Androstenedione, which is mostly produced in the ovary and adrenal glands, is converted to testosterone by 17β-hydroxysteroid dehydrogenase. Testosterone then circulates throughout the body to reach its target tissues. Androgen-metabolizing enzymes have been found in many parts of the hair follicle (Table 1; Bolognia et al., 2012). The presence of those enzymes makes the pilosebaceous unit a site of androgen metabolism and synthesis (Fazekas and Sandor, 1973). Circulating free testosterone either binds to intracellular androgen receptors in the hair bulb and dermal papilla, which facilitates miniaturization of the follicle, or is metabolized into dihydrotestosterone (DHT) by the enzyme 5-alpha-reductase. DHT then binds the same receptor but with much greater affinity (Kaufman, 2002, Levy and Emer, 2013). Of the androgens depicted in Figure 1, only DHT and testosterone bind to androgen receptors (Burger, 2002).
Telogen effluvium is a condition where a large number of hair follicles enter the resting phase known as telogen. As these hairs may fall off, it is not replaced with new hair at the same area and this leads to a bald patch on the eyebrows. A number of hormonal factors (like with hypothyroidism and pregnancy) may be responsible and it is also related to certain diseases, nutritional deficiencies, chronic medication use and even metal toxicity. It is now also known that stress can push many more hair follicles than normal into this phase.
Hair loss may also occur due to dieting. Franchised diet programs which are designed or administered under the direction of a physician with prescribed meals, dietary supplements and vitamin ingestion have become popular. Sometimes the client is told that vitamins are a necessary part of the program to prevent hair loss associated with dieting. From a dermatologists’s standpoint, however, the vitamins cannot prevent hair loss associated with rapid, significant weight loss. Furthermore, many of these supplements are high in vitamin A which can magnify the hair loss.
An unhealthy gut is also a common source of inflammation and that alone can contribute to hair loss. But lack of robust digestion and a healthy gut bacterial environment will not only lead to nutrient deficiencies that impact hair health but an imbalanced impacting all other hormones related to hair loss such as low thyroid, poor estrogen metabolism and elevated cortisol.
The most common type of hair loss seen in women is androgenetic alopecia, also known as female pattern alopecia or baldness. This is seen as hair thinning predominantly over the top and sides of the head. It affects approximately one-third of all susceptible women, but is most commonly seen after menopause, although it may begin as early as puberty. Normal hair fall is approximately 100-125 hairs per day. Fortunately, these hairs are replaced. True hair loss occurs when lost hairs are not regrown or when the daily hair shed exceeds 125 hairs. Genetically, hair loss can come from either parents side of the family.
Hair loss may also occur due to dieting. Franchised diet programs which are designed or administered under the direction of a physician with prescribed meals, dietary supplements and vitamin ingestion have become popular. Sometimes the client is told that vitamins are a necessary part of the program to prevent hair loss associated with dieting. From a dermatologists’s standpoint, however, the vitamins cannot prevent hair loss associated with rapid, significant weight loss. Furthermore, many of these supplements are high in vitamin A which can magnify the hair loss.
Reduce stress. When you are stressed, your body starts shutting down processes that aren’t necessary for survival. This shutdown can occur with physical stressors, like surgery or an illness, and emotional stress, which often manifests as physical symptoms. Loss may occur up to three months after the stressful event and may take another three to grow again.[24]
Scalp hair loss may be a common complaint among men and women, but in my practice, loss of eyebrow hair is a major concern among my female patients. Because eyebrows frame the face, hair loss in this area can dramatically change one's appearance, and since eyebrow hair loss is not easily concealed, it can be, for some women, an even more devastating loss than scalp hair loss.
Thyroid hormone receptors were detected in both dermal and epithelial compartments of the human pilosebaceous unit.[48] T4 and T3 decrease the apoptosis of hair follicles and T4 prolongs the duration of anagen in vitro.[49] Thyroidectomy delays initiation of anagen. Administration of thyroxine advances anagen, initiation of which is however delayed once toxic doses are given. Therefore, ratio of telogen to anagen hairs is increased in hypothyroidism as well as hyperthyroidism.[50] Thus, the hair follicles are affected in thyroid disorders, and madarosis is caused due to disturbances in hair cell kinetics. Hypothyroidism is associated with generalized hair loss probably due to coarse, dull, and brittle hair with reduced diameter.[51] The eyebrows and eyelashes may also be lost. Loss of lateral one-third of eyebrows known as Hertoghe sign[38] is a characteristic sign of hypothyroidism.[52] Some people also refer to it as Queen Anne's sign,[53] after Anne of Denmark whose portrait with shortened eyebrows has been interpreted by some as indicative of the presence of goiter, even though such a fact has not been proved by any known sources of information. Madarosis may even be the presenting sign in hyperthyroidism.[21] In hyperthyroidism, there is thinning with breaking off and shortening of hair.[54] Madarosis can also occur in hypopituitarism, hypoparathyroidism,[21] and hyperparathyroidism.[55]
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