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.
The first sign of syphilis is usually a small, painless sore called a chancre. It appears at the site where the bacteria entered the body — often on the genitals, but also on the anus, mouth or other areas that had direct contact with an infected partner. Because chancres are painless and often heal on their own, they are easy to miss. This is one reason syphilis can go undiagnosed for months or years.
Here’s how to recognise them.
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What Chancres Look Like
- Usually a single round or oval sore
- Firm, painless and with a clean base
- Ranges from small (a few millimetres) to about 2-3 cm
- May have slightly raised edges
- Often accompanied by nearby swollen lymph nodes
Chancres can look a bit like:
- An ulcer or open sore
- A small crater on the skin
- A firm painless lump before ulcerating
Where They Appear
| Location | Frequency |
|---|---|
| Penis (shaft, glans or foreskin) | Common in men |
| Anus or rectum | Common with receptive anal sex; may be internal and missed |
| Vulva or vagina | Common in women; internal chancres often missed |
| Cervix | Often not noticed |
| Mouth, lips or throat | With oral sex |
| Other skin sites | Rare |
Timing
- Appears 10-90 days after infection (average 3 weeks)
- Heals on its own within 3-6 weeks even without treatment
- The infection is not gone when the chancre heals — it has just moved to the next stage
Why Chancres Are Easily Missed
- They are painless — there’s no pain to draw attention
- Internal ones (vagina, rectum, cervix, throat) are often invisible
- They heal on their own, giving false reassurance
- Many people don’t associate a painless sore with an STI
What Else Could It Be?
A painful genital sore is more likely to be herpes than syphilis. Other possible causes include:
- Herpes (usually painful, often multiple blisters)
- Chancroid (painful ulcer, rare in UK)
- LGV (early painless ulcer, later painful lymph nodes)
- Trauma or skin conditions
Testing is the only reliable way to know.
What to Do
- Don’t self-treat or ignore a genital sore
- Contact a sexual health clinic promptly
- Testing includes a swab of the sore and a blood test for syphilis antibodies
- Treatment is highly effective — usually a single penicillin injection in early syphilis
- Partners from the last several months should be tested and treated
Treatment
Syphilis is curable with antibiotics:
- Primary and secondary syphilis — single injection of benzathine penicillin
- Late or unknown duration — three weekly injections
- Alternative antibiotics for penicillin allergy
Prompt treatment cures the infection and prevents long-term complications.
Read more: What is syphilis? | Cold sores vs syphilis | What is HIV?
Frequently Asked Questions
Is a syphilis sore painful?
No. Syphilis chancres are typically painless, which is one reason they are easy to miss.
Does the sore always appear?
Most people develop a chancre, but internal sores are often unseen. Some people report no sore at all and are first diagnosed at a later stage.
Can syphilis be cured?
Yes. A single injection of penicillin cures early syphilis. Later stages may need longer treatment.
Related reading
- Cold Sores vs Syphilis Sores: How to Tell the Difference
- Syphilis Symptoms by Stage
- Blood Test for Syphilis, Hepatitis B and Hepatitis C
- Can You Catch Syphilis Without Having Sex?
- Do STIs Always Have Symptoms?
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.
