Disease may affect the nail fold, nail plate or nail bed (see SKIN – Nail). Inflammation of the nail fold is called paronychia: acute paronychia is usually caused by a minor injury allowing in bacteria; chronic paronychia is often an occupational hazard, due to constant exposure of the hands to water – for example, in the catering industry, agriculture and housework – but may also be caused by impaired circulation in the fingers. Often, ANTIBIOTICS are sufficient for treatment, but sometimes surgical incision under local anaesthetic is needed (called wedge resection of the nail).

PSORIASIS, eczema (see DERMATITIS) and fungal infection (see FUNGAL AND YEAST INFECTIONS) are common causes of disease of the nail plate and result in gross thickening of toenails. Deformity of the nail may also point to systemic disease, as in CLUBBING, or the spoon-shaped concave nails (koilonychia) of severe iron deficiency. Acute illnesses may temporarily disturb nail growth causing horizontal ridges (Beau's lines) which grow out slowly.

Onycholysis is separation of the nail plate from its bed. It may be due to psoriasis of the nail bed and trauma, or may occur spontaneously.