How long does toenail fungus last ?

Life long: Usually onychomycosis persists life long unless treated with an effective anti-fungal agent such as terbinafine or itraconazole which have replaced the more toxic griseofulvin.

Fungi spread by: Spores, which are everywhere. They don't wash out in the laundry or are killed in the drier. While it's entirely possible to clear up a toenail fungus with proper treatment, people who are susceptible to fungal infections tend to get re-infected, no differently than people who are prone to strep throats that keep getting them. Without treatment, the fungus never really goes away.