Cututtuka na naman gwari galibi suna tasowa daga rashin daidaituwa mai sauƙi na ƙananan ƙwayoyin halitta a zahiri a cikin jiki.

Haƙiƙa an mallake ta da tarin fungi da ƙwayoyin cuta iri -iri, mafi yawan lokuta marasa lahani kuma har ma suna da mahimmanci don ingantaccen aikin jiki.

Koyaya, yana iya faruwa cewa wasu daga cikin waɗannan fungi suna yaduwa kuma suna zama masu cutarwa, ko kuma naman gwari na “waje”, wanda dabba ya watsa misali, yana haifar da kamuwa da cuta. Jimlar nau'ikan fungi 200-400 na iya haifar da cuta a cikin mutane⁵.

Koyaya, fungi da ke cikin muhalli na iya gurbata ɗan adam, misali:

• ta hanyar allurar rigakafi, yayin rauni misali (wanda ke haifar da sporotrichosis ko chromomycosis, da sauransu);
• ta hanyar inhalation na kyallen takarda (histoplasmosis, apergillosis, da sauransu);
• ta hanyar saduwa da mai cutar (candidiasis, ringworms, da sauransu);
• ta hanyar saduwa da dabba mai cutar.