A new study showed that among patients with acne, taking daily doxycycline reduced the likelihood of acquiring a sexually transmitted infection (STI) by more than 25%. Rather than recommending doxycycline to modify risk for STI in people with acne, the authors said, “awareness of these effects may inform sexual health counseling for patients with acne, particularly adolescents and young adults.”

To determine whether doxycycline prescribed for acne correlates with reduced bacterial STI acquisition in the era of doxycycline postexposure prophylaxis (DoxyPEP), study authors enrolled 172,711 patients from the TriNetX network of deidentified electronic health records. Co-lead study authors included Richard J. Moraga, a third-year medical student at the Rosalind Franklin University of Medicine and Science in North Chicago, Illinois, and Hannah L. Cole, a fourth-year student at Harvard Medical School in Boston.

Patients were 15-45 years old and had an acne diagnosis code on the same date as an oral doxycycline prescription. Investigators searched for positive chlamydia, gonorrhea, or syphilis test results up to 180 days after the first doxycycline prescription among treated patients and an equal number of control participants with acne who had no prior exposure to doxycycline, sarecycline, or minocycline and were matched for age, sex, and other predictors of STI acquisition. Researchers excluded patients if their index event (first instance of doxycycline on the same date as an acne diagnosis, or, for control participants, first instance of acne diagnosis and comparator treatment) occurred more than 20 years before the analysis, which was conducted on August 29, 2025.

For doxycycline-treated patients, investigators found a composite STI acquisition hazard ratio (HR) of 0.73 (95% CI, 0.62-0.86), driven primarily by reduced chlamydia incidence (HR, 0.61; 95% CI, 0.50-0.75). Although HRs for gonorrhea (0.79) and syphilis (0.80) were directionally positive, they did not reach statistical significance. The brief report was published in the Journal of the American Academy of Dermatology on March 9.

Given doxycycline’s known antimicrobial activity and resistance patterns described in prior studies, Moraga and colleagues wrote their findings were biologically plausible. Perhaps doxycycline reduced overall STI acquisition, the authors surmised, because unlike episodic 200 mg DoxyPEP dosing, doxycycline treatment for acne involves continuous, variable-dose daily exposure more akin to the sustained administration of doxycycline preexposure prophylaxis (DoxyPrEP).

Real-World Snapshot

“It’s important that our study evaluates a broader, lower risk population receiving doxycycline for dermatologic indications because current CDC guidance supports DoxyPEP only for high-risk populations including men who have sex with men and transgender women, who are also more likely to undergo routine STI screening,” Moraga told Medscape Medical News.

Because most dermatologic patients are not routinely screened for STIs, study principal investigator John G. Zampella, MD, an associate professor of dermatology at New York University School of Medicine, New York City, added in an interview that the study “provides a clinical proof of concept demonstrating that the prophylactic benefits of doxycycline extend to patients receiving continuous treatment for acne.” But presently, he said, evidence is insufficient to support pivoting prescribing behaviors in dermatology to prevent STIs.

Considering the totality of evidence, including data from the DoxyPEP and DOXYVAC trials, Jason E. Zucker, MD, MS, an assistant professor of medicine at the Columbia University Medical Center, New York City, told Medscape Medical News that study reductions in composite STI and chlamydia incidence rates were impressive but unsurprising to STI specialists. He was not involved with the study.

Broaching the Sexual Health Discussion

However, Zucker said he hopes that the study creates a natural opening for sexual health conversations that dermatology has historically sidestepped. “For a 19-year-old on doxycycline for acne,” he said, “this gives the dermatologist real, evidence-based information to share in a way that feels organic to the visit rather than out of left field.”

Because dermatologists frequently see adolescents and young adults, Zucker said, dermatologists are “already far more involved in sexual healthcare than they may realize. Dermatologists are frequently the first clinicians to recognize syphilis, herpes simplex virus, and other STIs on the skin.”

As DoxyPEP enters the mainstream, added Zampella, the study provides context. “Dermatologists should be increasingly aware of the systemic secondary benefits — and potential public health implications — of the medications they routinely prescribe,” he said. “Dermatologists routinely manage various sexually transmitted infections; therefore, maintaining clinical expertise in DoxyPEP is a natural extension of the specialty’s scope.”

Avoiding False Reassurance

When counseling patients with acne, Zucker recommended saying that emerging evidence suggests that taking doxycycline may reduce the risk for certain bacterial STIs, particularly chlamydia and syphilis. However, he emphasized that doxycycline is no substitute for condoms, regular STI screening, vaccinations, or HIV preexposure prophylaxis. “The goal is to inform, avoid false reassurance, and use the visit as an opportunity to identify people who might benefit from more comprehensive sexual health services,” he said.

For patients at higher risk for STI or already taking DoxyPEP, Zampella said, “clinicians should be prepared to discuss how their continuous acne regimen may intersect with their sexual healthcare.” Although study findings suggest a significant protective benefit, he added, the study’s observational nature means that fully defining the efficacy of daily dermatologic doxycycline as a form of DoxyPrEP will require prospective trials.

The study authors reported no funding sources. Moraga and Cole reported having no disclosures. Zampella reported receiving honoraria from Dermavant Sciences, Janssen, Merck, Arcutis Biotherapeutics, and Ferndale Pharmaceuticals; and another study author reported receiving consulting fees from Honeydew Care and Sanofi Pasteur; both are unrelated to the study. Zucker reported having no relevant financial interests.

John Jesitus is a Denver-based freelance medical writer and editor.