The hair growth cycle consists of three phases: Anagen, Catagen, and Telogen.
⦁ Anagen (the growth phase) lasts between 3 and 10 years. During this phase, rapid cell division occurs in the hair bulb and dermal papilla. Hair matrix in this phase is extremely sensitive to drugs, growth factors, hormones, stress, immunologic and physical injury.
⦁ Catagen (transitional phase) lasts 2 to 3 weeks, whereby programmed cell death occurs.
⦁ Telogen (resting phase) lasts 3 to 4 months, during which hairs are shed from the scalp.
Hair loss is typically related to one (or more) of the following factors:
⦁ Family history (heredity). The most common cause of hair loss is due to genetic flaws which become more prominent as a person gradually gets older. This condition is called androgenic alopecia, which occurs in both males and females (illustrated in the pictures below).
⦁ Hormonal changes and medical conditions. A variety of conditions can cause permanent or temporary hair loss, including hormonal changes in pregnancy, childbirth and menopause. Medical conditions include alopecia areata or scarring alopecia due to infections.
⦁ Medications and supplements. Hair loss can be a side effect of certain drugs, such as those used for cancer, arthritis, depression, heart problems, gout and high blood pressure.
⦁ Radiation therapy to the head. The hair may not grow back the same as it was before.
⦁ A very stressful event. Many people experience hair thinning several months after a physical or emotional shock. Known as telogen effluvium, this type of hair loss is usually temporary.
⦁ Hairstyles and treatments. Excessive hairstyling or hairstyles that pull your hair tight (e.g. high ponytails) can cause a type of hair loss called traction alopecia. Certain chemical treatments can also lead to hair loss due to scalp inflammation. Permanent loss may occur.