The loss of hair in human beings is called alopecia. Bald patches typically develop on the head but can develop elsewhere on the body. The precise cause of these bald patches varies from case to case, but typically includes factors like aging, genetics, malnutrition, illnesses, and medications. Contrary to popular belief, baldness is not caused by dandruff, wearing hats too often, or poor blood circulation through the scalp, and different types of alopecia are each associated with a separate trigger. Bald patches may eventually grow back, or they might not, and it is the underlying cause of the baldness determines the longevity and severity of the bald spots.
Androgenic alopecia is the most common form of balding in humans and is sometimes referred to as androgenetic alopecia or alopecia androgenetica. Depending on the sex of the balding individual, this condition is more commonly known as male pattern baldness or female pattern baldness. Androgenic alopecia in males is marked by a receding hairline that begins at both temples and ends at the crown. Over time, bald patches develop on the top of the scalp. Female pattern baldness differs from that of males as it does not usually cause bald spots but an overall thinning of the hair on the scalp.
Androgenic alopecia has been linked to changes in age and hormones as well as a person's genetic makeup. It becomes more severe with age, and studies suggest that nearly 75 percent of men and 60 percent of women over the age of 80 experience hair loss in the mid-frontal region of the head.
Men with androgenic alopecia usually have hormone levels that are different from those of other men. Total testosterone levels are typically lower, but the level of free androgens, like dihydrotestosterone (DHT), is quite high. Most research indicates that male pattern baldness is, to some extent, X-linked, or linked to the transmission of the X chromosome as well as to other genes that do not appear to be sex-related. They conclude that men with fathers who suffered hair loss have a much higher risk of developing hair loss as well.
Another form of hair loss is alopecia areata, which causes sudden hair loss in a specific area. Due to its tendency to develop rapidly and cause baldness in one particular area, it is commonly called spot baldness. Very rarely, alopecia areata has been known to spread beyond its initial zone to the whole scalp or even the entire body. It is not contagious and is thought to be an autoimmune disorder in which the individual's immune system attacks hair follicle, leading to swelling and hair loss. Hair lost as a result of this condition usually returns after several months.
Toxic alopecia is marked by the disruption of growth in the anagen phase, which causes hair shafts to weaken and break. This condition can result from various causes, including severe illness or fever, high doses of vitamin A, chemotherapy, radiotherapy, and some diseases. Hair loss is usually temporary and stops once the body recovers.
Bald patches are also caused by scarring alopecia, which occurs when scars on the epidermis prevent hair from growing. Scars typically manifest after serious injuries such as a burn, but they can also be caused by diseases like tuberculosis, lupus, some skin infections, and skin cancer. Scarring usually permanently prevents hair from returning.