Trichomoniasis is a sexually transmitted infection that is caused by a parasite. It can be passed on through vaginal, oral, or anal sex.

Trichomoniasis, or trich, is highly curable, but it does not cause symptoms in everyone who gets it. Without treatment, it can lead to complications.

It is one of the most common sexually transmitted infections (STIs) in the United States (U.S.). Around 3.7 million people in the U.S. are thought to have it, but only 30 percent have symptoms.

Having a trich infection seems to increase the risk of getting and passing on HIV.

Fast facts about trichomoniasis

  • Trichomoniasis is a sexually transmitted infection (STI) often referred to as “trich.”
  • In women, it affects the vulva, vagina, and urethra.
  • To prevent reinfection, patients and their sexual partners must complete treatment.
  • Trich often leads to vaginitis, or inflammation of the vagina.
  • Only 30 percent of people with trichomoniasis develop symptoms.
  • Trichomoniasis during pregnancy increases the risk of premature labor.

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Trichomoniasis symptoms can be uncomfortable, but often there are no symptoms.

Trichomoniasis, or “trich,” is a sexually transmitted infection (STI) caused by a microscopic, single-cell protozoan parasite called Trichomonas vaginalis. The parasite is passed on during sexual intercourse.

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

Other parts of the body such as the anus, hands, or mouth, cannot normally contract the infection.

According to the Centers for Disease Control and Prevention (CDC), trichomoniasis is the most common curable sexually transmitted disease (STD).

The parasite is passed from partner to partner during sex.

The following people have a higher chance of getting trich:

  • Women, and especially older women
  • People with more than one sexual partner
  • Those with a history of trich or other STIs
  • People who have unprotected sex

It can be passed on during oral, anal, or vaginal sex, and also through genital touching.

The risk increases with the number of sexual partners a person has.

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

Up to 70 percent of people, and especially men, have no symptoms when they have trich.

When symptoms are present, they can affect men and women differently.

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

Symptoms for women include:

  • frothy, foul-smelling vaginal discharge, which may be clear, white, gray, yellow, or green
  • vaginal discharge with blood
  • genital irritation
  • burning sensations around the genitals or when urinating
  • swelling in the groin
  • painful intercourse, known as dyspareunia
  • needing to urinate frequently
  • painful urination, or dysuria

Symptoms for men include:

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

A number of complications are linked to trich.

HIV risk

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

This could be because of:

  • inflammation
  • a reduced immune response
  • a change in balance in vaginal flora

Problems during pregnancy

Trichomoniasis is linked to a number of complications during pregnancy.

These include:

  • preterm birth
  • early rupture of the membrane
  • low birth weight, of less than 5.5 pounds
  • passing on the infection to the newborn during delivery

Fortunately, trich can be treated safely with antibiotics during pregnancy.

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
  • send a sample to the lab for a test

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

To prepare for the appointment, a woman should :

  • avoid douching for at least 24 hours beforehand, as this washes away discharge
  • avoid using deodorant on the vulva, as this masks smells and can cause irritation
  • avoid vaginal intercourse or inserting any object, including tampons, into the vagina for 24–48 hours beforehand
  • schedule an appointment when it is unlikely to be on her period

A Pap, or smear, test does not check for trich. If you have a clear Pap test, you may still have trich or another STI.

A person who tests positive for trich should be tested for other STIs, too.

As trich increases the risk of passing on HIV, women with HIV should also have a trich test once a year or more.

Trich is easy to treat in men and women, including those who are pregnant.

It usually involves a single dose of either metronidazole (Flagyl) or tinidazole (Tindamax). These are antibiotic medications that kill parasites. These come in pill form and are taken by mouth.

If symptoms continue after taking the treatment, you should go back to see your doctor again.

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

Ways of preventing the risk of infection or reinfection include:

  • not having sex with multiple partners
  • avoiding sex for 7 to 10 days after treatment for trich
  • not using a douche, as this can affect the healthy bacteria in the vagina
  • not abusing drugs and alcohol, as these increase the risk of unsafe sex
  • using condoms—correctly—during sex

A condom can prevent transmission in the parts it covers, but the parasite can be passed on in areas that are not covered, so a condom is not fully reliable.

Anyone who has symptoms or who thinks they have been exposed to trich should speak to their health care provider.