Exogenous factors affecting the nails. Cosmetics, trauma, and occupational influences.

The external factors associated with nail disorders are multiple. Although not totally inclusive, this discussion has presented the more common cosmetic, traumatic, and industrial causes of nail disorders. Several common entities, such as the brown staining of fingernails in heavy tobacco smokers, have been omitted intentionally because little difficulty is encountered in determining their cause. Therefore, in evaluating a patient with abnormal nails, one should consider various external factors in addition to primary disease processes. Patch testing to determine if contact sensitivity is involved, in addition to a careful investigation of habits, employment, and exposures is mandatory.