1

The nails have several functions that can be severely impaired by nail diseases. Fingernails are necessary for manipulating objects and for tactile sensation, but they are also an important communication tool. Patients with severe fingernail abnormalities may have great problems in social life and often try to hide their hands from sight. Toenails contribute to foot biomechanics: patients with thickened toenails often complain of problems with wearing shoes and of pain when walking. Although aggressive treatment for diseases limited to the nails should be avoided (apart from the few exceptions that require strong therapies), the psychologic impact that nail diseases may have should always be kept in mind.

2

Nails are anatomically different from the skin: the nail plate is a cornified dead structure that only reflects a disease localized elsewhere, in the nail matrix or nail bed. Recognizing the localization of the disease is mandatory to know which portion of the nail apparatus should be reached by treatment (Box 1).

3

Topical treatments are not as successful on the nails as on the skin because the nail plate prevents drug penetration, and the nail matrix is deeply located under the proximal nail fold.

4

The nail grows slowly; mean fingernail growth rate is 3 mm/mo, and mean toenail growth rate is 1 mm/mo. It may take a long time (6 months for fingernails and 18 months for toenails) before appreciable nail improvement is seen after treatment. This time should be clearly explained to patients to avoid frustration and treatment withdrawal.