Trichomoniasis is a sexually transmitted infection (STI) that a person can pass on through vaginal, oral, or anal sex. It can cause a foul smelling discharge and itching, but many people have no symptoms.

A parasite called Trichomonas vaginalis causes trichomoniasis, or trich, which is highly curable if a person seeks treatment. However, only about 30% of people with trich experience symptoms, according to the Centers for Disease Control and Prevention (CDC).

Without treatment, trich can lead to complications. It can affect a pregnancy, and it also appears to increase the risk of getting and passing on HIV.

Trichomoniasis is one of the most common sexually transmitted infections (STIs) in the United States, where the CDC estimate that it affects close to 3.7 million people. It is the most common curable STI.

close up of a woman's legs on the toilet who may be uncomfortable if she has trichomoniasisShare on Pinterest
A person with trichomoniasis may experience discomfort when urinating.
Credit: Getty images.

T. vaginalis, the parasite that causes trich, can pass from one person to another during sex. A person can transmit it during oral, anal, or vaginal sex or through genital touching.

In females, trich is most likely to affect the lower genital tract. In males, it affects the urethra, the tube through which urine passes.

Other parts of the body, such as the anus, hands, or mouth, cannot usually become infected.

The following people have a higher chance of getting trich:

  • females
  • people with more than one sexual partner
  • those with a history of trich or other STIs
  • people who have unprotected sex

As the number of sexual partners that a person has increases, so does their risk of getting trich.

Symptoms may appear between 5 and 28 days after exposure, or they may appear later or not at all.

When symptoms are present, they can affect males and females differently.

Minor symptoms include irritation, but someone with a more severe case may have inflammation with discharge.

Possible symptoms in females include:

  • frothy, foul-smelling vaginal discharge, which may be clear, white, gray, yellow, or green
  • vaginal discharge with blood
  • genital irritation
  • discomfort during sex or when urinating
  • swelling in the groin
  • frequent urination
  • in rare cases, lower abdominal pain

Symptoms in males may include:

  • discharge from the urethra or penis
  • itching in the penis
  • burning sensations after ejaculating or urinating
  • frequent need to urinate
  • pain when urinating

Trichomoniasis can lead to several complications, including those below.

Problems during pregnancy

Experts have linked trichomoniasis with complications during pregnancy, including:

  • preterm birth
  • early rupture of the membrane
  • low birth weight in newborns
  • infertility

A woman can sometimes pass on the infection to the newborn during delivery, but this is rare.

It is safe to receive treatment with metronidazole during pregnancy.

Other problems

Trich may increase the risk of reproductive tract infections.

At least one study suggests that there may also be a link between trich and human papillomavirus (HPV), the virus that causes cervical cancer. More research is necessary, however, to clarify the association.

HIV risk

A trich infection can increase the risk of getting HIV and other STIs, especially in females.

Scientists believe that this increased risk could be due to:

  • inflammation
  • a reduced immune response
  • changes in the balance of vaginal flora, in females

These factors may lower a person’s natural protection from the virus.

To diagnose a trichomoniasis infection, a doctor will:

  • carry out a pelvic exam
  • take a sample of vaginal or penile discharge for examination under a microscope
  • take a vaginal swab for a culture test in a laboratory

The results of a lab test will come back in about a week.

Preparing for the appointment

Women should aim to schedule the appointment for a time when they are unlikely to be menstruating.

Before the appointment, they should avoid using deodorant on the vulva, as this masks odor and can cause irritation. The doctor may also advise them to avoid vaginal intercourse or inserting any object, including tampons, into the vagina for 24–48 hours beforehand

A Pap (smear) test does not check for trich. If a person has a clear Pap test, they may still have trich or another STI.

As trich increases the risk of passing on HIV, people with HIV should also have a trich test at least once a year.

If the result is positive

If the test results are positive, a doctor will prescribe treatment and discuss what to do next.

The person will need to:

  • inform all of their sex partners, as they will also need a test
  • take the whole dose or course of treatment to stop the infection from coming back
  • avoid sexual contact until the treatment is complete
  • seek further advice if symptoms remain a few days after finishing a course of antibiotics

The doctor may also recommend having tests for other STIs.

Trich is easy to treat in males and females, including during pregnancy.

Treatment usually involves taking a single dose of an antibiotic by mouth. A doctor may also prescribe a vaginal suppository or a cream to apply topically.

Antibiotic medications that kill parasites include metronidazole (Flagyl) and tinidazole (Tindamax).

People should not consume alcohol while taking metronidazole, as there may be an adverse reaction, which can lead to abdominal cramps, nausea, headaches, and flushing.

If symptoms continue after taking the treatment, a person should go back to see their doctor again.

Breastfeeding after treatment

People should not take tinidazole while breastfeeding.

Metronidazole is safe to use, but a doctor may suggest waiting 12–24 hours after taking it before breastfeeding.

To prevent infection or reinfection, any sexual partners should also receive treatment.

Ways of preventing the risk of infection or reinfection include:

  • limiting the number of sexual partners
  • avoiding sex for 7–10 days after treatment for trich
  • not using a douche, as this can affect the healthy bacteria in the vagina
  • limiting or avoiding the use of recreational drugs and alcohol, as these increase the risk of unsafe sex
  • using a condom for protection during sex

A condom can prevent transmission to some extent, but it is not fully reliable because the parasite can pass from person to person on areas of the body that it does not cover.

Anyone who has symptoms or thinks that they have been exposed to trich should speak to a doctor.

Trichomoniasis is a sexually transmitted infection. It spreads easily and can lead to complications, but effective treatment is available.

Treatment can prevent complications and stop trich from spreading to another person.