Just because your nails look bad, doesn't always mean your nails are infected with fungus. Ugly and distorted nails can be caused by fungus but are often the result of long term and repeated trauma. Many athletes such as ballet dancers, ice skaters, runners, and soccer players are highly prone to developing dystrophic, yellowing nails. Usually a podiatrist can tell on visual inspection and history if the nails are fungal, however, if uncertain the nails will be sent to a lab to be tested.