There are numerous potential etiologic factors in alopecia. Endocrine abnormalities, genetic factors, systemic illness, drugs, psychological abnormalities, diet, trauma, infections, and structural hair defects may all cause hair loss. Evaluation of the patient must be thorough and include history, physical examination, and appropriate laboratory work-up.

History is of utmost importance in focusing on the correct diagnosis (Table 1). The duration of hair loss, family history, location of hair loss (diffuse vs. focal), drug intake history, hair care habits (bleaching, back brushing, permanent waving), and presence of coincidental acne and abnormal menstrual cycles are all important clues in determining the correct diagnosis. It is important to determine whether the hair falls out from the roots or breaks off along the shaft since there are separate dintinct differential diagnoses for each of these problems (Table 2).

Clinical examination of all hair-bearing areas should be performed. Checking for inflammation, infection and scarring (loss of the hair follicle) is of utmost importance. The differential diagnosis of hair loss is based on whether the hair loss is scarred or not (Table 3).

Regarding laboratory testing, nonscarring alopecia may require a complete blood count, thyroid-stimulating hormone, serum ferritin, and VDRL. In women with androgenetic alopecia and other virilizing signs, an androgen work-up for free testosterone, androstenedione, and dehydroepiandrosterone (DHEAS) is advised. Scarring alopecias are difficult to differentiate from one another clinically and almost always require a 4-mm scalp biopsy for determination of the correct diagnosis.