Hair loss, also known as alopecia or baldness, refers to a loss of hair from part of the head or body.^[2] Typically at least the head is involved.^[4] The severity of hair loss can vary from a small area to the entire body.^[7] Inflammation or scarring is not usually present.^[4] Hair loss in some people causes psychological distress.^[3]

Common types include male- or female-pattern hair loss, alopecia areata, and a thinning of hair known as telogen effluvium.^[4] The cause of male-pattern hair loss is a combination of genetics and male hormones; the cause of female pattern hair loss is unclear; the cause of alopecia areata is autoimmune; and the cause of telogen effluvium is typically a physically or psychologically stressful event.^[4] Telogen effluvium is very common following pregnancy.^[4]

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