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This is a common human parasite and occurs throughout the world. It is rather like T. vaginalis in appearance although it is slightly smaller (5–16 μm long, 2–15 μm wide), has a somewhat shorter undulating membrane, and the hydrogenosomes are arranged differently. Molecular studies indicate a close similarity between the two species and T. tenax may be a variant of T. vaginalis (Kucknoor et al. 2009). Trichomonas tenax is usually restricted to the oral cavity where it feeds on bacteria and tissue debris.

Trichomonas tenax does not form cysts and cannot survive passage through the digestive tract. Consequently, transmission probably involves contamination via kissing and the sharing of food and eating/drinking utensils. It is less host fastidious than T. vaginalis, and in addition to humans, it infects various domestic animals, including cats and dogs (Kellerová and Tachezy 2017). There is therefore the potential for zoonotic transmission between those besotted owners who inexplicably kiss their pets and those who do not follow basic hygiene during food preparation and consumption.

Although T. tenax is associated with periodontal diseases (Marty et al. 2017), it is also common in people with good dental hygiene. This is probably because strains of T. tenax differ in their pathogenicity (Benabdelkader et al. 2019). There are occasional reports of bronchopulmonary infections, but these are usually associated with pre‐existing pulmonary conditions, such as cancer.