It’s a question people don’t often ask out loud, but it’s an important one. If you or your partner have a mouth ulcer and go on to have oral sex, can it cause an infection in the genital area? Is that considered an STI? And what should you do next?
Let’s break it down clearly and honestly.
What is a mouth ulcer?
A mouth ulcer is a small, sometimes painful sore that can appear on the inside of the mouth, lips, or tongue. They’re usually caused by things like:
- Minor injury (e.g. biting your cheek)
- Stress
- Certain foods
- Vitamin deficiencies
- Infections like herpes simplex virus (HSV)
Most mouth ulcers are harmless and clear up on their own in a week or two. But if the ulcer is caused by an infection, like oral herpes or syphilis, that’s when you need to be more cautious. There are also some skin conditions that cause oral sores.
Can a mouth ulcer lead to a genital infection?
If the mouth ulcer is just from irritation or a canker sore, no, it’s not contagious and won’t spread to the genitals.
However, if the ulcer is caused by oral herpes (HSV-1), and you perform oral sex on someone, there is a risk of passing the virus to your partner’s genitals. That would result in genital herpes, which is considered a sexually transmitted infection (STI).
So in short:
- A non-infectious mouth ulcer? No STI risk.
- A herpes-related ulcer? Yes, it can transmit HSV-1 to the genitals.
What does that mean for you or your partner?
If you’re not sure what’s caused the ulcer, or it keeps coming back, it’s a good idea to get it checked by a healthcare provider.
If you know you have oral herpes:
- Avoid oral sex when you have a visible sore or feel a tingle (signs of an outbreak).
- You can reduce the risk of transmission with condoms, dental dams, and antiviral medication if prescribed.
If you think you may have been exposed:
- Keep an eye out for any unusual symptoms, such as tingling, redness, small blisters or sores on the genitals.
- Visit a sexual health clinic if you’re worried or notice any changes – even if it’s just for reassurance.
Is genital herpes serious?
While genital herpes is a lifelong condition, it’s more common than people think — and often manageable. Many people with herpes have mild symptoms (or none at all), and treatment can help reduce outbreaks and lower the chance of passing it on. Some the signs and symptoms include:
- Small blisters or sores on the genitals, anus, thighs, or buttocks
- Itching, tingling, or burning before the sores appear
- Pain when peeing (especially if urine touches the sores)
- Flu-like symptoms (fever, aches) during the first outbreak
The most important thing is to not panic. Herpes is surrounded by a lot of myths and stigma, but it’s very possible to live a healthy, full sex life with the right support and information.
Final thoughts
If you or your partner have a mouth ulcer and are unsure what caused it, it’s always okay to press pause on oral sex until you know more. Saliva can carry infections like herpes, and taking care of your sexual health means being aware of these risks – and knowing where to turn if you need support.
Need advice or testing?
Essex Sexual Health Service offers free, confidential testing, treatment and support. Whether you have symptoms, want peace of mind, or just have questions – we’re here to help.
Find your local clinic or order a free STI test kit online →
