Mechanism of AGA occurrence and diagnosis in women Androgenetic alopecia is hair loss caused by androgens in men or women with genetic susceptibility, usually starting between the ages of 12-40 years, with a slightly lower incidence in women than in men. The mechanism of AGA is that on sensitive hair follicles, dihydrotestosterone binds to androgen receptors and activates downstream target genes, which gradually transforms the original larger terminal hair follicles into miniaturized hair follicles, resulting in the conversion of terminal hairs into fine hairs, which manifest as thinning and eventual loss of hair in the lesioned area. The pathology is characterized by a shortening of the follicular growth phase in the early stages and an increase in the proportion of resting hair follicles; in the later stages, the follicles become smaller and the terminal hairs are replaced by fine hairs, and finally the fine hair follicles disappear. Clinically, female AGA is not the same as male, female patients have more scattered distribution of fine hair, although the forehead and the top of the scalp is the most significant, but generally will not be completely lost, and the forehead hairline generally does not move back, but in the forehead to retain a circle of complete hairline. Female AGA condition is often classified into three levels according to Ludwig’s method. Most female AGA patients have normal menstruation, are able to have normal pregnancies, and have normal sex hormone tests. Therefore, unless the patient has signs and symptoms of hyperandrogenism such as hirsutism, severe folliculitis or masculine features, a full hormone test is usually not necessary. If necessary, androgen excess can be determined by measuring serum levels of total or free testosterone, dehydroepiandrosterone sulfate and prolactin. AGA in women needs to be differentiated from other causes of diffuse hair loss, such as postpartum, anemia, endocrine changes or other systemic disorders. Measurement of serum thyroxine, iron and ferritin levels can help distinguish between these causes of alopecia areata. Treatment options for AGA in women (1) Minoxidil: Originally a drug for hypertension, it was later found to promote hair follicle growth and was used to treat hair loss. The mechanism of minoxidil in the treatment of hair loss is not fully understood, and it is thought that it may be related to opening potassium channels, reducing intracellular calcium ion concentration, stimulating the differentiation and proliferation of hair follicle epithelial cells, prolonging the anagen phase, and also dilating blood vessels and reducing lymphocyte infiltration around the hair follicle. Dermatology is mainly used for the treatment of AGA (both men and women) and heavy baldness. It is mainly used topically, and two concentrations of 2% and 5% (Mandy) are available. Men mostly use 5% concentration, women can choose 2%, must be used directly on the dry scalp, the initial period can be used once a day in the morning and evening, later on the effect and stability can be gradually reduced to once a night and maintain. Before use, it is advisable to gently massage the scalp until it is hot to increase absorption. Generally, it is effective for 4-6 months, but after 1 month of discontinuation, hair loss can be resumed, so continuous treatment is needed. There are generally no significant side effects, but individual patients may experience facial hirsutism, eye and face and ankle swelling. It should not be used for pregnant women. (2) Cyproterone acetate: It is an androgen receptor competition inhibitor, which exerts anti-androgenic effects by competing with androgen receptors. CPA is used for the treatment of acne, seborrhea, hirsutism and female-type AGA caused by hyperandrogenemia in women. Take 1 capsule per day for 21 days and then stop taking it for 1 week and then take it as described above. Improvement is usually expected after 6-8 months. Adverse reactions include loss of libido, depression, weight gain, headache and stomach discomfort in rare cases, and chloasma and liver function impairment in long-term users. Pregnancy, lactation and a history of vascular embolism should not be used. (3) Spironolactone: Similar in structure to aldosterone, it is an aldosterone competition inhibitor, originally used for the treatment of edematous diseases, hypertension and primary aldosteronism, etc. Because it can inhibit testicular and adrenal microsomal cytochrome p450 enzymes, thus inhibiting gonadal production of androgens, and can compete in the skin to block DHT receptors, exerting anti-androgenic effects. It is mainly used in dermatology for the treatment of AGA, acne vulgaris and hirsutism in women. Generally 60-100mg/d orally in 2-3 doses, which can be increased to 150-200mg/d after 1-3 months. 6 months is a course of treatment. Adverse effects are mainly menstrual disorders and electrolyte disorders. Renal insufficiency and pregnant women are prohibited. (4) Cimetidine: It is an H2 receptor orange antagonist, which can block the binding of DHT and hair follicle receptors to exert anti-androgenic effects, and has significant hair growth effects on some women with AGA, as well as improving the development of acne, seborrhea and hirsutism. The recommended use is 300mg, 5 times/day for 5 months; or in decreasing doses, i.e. 600mg 3 times a day for 10 days and then 400mg 3 times a day for 4 weeks and 200mg 3 times a day for 3 months. This drug is a second-line drug for the treatment of AGA in women and should be used depending on the treatment. It is contraindicated in pregnant and lactating women. In addition, this drug may have transient WBC decrease, ALT increase, facial flushing, light diarrhea, etc., but usually can return to normal after stopping the drug. (5) Vitamin A acid: Vitamin A acid can affect cell membrane fluidity and lipid composition, regulate hair follicle and epidermal cell differentiation, and promote hair follicle growth. However, the clinical effect alone is not good, but mostly used in combination with minoxidil and other local, in order to increase the absorption of the latter and improve the efficacy, but because there are contraindications, it is appropriate to separate external rubbing, should not be used at the same time. In addition, 5α-reductase inhibitors, including finasteride (trade name Bofax), dutasteride, etc., are generally not suitable for use in female patients because they have only weak clinical effects but more adverse effects on female patients.