Onychomycosis - Complications of fungal nail infections
NHS Choices Medical Reference
In most cases, fungal nail infections will not cause any further complications. However, if the infection is left untreated, it may cause pain and discomfort.
In toenails, this can eventually lead to difficulty wearing shoes and walking. In fingernails, this could cause difficulty writing.
If the infection spreads to the skin around the nail, it can result in cellulitis (bacterial infection under the skin) or osteomyelitis (infection of the bone). These complications more commonly occur among older people and people with health conditions such as diabetes.