Trichomoniasis is a sexually transmitted disease (STD) caused by a parasite that is passed from one person to another through sexual contact or through contact with damp objects that contain the parasite. Also known as “trich” or “trick,” it does not pose a major health risk, but can be uncomfortable for those who are infected.

Trichomoniasis infects 7.4 million women and men every year, according to the U.S. Centers for Disease Control and Prevention (CDC). The illness is relatively rare in men and more common in women. In fact, trichomoniasis is the most common, curable STD in young women and affects about 5 to 10 percent of all women, according to the National Women’s Health Resource Center. In addition, some studies have found that up to 50 percent of women infected with other STDs are also infected with trichomoniasis.

A single-celled protozoan parasite called Trichomonas vaginalis causes trichomoniasis. This parasite has a tail resembling a whip that it uses to propel itself through vaginal and urethral mucus. The vagina is the most common site of infection in women, while the urethra is the most common site of infection in men. The parasite that causes trichomoniasis cannot survive in the mouth or rectum.

Women can develop trichomoniasis after sexual contact with infected men or women – e.g., through penis-to-vagina or vulva-to-vulva contact. Infection can also be spread through oral or possibly anal sex. In addition, a woman can become infected if her genitals come into contact with certain objects that contain the parasite. These objects include toilet seats, damp towels or washcloths and wet clothing, such as swimsuits.

Infection is most commonly transmitted during vaginal intercourse. Men usually contract the infection from sexual contact with an infected woman.

Trichomoniasis is considered one of the three main causes of vaginitis. However, many women with trichomoniasis do not experience the symptoms of vaginitis (e.g., burning sensation, discomfort during urination). However, even if no symptoms are present, people with trichomoniasis can still pass the disease on to others.

A trichomoniasis infection makes a person more vulnerable to other STDs, including the human immunodeficiency virus (HIV), which can cause acquired immune deficiency syndrome (AIDS). A trichomoniasis infection stimulates the immune system, resulting in higher production of the immune system response cells that the HIV virus targets. In addition, women who have both HIV and trichomoniasis are more likely to infect their partners with HIV.

Prolonged infection in women also can cause changes in cervical surface tissues. Complications of trichomoniasis in men include prostatitis (inflammation of the prostate) or epididymitis (inflammation of the tubes that carry and store sperm).