Trichomonas vaginalis

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


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

It can be difficult to diagnose trichomoniasis because there may not be any symptoms. When there are symptoms, they can be similar to those of other sexually transmitted infections (STIs).

Women are more likely to have symptoms than men. They may have soreness and itching around the vagina and a change in vaginal discharge, while men may experience pain after urination and ejaculation.

See your doctor if you experience any of the symptoms of trichomoniasis or if you know you’ve been exposed to it.

If you do not want to see your doctor, go to your local genitourinary medicine (GUM) clinic, where they will be able to test and treat your infection.

What causes trichomoniasis?

Trichomoniasis is caused by a tiny single-celled parasite (lives off another living being) called Trichomonas vaginalis. It is a single-celled organism that latches onto the lining of the vagina.

The parasite is usually spread by having unprotected sex (without using a condom). 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.

In rare cases, the infection can be spread by sharing sex toys. However, using a condom to cover your sex toy and washing it after use should decrease the chances of the infection spreading.

Treating trichomoniasis

Trichomoniasis is unlikely to go away without treatment. Most men and women are treated with an antibiotic called [metronidazole], which is very effective. People who cannot take metronidazole may be prescribed a different medication.

It is important to complete the whole course of antibiotics and avoid sexual intercourse until the infection clears up to prevent reinfection.

Read more information about treating trichomoniasis.

Complications of trichomoniasis

Complications are rare with trichomoniasis.

However, the infection can sometimes weaken the barrier of mucus in the cervix (the neck of the womb). This mucus barrier helps protect women from developing infection in their reproductive organs. If the mucus is weakened, this increases your risk of developing HIV.

It is therefore very important to practise safe sex by always using a condom.

Read more information about preventing trichomoniasis.


If you develop trichomoniasis while you are pregnant, your baby may be at risk of developing complications. Trichomoniasis may cause your baby to be born prematurely, or to have a low birth weight.


Trichomoniasis is thought to be very common, but many men and women with it have no symptoms. Women are more likely to have symptoms of trichomoniasis than men.

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

Symptoms in women

Trichomoniasis affects the vagina and urethra (tube through which urine passes), causing any of the following symptoms:

  • soreness, inflammation (swelling) and itching around the vagina – sometimes your inner thighs also become itchy
  • vaginal discharge that appears thicker, thinner, frothy or yellow–green in colour
  • producing more discharge than normal, which may also have an unpleasant fishy smell
  • pain or discomfort when passing urine
  • discomfort during sexual intercourse
  • pain in your lower abdomen (tummy)

Symptoms in men

Trichomoniasis affects the urethra (the tube through which urine passes) and occasionally the prostate gland (a gland at the neck of the bladder that helps produce semen), causing any of the following symptoms:

  • pain after urination and ejaculation
  • thin white discharge from the penis
  • discomfort during sexual intercourse


Trichomoniasis can sometimes be difficult to diagnose because symptoms are similar to those of other sexually transmitted infections (STIs).

If you do not want to see your doctor, go to your local genitourinary medicine (GUM) clinic, where they will be able to test and treat your infection. Find your nearest sexual health clinic.


If your doctor or nurse suspects you have trichomoniasis, they will usually carry out an examination of your genital area.

In women, trichomoniasis may cause red blotches on the walls of the vagina and on the cervix (the neck of the womb).

If you are a man with suspected trichomoniasis, your doctor or nurse will examine your penis for signs of inflammation.

Laboratory testing

After your physical examination, your doctor or nurse may need to take a swab from either the vagina or penis so that it can be tested for the trichomoniasis infection. The swab will be sent to a laboratory for analysis. It may take several days for the results to come back.

If your doctor or nurse strongly suspects that you have trichomoniasis, you may be advised to begin a course of treatment before your results come back. This will ensure that your infection is treated as soon as possible and reduces the risk of the infection spreading.

Sometimes, the result of a routine smear test may report that "organisms consistent with Trichomonas vaginalis have been seen". This does not necessarily mean that you have trichomoniasis, so do not assume that you have a sexually transmitted infection (STI) until further tests have been done.

In men, a urine sample can also be tested for trichomoniasis.

Notifying sexual partners

If the test shows that you have trichomoniasis, it is very important that your current sexual partner and any other recent partners are also tested and treated. The staff at the clinic or general practice can discuss with you which of your sexual partners may need to be tested.

You may be given a contact slip to send or give to your partner or partners or, with your permission, the clinic can do this for you. The slip explains that they may have been exposed to an STI and suggests that they go for a check-up. It may or may not say what the infection is. It will not have your name on it, so your confidentiality is protected.

This is called partner notification. You are strongly advised to tell your partner or partners, but it is not compulsory.

If you have had trichomoniasis and been cured, there is no need to tell any future partners that you had it.


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

If there is a high chance you have trichomoniasis and you have obvious symptoms, treatment may be started before the results of the test are back.

Antibiotics and antifungals

Trichomoniasis is usually treated quickly and easily. Most people will be prescribed an antibiotic known as [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 concentrated dose. However, this single dose is not suitable for pregnant or breastfeeding women.

Metronidazole can cause nausea, vomiting and a slight metallic taste in your mouth. It is best to take it after eating food. If you start vomiting, contact your doctor as the treatment will not be effective.

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.

If you cannot tolerate metronidazole, your doctor may prescribe a single dose of another antibiotic called [tinidazole].

Pregnant women

Pregnant women can safely take metronidazole.

However, pregnant women who have side effects when taking metronidazole or who have concerns should discuss this with their doctor.

A clotrimazole pessary is a type of antifungal medicine that is inserted into the vagina. It is very safe for pregnant women to use and will help relieve symptoms of trichomoniasis.

However, it is far less effective than antibiotics and is unlikely to cure the infection. Your doctor will have to monitor your condition and may need to carry out further tests to check the infection has cleared.

Follow-up tests

If you take your antibiotics correctly, you will not normally need any follow-up tests or examinations for trichomoniasis.

However, if your symptoms remain 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 doctor's 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

Don't have sexual intercourse while you are being treated for trichomoniasis, as you may become reinfected.

If you were prescribed a single one-day dose of antibiotics, you need to avoid sexual intercourse for seven days after you have taken the medication.

It is also important that your partner is tested for the infection, as they too must be 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 HIV, chlamydia and gonorrhoea. They will also help prevent you passing it on to your partner:

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, stop having sex and visit your doctor or GUM clinic as soon as possible.

If you have been diagnosed with trichomoniasis, make sure that any sex toys you have used are cleaned. You should also avoid sharing them, to make sure the infection does not spread.

Content supplied by NHS Choices