There are many different causes of hair loss, all with different treatments. We will cover the more common causes below.
The most common cause of hair loss, or alopecia, is often referred to as male-patterned baldness. More appropriately, this condition is termed androgenic alopecia, and can affect women as well as men. Twenty-five percent of men aged 25 years have some degree of clinically apparent androgenic alopecia and over 40% of men will develop androgenic alopecia at some point in their life. Androgenic alopecia results from progressive shortening of the anagen cycle, the part of the hair cycle responsible for hair growth, with resultant decreased time for hair growth.
Hair loss usually begins with the frontoparietal scalp and then the vertex. Female-pattern baldness is similar but more diffuse, without complete baldness and maintaining the anterior hairline.
Fortunately hairs on the sides and back of the scalp are androgen-independent and thus do not suffer from androgenic alopecia - it is these hairs which are used for hair transplants and why hair transplants last.
Androgenic alopecia is genetically determined and its development is related to age and presence of hormones and the corresponding receptors.
The second most common form of alopecia is alopecia areata. This form of hair loss results in rapid loss of hair in circular or oval patches. It may be episodic or persistent. There is no definite reason why alopecia areata develops, but there is a genetic predisposition, and popular opinion favors an autoimmune disorder.
Alopecia areata only affects 0.1% of people. Approximately 3 months after surgery, childbirth, crash dieting, other stressful events, hair can enter an extended resting cycle referred to as telogen effluvium. Usually <50% of the scalp is affected and recovery is complete once the triggering event is resolved.
A wide range of medications can cause hair loss. The most widely known are chemotherapy drugs but other more common drugs, including blood thinners and Vitamin A, can cause hair loss. After taking the medications, hair growth is abruptly interrupted and growing hairs are shed after 1-4 weeks. This form of hair loss rapidly affects 80-90% of the scalp but complete recovery can be expected once the medication is stopped.
Certain infections can cause hair loss. Children may have hair loss caused by a fungal infection of the scalp. The infection is easily treated with antifungal medicines.
Hair loss may occur as part of an underlying disease, such as lupus or diabetes. Since hair loss may be an early sign of a disease, it is important to find the cause so that it can be treated.
Finally, tightly pulling hair can cause hair loss. People who wear pigtails or use tight hair rollers can pull the hair and cause traction alopecia. If the pulling is stopped before scarring of the scalp develops, the hair will grow back normally. However, scarring can cause permanent hair loss. Hot oil hair treatments or chemicals used in permanents may cause inflammation (swelling) of the hair follicle, which can result in scarring and hair loss.