A New STI? The Animal Skin Infection Popping Up in European Saunas

If you spend time around livestock or horses, you might already be familiar with conditions like "rain rot", "mud fever", or "lumpy wool". These are all common names for dermatophilosis, a distinct skin infection caused by the bacterium Dermatophilus congolensis.

Historically, this has been known strictly as an animal disease that occasionally jumps to farmers or veterinarians. However, public health data has revealed an unprecedented shift: the bacteria is now spreading human-to-human in major urban areas.

Popular medical content creators, including Dr Carlton (@doctorcarlton) on TikTok a prominent LGBTQ+ health advocate, has been raising awareness about clusters of this infection popping up in places you would least expect them, thousands of miles away from the nearest farm.

Here is what you need to know about this unusual outbreak, how it presents, and why it is catching the attention of sexual health clinics.

The Shift: From Farm to Sauna

According to official briefings from the European Centre for Disease Prevention and Control (ECDC), medical teams in France, Spain, Germany, and Sweden have identified clusters of human-to-human dermatophilosis [1].

The vast majority of these cases have been diagnosed among gay, bisexual, and other men who have sex with men (MSM) [1]. Crucially, none of the patients had any contact with infected livestock. Instead, genomic testing and patient interviews revealed a common denominator: visiting adult leisure saunas, public spas, and sex-on-premises venues in cities like Lyon, Paris, and Barcelona [1, 2].

Why Saunas?

The transmission perfectly aligns with how Dermatophilus congolensis thrives. The bacteria depend heavily on two things: moisture and microtrauma.

The hot, wet, and highly humid atmosphere of a communal sauna or steam room provides the ultimate playground for the bacteria's swimming zoospores (the active, mobile form of the bacteria) [1]. When combined with close, skin-to-skin physical contact and the minor friction or micro-abrasions that occur during sexual activity, the bacteria can easily cross directly from one person's skin to another [1, 3].

While this marks a brand-new transmission pathway, experts are hesitant to label it a permanent "new STI" just yet, it is a skin-to-skin pathogen using high-contact, high-humidity environments to spread. In fact, similar small clusters have also been found in entirely non-sexual, highly physical environments, such as martial arts clubs in Norway where athletes share close skin contact [1].

Recognising the Symptoms

Because it is relatively rare in humans, the clinical picture can vary widely and is frequently mistaken for more common conditions like ringworm, herpes, or standard bacterial folliculitis (inflamed hair follicles) [3].

In these recent sauna-linked clusters, the symptoms mirror the classic presentation but are focused entirely on the areas of physical exposure:

Initial Signs: Small, itchy, or slightly tender red bumps (papules) and pus-filled blisters (pustules).

Progression: The blisters rupture to form oozy, scaly, or crusted yellowish-brown scabs.

Common Sites: In the current outbreak, lesions are predominantly showing up on the genitals, lower abdomen, thighs, groin, and occasionally the face/beard area [1, 3].

Sensation: Mild burning or itching, but usually free from severe pain or systemic symptoms like fever [1].

Diagnosis and Treatment.

If you notice an unusual, crusty rash after visiting a public spa or venue, a proper medical diagnosis is essential. A healthcare professional will typically take a swab or a scraping of the lesions to perform a microscopic analysis or culture the sample [3]. Under a microscope, the dividing cells look distinctly like parallel rows of miniature train tracks a classic giveaway for microbiologists.

The Silver Lining: While public health experts note that the sudden spread through a tight social network feels reminiscent of the early stages of the 2022 mpox outbreak, they emphasise that dermatophilosis is far less severe [1]. It remains entirely localized to the skin, causes no systemic illness, and clears up rapidly.

The infection is highly treatable:

Self-Limiting: In many individuals with robust immune systems, mild cases can resolve on their own once the skin is kept clean and dry [1].

Antibiotics: For persistent or widespread lesions, standard courses of common oral or topical antibiotics (such as amoxicillin, doxycycline, or cloxacillin) clear the infection completely and quickly [1, 2].

Venues and saunas in affected regions are currently being advised by public health bodies to reinforce routine surface hygiene measures to minimize any risk of indirect transmission via contaminated surfaces [1].

Sources & Medical Literature

[1] European Centre for Disease Prevention and Control (ECDC) (June 2026). Rapid Risk Assessment: Clusters of dermatophilosis in five EU/EEA countries in 2025–2026. ECDC Technical Report

[2] Degreze, M., et al. (2026). Suspected sexual transmission of dermatophilosis among men who have sex with men, Lyon and Paris, France, 2025–2026. Emerging Infectious Diseases (CDC).

[3] Descalzo, V., et al. (2026). Suspected sexual transmission of dermatophilosis among men who have sex with men, Barcelona, Spain, 2025–2026. Emerging Infectious Diseases (CDC).