References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Several STIs can cause skin rashes as part of their symptoms. The most notable are syphilis, HIV (during seroconversion) and herpes. Rashes can also appear as a side effect of STI medications. Most rashes are not caused by STIs, but some rash patterns in the right context warrant prompt testing.
Here’s what to know.
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STIs That Can Cause Rashes
| STI | Rash Pattern | Timing |
|---|---|---|
| Syphilis (secondary stage) | Non-itchy rash on palms and soles; widespread body rash | Weeks to months after chancre |
| HIV (seroconversion) | Mild pink rash on trunk; often with fever and flu-like symptoms | 2-4 weeks after exposure |
| Herpes | Cluster of painful blisters; genital, oral or elsewhere | Variable — weeks to years after exposure |
| Scabies | Very itchy rash with tiny tracks | 2-6 weeks after contact |
| Pubic lice | Itching at the site of infestation | Days to weeks |
| Genital warts | Small flesh-coloured growths, not a rash exactly | Weeks to months |
Secondary Syphilis Rash
The classic syphilis rash is one of the most distinctive in medicine:
- Non-itchy (unlike most rashes)
- Often affects the palms of the hands and soles of the feet — rare in other conditions
- Can be widespread across the body
- Appears weeks to months after the original chancre has healed
- Can come and go
- Often accompanied by fever, fatigue, sore throat and swollen lymph nodes
A rash on the palms and soles in a sexually active adult should prompt urgent syphilis testing.
HIV Seroconversion Rash
Around 70-80% of people with HIV experience seroconversion illness 2-4 weeks after infection. A mild pink or red rash on the trunk is one of the common features. It’s usually:
- Not itchy or mildly itchy
- Accompanied by fever, sore throat and swollen lymph nodes
- Lasts 1-2 weeks and resolves
Easy to mistake for viral illness or drug reaction — which is one reason acute HIV often goes undiagnosed.
Drug Rashes from STI Medications
Several medications used for STIs can cause rashes:
- Penicillin and related antibiotics — allergic rashes
- Doxycycline — photosensitivity
- HIV medications — particularly nevirapine and abacavir
- Co-trimoxazole — can cause allergic reactions
Serious drug rashes with fever, blistering or mouth sores need urgent medical attention.
When to Seek Help
- Rash with fever or feeling unwell
- Widespread body rash
- Rash on palms and soles
- Painful blisters in genital or oral areas
- Rash after a new sexual encounter
- Rash after starting new medication
- Rash with blistering, mouth sores or peeling skin — medical emergency
Investigation
Your clinician will take a history, examine the rash and decide on tests. For STI-related rashes, tests may include:
- Blood test for syphilis and HIV
- Swab of blisters for herpes
- Scraping for scabies
Read more: Skin problems and HIV | Is my rash HIV? | What is syphilis?
Frequently Asked Questions
What does a syphilis rash look like?
Typically a non-itchy rash on the palms and soles, sometimes widespread. It appears weeks to months after the initial painless sore (chancre).
Can every STI cause a rash?
No. Chlamydia, gonorrhoea, trichomoniasis and others don’t cause rashes. Syphilis, HIV, herpes and some medications are the main STI-related rash causes.
Should I test for STIs if I have an unexplained rash?
If you’ve had risky sexual exposure recently or the rash has typical STI features (palms and soles, painful blisters, fever), yes.
Related reading
- Abnormal Genital Discharge and Chlamydia
- Asymptomatic STIs: Silent Infections Explained
- Causes of Painful Sex and How to Treat It
- Cold Sores vs Syphilis Sores: How to Tell the Difference
- Common STI Symptoms in Women
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
