There are several reasons for hair loss among which are thyroid gland disorders, heredity, hormones, excessive stress, chemotherapy, certain prescription drugs and dehydration.
Hair loss is the appearance of thinning hair or bald patches on the scalp, eyebrows, eyelashes, or on areas of the body that previously had hair, such as the arms or legs. On average, everyone naturally loses 50-100 of their 100,000 scalp hairs per day. Abnormal hair loss is caused when hair falls out at an accelerated rate, or when over time, hairs are not replaced as quickly as they fall out.
Hair loss can happen to men, women, infants and children in all socioeconomic strata and geographic areas. Genetic hair loss (androgenetic alopecia) is the most common type of hair loss. Also known as male pattern baldness or female pattern baldness, it affects around 80 million people in the United States, according to the American Academy of Dermatology.
Hair loss can gradually build over weeks or months, or it can occur abruptly, such as when it occurs with telogen effluvium (sudden hair loss due to a stressful physical event). Hair loss can also be due to other hair disorders, such as alopecia areata, an autoimmune disease in which the body attacks its own hair, or trichotillomania, a psychological disorder in which people pull out their own hair