Trichomoniasis is a sexually transmitted infection (STI) caused by a tiny parasite called Trichomonas vaginalis (TV).

When to seek medical advice

Visit your GP or local genitourinary medicine (GUM) clinic if you experience any of the symptoms of trichomoniasis or if you think you may be infected.

Trichomoniasis can usually be diagnosed after an examination of your genital area and a laboratory test carried out on a swab taken from the vagina or penis.

If the test shows that you have trichomoniasis, it is important that your current sexual partner and any other recent partners are also tested and treated.

What causes trichomoniasis?

Trichomoniasis is caused by a tiny single-celled parasite (an organism that lives off another living being) called Trichomonas vaginalis.

In women, this parasite mainly infects the vagina and urethra (the tube that carries urine out of the body). In men, the infection most commonly affects the urethra, but the head of the penis or prostate gland (a gland near the bladder that helps produce semen) can become infected in some cases.

The parasite is usually spread by having unprotected sex (without using a condom), although it can also be spread by sharing sex toys. You do not have to have many sexual partners to catch trichomoniasis. Anyone who is sexually active can catch it and pass it on.

Trichomoniasis cannot be passed on through oral or anal sex, kissing, hugging, sharing cups, plates or cutlery, toilet seats or towels.

The best way to prevent trichomoniasis is to have safer sex. This means always using a condom when having sex, covering any sex toys you use with a condom, and washing sex toys after use.


Symptoms of trichomoniasis usually develop within a month of infection, although up to half of all infected men and women have no symptoms.

The symptoms of trichomoniasis are similar to those of many other sexually transmitted infections (STIs). Visit your GP or local genitourinary medicine (GUM) clinic if you develop any of the symptoms below.

Symptoms in women

Trichomoniasis mainly affects the vagina and urethra (the tube that carries urine out of the body) in women, causing any of the following symptoms:

  • abnormal vaginal discharge that may be thick, thin or frothy and yellow-green in colour
  • producing more discharge than normal, which may also have an unpleasant fishy smell
  • soreness, inflammation (swelling) and itching around the vagina – sometimes your inner thighs also become itchy
  • pain or discomfort when passing urine or having sex
  • pain in your lower abdomen (tummy)

Symptoms in men

Trichomoniasis mainly affects the urethra in men, although the foreskin, head of the penis and prostate gland (a gland near the bladder that helps produce semen) are occasionally affected.
The infection can cause any of the following symptoms:

  • pain during urination or ejaculation
  • needing to urinate more frequently than usual
  • thin white discharge from the penis
  • soreness, swelling and redness around the head of the penis and foreskin (balanitis)

Trichomoniasis is unlikely to go away without treatment. The infection may cure itself in rare cases, but you risk passing the infection on to someone else if you are not treated.


Trichomoniasis is usually treated quickly and easily with antibiotics.
Most people are prescribed an antibiotic called metronidazole which, if taken correctly, is very effective. You will usually have to take metronidazole twice a day, for five to seven days.

Sometimes this antibiotic can be prescribed in a single, larger dose. However, this may have a higher risk of side effects and it is not recommended for pregnant or breastfeeding women as a precaution.
Metronidazole can cause nausea, vomiting and a slight metallic taste in your mouth. It is best to take it after eating food. Contact your doctor for advice if you start vomiting because the treatment will not be effective if you are unable to swallow the tablets.

Do not drink alcohol while taking metronidazole and for at least 48 hours after finishing the course of antibiotics. Drinking alcohol while taking this medicine can cause more severe side effects.
A specialist can recommend alternative treatments if metronidazole is unsuitable for you (for example, if you are allergic to it).


If you take your antibiotics correctly, you will not normally need any follow-up tests or examinations for trichomoniasis.
However, if your symptoms remain or recur after treatment, or if your original laboratory test produced a negative result for trichomoniasis, you may require further testing to see whether your symptoms are being caused by a different sexually transmitted infection (STI).
If you have unprotected sex before your treatment is finished, you need to return to your GP surgery or sexual health clinic because you may have become reinfected. You must also return if you:

  • did not complete your course of antibiotics
  • did not take your antibiotics correctly (according to the instructions)
  • vomited shortly after taking your antibiotics

You may need more antibiotics or a different form of treatment.

Sexual partners

You should avoid having sex while you are being treated for trichomoniasis, as you may become reinfected.
If you were prescribed a single dose of antibiotics, you need to avoid having sex for seven days after you have taken the medication.

It is very important that your current sexual partner and any other recent partners are also tested and treated. If your sexual partner is not treated, this increases the risk of reinfection.

If you have had trichomoniasis and it has been treated, you will not be immune to the infection and you can get it again.

Like any sexually transmitted infection (STI), the best way to prevent trichomoniasis is to have safe sex. This means always using a condom.

The following measures will help protect you from trichomoniasis and most other STIs, including chlamydia and gonorrhoea. They will also help prevent you passing it on to your partner:

  • Use condoms (male or female) every time you have vaginal or anal sex.
  • If you have oral sex, cover the penis with a condom or the female genitals with a latex or polyurethane square (a dam).
  • If you are a woman and rub your vulva against your female partner’s vulva, one of you should cover your genitals with a dam.
  • Avoid sharing sex toys. If you do share them, wash them or cover them with a new condom before anyone else uses them.
  • If you are not sure how to use condoms correctly, read more about how to use a condom or call the FPA (see below) for advice.
  • If you have been diagnosed with trichomoniasis, make sure both you and your partner are treated, and that any sex toys you have used are cleaned.

Getting tested

If you are sexually active, go for regular sexual health check-ups. You can get an appointment by visiting your local genitourinary medicine (GUM) clinic. 
If you notice any signs or symptoms of an STI, avoid having sex and visit your GP or GUM clinic as soon as possible.