lab tests ever reached in human plasma after sunscreen use?” For octinoxate, their answer was no—bioactivity in their dataset occurred only at concentrations far exceeding those found in real-world human plasma, with the exception of oxybenzone.

Meanwhile, animal and in vitro studies provide a different lens—they explore what could happen under extreme or sustained exposure conditions, not necessarily what does happen with routine sunscreen use. This is an important distinction.

It's not that one set of studies is right and the other is wrong—they are answering different questions. The Axelstad, Schlumpf, Cahová, and Lorigo studies collectively suggest that “OMC can disrupt hormone systems at high or chronic exposure levels in animals.”  In contrast, Onyango et al. essentially respond: “Yes—but those levels aren’t achieved in humans using sunscreen normally.”

So, when interpreted together, the weight of current evidence suggests that octinoxate poses a low risk of endocrine disruption in humans under typical use conditions. This conclusion likely also applies to many of the other UV filters on this list. Still, the theoretical risk at higher or cumulative exposures, especially in vulnerable populations, means that further human-focused studies would be prudent.

Conclusion

Even though it is best for clicks and traffic to make bold if not controversial statements, I try to temper my conclusions based on the available evidence and layer in appropriate amounts of common sense when approaching these difficult topics. Unlike some who are quick to label these sunscreen ingredients as hormone disruptors, I think it's premature to conclude that these ingredients are likely to cause you harm when used appropriately.

The exception may be oxybenzone, which stands out because of its ubiquity in biomonitoring studies, and the relative abundance of human clinical and epidemiologic data associating it with modest changes in hormone levels.  In vitro and animal studies further support its higher endocrine bioactivity compared to the other UV filters reviewed, although most human-relevant effects still occur at exposure levels exceeding real-world use. While not definitive, the cumulative body of evidence places oxybenzone at the higher end of concern. However, oxybenzone has been largely phased out of most common sunscreens sold in the US.

Homosalate and octocrylene occupy a middle ground: human data are limited or lacking, but both show some in vitro endocrine-related effects (e.g., on sperm cells, thyroid gene expression), and animal studies suggest potential for mild estrogenic, anti-androgenic, or thyroid effects – again, generally at very high doses. These findings warrant a degree of caution but do not, in my view, justify dramatic action. Real-world human exposure levels remain far below thresholds shown to induce effects in experimental models.

Avobenzone and octisalate appear to be the lowest-risk among the six UV filters reviewed. Neither has been linked to endocrine disruption in humans, and the experimental studies that do exist suggest weak or absent bioactivity under real-world conditions. Octisalate in particular has little compelling evidence of endocrine activity from any source, although that may partly reflect a lack of study rather than conclusive proof of safety.

Octinoxate stands out as something of an outlier among the six UV filters reviewed. Compared to avobenzone and octisalate, it shows more substantial evidence of endocrine-disrupting potential, but primarily in animal models and in vitro studies. At high doses, octinoxate has demonstrated estrogenic, anti-androgenic, and thyroid-disrupting activity. However, it was also identified by Onyango et al. (2023) as having minimal endocrine activity at concentrations relevant to human exposure.

In short, while none of these UV filters can be declared definitively “endocrine safe” or “endocrine harmful,” the weight of evidence suggests that oxybenzone carries the most potential for endocrine effects, followed by homosalate and octocrylene, and avobenzone and octisalate posing the lowest relative concern. Octinoxate is harder to define, but probably lays at the lower end of the spectrum in terms of risk potential.

Overall, choose your sunscreen based on your goals and risk tolerance. If you are concerned about endocrine disruption and engage in daily widespread application of sunscreen, there are many alternatives to chemical UV filters including zinc oxide or titanium dioxide, sun protective clothing, and shade-seeking, allowing you to completely avoid any potential risk, as low as it may be. If you use sunscreen in a more targeted fashion and prefer the cosmetic elegance of many of these chemical blockers, there is no indication that they pose a significant risk to your health.

Dr. Ryan M. Trowbridge, MD, MS, MA

Harvard-Trained, Board-Certified Dermatologist and DermMythBuster

P.S. Have you come across any new or conflicting research on this topic? Please share—I’d love to explore it further with you!

For medical consultations with me, visit Bridge-Derm.com.

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