Mysophobia, also known as verminophobia, germophobia, germaphobia, bacillophobia and bacteriophobia, is a pathological fear of contamination and germs. The term was coined by William A. Hammond in 1879 when describing a case of obsessive–compulsive disorder (OCD) exhibited in repeatedly washing one's hands. Mysophobia has long been related to compulsive hand washing. Names pertaining directly to the abnormal fear of dirt and filth include molysmophobia or molysomophobia, rhypophobia, and rupophobia, whereas the terms bacillophobia and bacteriophobia specifically refer to the fear of bacteria and microbes in general.

The term "mysophobia" comes from the Greek μύσος ("musos"), "uncleanness" and φόβος ("phobos"), "fear".