The hair perforation test, also known as an in vitro hair perforation test, is a laboratory test used to help distinguish the isolates of dermatophytes, such as Trichophyton mentagrophytes and its variants.[1] The test is performed by placing an organism into a petri dish containing water, yeast extract, and hair. The Mayo Clinic's mycology laboratory has identified five common dermatophytes; Microsporum gypseum, Microsporum canis, Trichophyton rubrum, Trichophyton mentagrophytes, and Trichophyton tonsurans.[2]