cycle: anagen (active growth), catagen (regression), and telo­gen (rest). Approximately 85–90% of hair follicles are in the anagen phase, while 10–15% are in the telogen phase, and less than 1% in the catagen phase. There are approximately 100,000 hair follicles on the scalp, and, on average, 50–100 hairs are normally lost every day [1]. Hair loss becomes a clinical problem when there are localized patches of hair loss or when the number of hairs lost daily exceeds the normal amount. Progressive thinning and excessive shedding of the scalp hair are the two most common hair complaints reported [2].

ring (or cicatricial) and non-scarring (or non-cicatricial) alo­pecias (Fig.21.1). When assessing a patient with alopecia, it is important to consider the chief complaint as stated by the patient, the chronicity, the age at onset, whether there is a pattern to the areas of hair loss, and if there have been any major stressors, physical or emotional, in the patient’s life. Androgenetic alopecia, also referred to as female or male pattern hair loss, is the most common type of hair loss due to hormonal effects at the level of the follicle and is what most patients refer to as “balding.” Generalized thinning is most commonly seen in alopecia areata, in which the etiology is autoimmune, or telogen effluvium, in which some physiologic stressor initiates abnormal shedding [2]. Other causes of hair loss include autoimmune conditions, underlying systemic problems like thyroid disease and iron deficiency, infections of the scalp, inflammatory processes, and habitual practices. Regardless of the underlying cause, both physical and psy­chological stress can exacerbate any form of hair loss.