Brittle nail syndrome is characterized by roughness of the surface of the nail plate, fragility or raggedness of the distal nail, and splitting and peeling. Brittle nails affect 20% of the population and are diagnosed most frequently in elderly individuals. Women are affected twice as frequently as men. The pathogenesis of brittle nail syndrome is not well understood, but it is thought to be due to an abnormality of keratin, keratin-associated proteins, water, and/or lipid content.

Clinical features of brittle nail syndrome are onychoschizia (horizontal splits within the nail plate), onychorrhexis (increased longitudinal ridging, or splitting), and onycholysis (detachment of the nail plate from its bed). While some patients present to the physician due to cosmesis, many complain of pain with a negative impact on daily activities.

It is usually idiopathic, but there are some dermatological and systemic diseases that can be associated with secondary brittle nail syndrome. Dermatologic conditions include Darier disease, pityriasis rubra pilaris, lichen planus, and alopecia areata. Systemic diseases include hypopituitarism, hypothyroidism and hyperthyroidism, diabetes mellitus, malnutrition, Raynaud disease, and polycythemia vera.