Nail brittleness is a common complaint characterized by weak inelastic nails that split, flake and crumble. It may be a consequence of factors that alter nail plate production and/or factors that damage the already keratinised nail plate. It is often idiopathic. It can also be caused by many dermatological and systemic diseases, nutritional deficiencies, drugs and traumas. Environmental and occupational factors that produce progressive dehydration of the nail plate have an important role in nail brittleness. Treatment of brittle nails is often difficult. Preventative measures, together with oral supplementation of vitamins (especially biotin), oligo-elements and amino acids, can be useful in improving nail strength. Cosmetic treatment affords camouflage and a degree of protection.