The field of dermatology includes diseases of both skin and the skin appendages, namely hair, sweat glands, and nails. A great variety of conditions affect the skin appendages, and some are isolated to the hair, nail, or sweat glands, whereas some are found in the setting of a more widespread cutaneous or systemic disease.
Diseases of the hair include alopecia, hirsutism, and those affecting the hair color and hair shaft. Evaluation of these conditions includes a directed history along with evaluation of the scalp, eyebrows, eyelashes, and body hair. Beyond a biopsy of the affected region to assess the hair follicles, bedside tests such as the pull test and tug test help investigate the integrity of the hair follicles and shafts, respectively.
Examination of the nail units includes inspection of the nail plate, nail folds, and cuticles, as well as the nail bed and lunula. Like hair conditions, some nail conditions are isolated to the nail, such as melanonychia, and others are associated with more widespread disease. Some nail findings can be a clue to an underlying skin condition, such as the pitting seen in psoriasis, whereas other nail findings can be associated with systemic diseases such as half-and-half nails with proximal white discoloration that can be seen in patients with kidney disease. Still other nail conditions can be secondary to medications or trauma.
Lastly, sweat glands include the widespread eccrine glands and more localized apocrine variant predominantly found in the axillae and groin. This portion of the atlas will provide images of those conditions involving the skin appendages, including the hair, sweat glands, and nails.