Reproductive hormone changes can also play a part, and dermatologists believe the same factors that cause hair loss from the scalp, a common problem for women as they age, may contribute to thinning brows. Nanette Santoro, M.D., ob/gyn and professor of reproductive endocrinology at the University of Colorado at Denver, says, “Abrupt hormone changes can cause sudden hair loss (telogen effluvium) that recovers over about six months' time. It happens postpartum to many women and can happen at menopause.”
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).
Toxic alopecia occurs when there is a disruption of hair growth in the anagen phase. This usually occurs following chemotherapy and radiotherapy.[94] Radiotherapy for various types of ocular tumors, eyelid and choroidal tumors have been reported to produce madarosis.[95–97] Hair loss due to radiation is usually reversible, but may be permanent when the dose of radiation is in the range of 50 to 60 Gy.[94]
Certainly when those testosterone levels rise, DHT is even more of a problem. DHT levels can be elevated and be within what doctors consider "normal range" on a blood test, but they may be high enough to cause a problem. The levels may not rise at all and still be a problem if you have the kind of body chemistry that is overly sensitive to even regular levels of chemicals, including hormones.
There is also a different in the form of 5AR enzyme (5 alpha reductase) found on the facial hair follicles vs. the scalp hair follicles. This enzyme converts testosterone into that more problematic DHT. Type I DHT is found in sebaceous glands on the face and genital area whereas Type II is found in hair follicles of the scalp. Type II DHT is typically more of a problem in men, but Type II is increased in disorders with high testosterone like PCOS.
There are numerous diseases that can affect the hair and scalp. Hair loss can be caused by a variety of conditions. Diseases such as alopecia areata, anemia, male/female pattern baldness, and infections of the scalp can all cause significant difficulty and loss of daily well-being. Stanford Dermatology has established a special clinic focusing on the diagnosis and treatment of these disorders of the hair.
A new entity variously called as trichodysplasia spinulosa,[128] trichodysplasia of immunosuppression,[129] and cyclosporine-induced folliculodystrophy[130] has been described in immunocompromised patients, usually organ transplant recipients on immunosuppression. It involves the development of alopecia predominantly of the face with indurated spinous papules. There is a profound loss of eyebrows[131] and sometimes eyelashes. The histopathologic picture is that of abnormal follicles with hyperkeratotic infundibula and absence of normal hair shafts. The inner root sheath epithelium showed proliferation in the cells and dystrophic trichohyaline granules. Electron microscopy of skin showed presence of intracellular viral particles.[132] This entity has lately been reported in immunosuppressive states in patients without organ transplantation such as leukemias and lymphoma.[133–136] van der Meijden et al. described the discovery of a new polyoma virus in a patient with trichodysplasia spinulosa.[131] Histopathological examination can reveal the diagnosis. A recent simple pull-test wherein the spicules can be plucked and examined under the microscope for inner root sheath keratinization has been described.[136] Some successful treatments described are cessation of cyclosporine therapy[130] and oral valganciclovir[137,138] and topical cidofovir.[131]
Eyebrows protect the eyes from sweat that trickles down the forehead. They also protect the bony ridges above the eyes. In addition to the above, the eyebrows play a very important function in facial expression and body language. Eyelashes protect the eyeball from small foreign bodies and irritants and stimulate the closing reflex. Both eyebrows and eyelashes play a very important cosmetic function, and thus contribute greatly to the self esteem of an individual.[9]
There can be any number of different factors contributing to your hair loss. If you’re reading this and thinking, “well I have that and that, and am going through that,” then you may already have an idea of what is a contributing cause for you. You may already be doing much of what is suggested here and may learn of additional ideas to consider trying.
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Dozens of other causes of eyebrow loss are also possible including a variety of infectious, autoimmune and inflammatory conditions. Consultation with a dermatologist or hair transplant surgeon is recommended. I strongly advise consulting a dermatologist before proceeding to hair transplantation for women over 40 with new onset eyebrow hair loss after age 40. 

Menopause is a natural biological process that all women experience at some point in their lives. During this time, the body goes through numerous physical changes as it adjusts to fluctuating hormone levels. Many women have unpleasant symptoms during menopause, including hot flashes, mood swings, and insomnia. Hair loss is another common occurrence.
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]
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.
Additionally, two other considerations are important for a patient who receives treatment for FPHL. First, there is a set of reasonable expectations in patients. Maintaining the current hair density can be considered a successful treatment because women tend to have further thinning as they age (Harfmann and Bechtel, 2015). Second, it is important to ensure that patients understand that progress is slow, and months or years can be required to see a significant improvement (Boersma et al., 2014, Yeon et al., 2011). In our practice, we wait at least 6 months to assess treatment efficacy.
Take extra care in looking after your hair. Use a gentle, nourishing shampoo (we love Bumble and Bumble Gentle Shampoo) to promote good condition and prevent breakage. Try using a silk or satin pillowcase. Avoid harsh styling products and techniques that apply heat to the hair (blow drying, curling irons etc) as these can cause more damage to fragile hair.
There’s no doubt that estrogen and hair loss are connected, but there are certain factors that determine how much of an effect estrogen levels have on your hair. As one of the main visible measures of your health, hair growth is often one of the first areas affected when hormones are off-balance. Let’s take a look at the links between estrogen hormonal imbalance and hair loss.