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.
A red sore on the penis can be alarming but has many possible causes — not all of them STIs. Herpes, syphilis, balanitis, friction and skin conditions can all produce red sores. The key is to get it assessed rather than guessing, especially if it appeared after sexual contact.
Order a discreet home STI test
Possible Causes
| Cause | Features |
|---|---|
| Herpes | Painful blisters that burst into ulcers |
| Syphilis chancre | Single painless firm ulcer |
| Balanitis | Red, inflamed glans; discharge under foreskin |
| Friction/trauma | Soreness after vigorous sex; heals quickly |
| Folliculitis | Red bumps around hair follicles |
| Psoriasis/eczema | Dry, red, flaky patches |
| Genital warts | Flesh-coloured growths (not usually sores) |
When to Seek Help
- Any sore after a new sexual partner
- Painless ulcer (could be syphilis)
- Painful blisters (could be herpes)
- Sore not healing in 2 weeks
- Fever or swollen glands alongside
Testing
- Swab from the sore (herpes PCR, syphilis PCR)
- Blood test for syphilis
- STI screen for chlamydia, gonorrhoea, HIV
Treatment
- Herpes — antiviral medication
- Syphilis — penicillin injection
- Balanitis — antifungal or gentle hygiene
- Friction — rest and lube next time
Read more: What looks like herpes | Syphilis sores | Balanitis
Frequently Asked Questions
Is a red sore always an STI?
No — many non-STI causes exist.
Should I test?
If it appeared after sexual contact, yes.
Can I treat it at home?
Not until the cause is identified. See a clinician.
Related reading
- Common STI Symptoms in Women
- Is Testicular Pain a Sign of an STI?
- Abnormal Genital Discharge and Chlamydia
- Asymptomatic STIs: Silent Infections Explained
- Causes of Painful Sex and How to Treat It
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.
