Brittle splitting nails (onychoschizia) is a condition characterized by weak or thin fingernails or toenails that easily split and break.  It mostly affects women and may occur if nails are either dry and brittle from too little moisture, or soft and brittle from too much moisture.

Repeated wetting and drying of nails is the chief cause of brittle splitting nails. Factors that may worsen the condition include use of harsh chemicals, such as nail polish remover or detergents, sun exposure, low humidity, and dry, cold weather. In rare cases, the condition may be due to a vitamin deficiency or internal disease.