Dermatophytic onychomycosis: Ringworm of the nail, the most common fungus infection of the nails (onychomycosis). Onychomycosis makes the nails look white and opaque, thickened, and brittle. Older women and men and women with diabetes or disease of the small blood vessels (peripheral vascular disease) are at increased risk. Artificial nails (acrylic or "wraps") increase the risk because when an artificial nail is applied, the nail surface is usually abraded with an emery board damaging it, emery boards can carry infection, and water can collect under the nail creating a moist, warm environment for fungal growth. Alternative names include tinea unguium.