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.
Cold sores (caused by herpes simplex virus, usually HSV-1) and syphilis sores (chancres) can both appear around the mouth and lips. But they have important differences in appearance, behaviour and cause. Knowing the difference helps you decide when to seek testing.
Here’s a clear comparison.
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Key Differences
| Feature | Cold Sore (Herpes) | Syphilis Chancre |
|---|---|---|
| Cause | HSV-1 (sometimes HSV-2) | Treponema pallidum bacteria |
| Pain | Usually painful, burning, tingling | Painless |
| Appearance | Cluster of small blisters that burst and crust | Single round, firm sore with clean base |
| Typical location | Lip edges | Anywhere contact was made |
| Duration | 5-14 days | 3-6 weeks if untreated |
| Recurring? | Often — can come back many times | Primary chancre appears once |
| Triggered by? | Stress, illness, sunlight | Not reactivation — fresh infection |
Cold Sores in Detail
Cold sores are caused by HSV-1 (occasionally HSV-2). Key features:
- Start with tingling or burning on the lip
- Develop into a cluster of small blisters
- Blisters burst, ooze, then crust over
- Heal completely in 1-2 weeks
- Can recur when triggered by stress, illness, sunlight or hormonal changes
- Very common — most adults carry HSV-1
Syphilis Chancres in Detail
Syphilis chancres are caused by the bacterium Treponema pallidum. Key features:
- Painless, which is distinctive
- Usually a single sore (sometimes more)
- Round or oval, firm, with a clean base
- Appears at the site of infection — could be lips, mouth, genitals, anus
- Heals on its own in 3-6 weeks, even without treatment
- Doesn’t mean the infection is gone — it has just moved to the next stage
When You Can’t Tell
Sometimes the difference isn’t obvious, particularly early in the course. If you have any doubt, especially with a recent new sexual partner, testing is the right move. Syphilis testing is:
- Straightforward (blood test)
- Available at sexual health clinics
- Free on the NHS
Treatment
Cold sores
- Often heal on their own
- Topical or oral antivirals (aciclovir) speed healing
- Cream or tablets available from pharmacies
Syphilis
- Single injection of benzathine penicillin cures early syphilis
- Alternative antibiotics for penicillin allergy
- Late or complicated syphilis needs longer treatment
When to See a Doctor
- A sore on the lip or mouth that doesn’t heal in 2 weeks
- A painless oral or genital ulcer
- Recurring sores with a recent new sexual partner
- Sores accompanied by swollen lymph nodes, rash or fever
- Any unexplained oral ulcer in a sexually active person
Read more: Identifying syphilis sores | What is herpes? | What is syphilis?
Frequently Asked Questions
Can I tell cold sores and syphilis apart by appearance?
Usually pain is the biggest clue — cold sores hurt, syphilis chancres don’t. But appearance isn’t always reliable. Testing gives certainty.
Is a painless mouth sore always syphilis?
No. Other causes include aphthous ulcers and minor trauma. But a new painless ulcer after a sexual encounter should be tested.
Do syphilis sores come back?
The primary chancre appears once. Later stages of untreated syphilis can cause different skin signs, but not repeated chancres like cold sores.
Related reading
- How to Identify Syphilis Sores (Chancres)
- Lab Test for Syphilis and Herpes
- Syphilis Symptoms by Stage
- Blood Test for Syphilis, Hepatitis B and Hepatitis C
- Can You Get Herpes From a Toilet Seat?
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.
