Griseofulvin is a spirobenzofuran produced by a number of Penicillium species, first isolated in the 1930s by Raistrick's group. Griseofulvin is a selective antifungal agent used to treat skin infections in animals and humans. Griseofulvin acts by binding to fungal tubulin and inhibiting the mitotic spindle. Griseofulvin's ability to bind to keratin is considered an important aspect of the metabolite's access to dermatophytic fungi. More recently, griseofulvin has become an important phenotypic marker in Penicillium taxonomy.