FPHL or androgenetic alopecia is the most common cause of hair loss in women and one of the most common chronic problems seen by dermatologists worldwide (Varothai and Bergfeld, 2014). FPHL is a nonscarring form of alopecia in which the frontal hairline is maintained, but there is progressive hair thinning at the vertex of the scalp. Thinning of the hair is secondary to alteration of the hair cycle with shortening of the anagen phase and simultaneous lengthening of telogen. This increase in the resting phase and decrease in the growth phase of the hair cycle results in the miniaturization of hair because long terminal hairs are gradually replaced by short vellus hairs (Messenger and Sinclair, 2006, Sinclair et al., 2011).
Another cause of eyebrow hair loss is genetic predisposition. Many patients naturally have thinner eyebrows that run in their family. This is one of the biggest reasons patients seek our services. Medical conditions such as hypothyroidism, eczema, and alopecia areata (spot baldness) can also lead to brow hair falling out. It’s important to determine the cause of your condition to find an effective treatment.
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]