Onychomycosis (yeast infection): Your nail thickened and yellowed, there was a small debris towards the nail tip. If left untreated, your entire nail will split, deform, or fall. Fungus only affects the nails if you are injured or if you have another skin disease. Toenails infection can also occur without injury. You can treat yourself or go to a doctor. The healing of the fingernails can take 6 months and the healing of the toenails can take 1 – 2 years.