Although not completely understood, hair loss can have many causes: Pattern hair loss Male pattern hair loss is believed to be due to a combination of genetics and the male hormone dihydrotestosterone. The cause in female pattern hair loss remains unclear. Infection * Dissecting cellulitis of the scalp * Fungal infections (such as tinea capitis) * Folliculitis from various causes * Demodex folliculitis, caused by Demodex folliculorum, a microscopic mite that feeds on the sebum produced by the sebaceous glands, denies hair essential nutrients and can cause thinning. Demodex folliculorum is not present on every scalp and is more likely to live in an excessively oily scalp environment. * Secondary syphilis Drugs * Temporary or permanent hair loss can be caused by several medications, including those for blood pressure problems, diabetes, heart disease and cholesterol. Any that affect the body's hormone balance can have a pronounced effect: these include the contraceptive pill, hormone replacement therapy, steroids and acne medications. * Some treatments used to cure mycotic infections can cause massive hair loss. * Medications (side effects from drugs, including chemotherapy, anabolic steroids, and birth control pills) Trauma * Traction<unk>  is most commonly found in people with ponytails or cornrows who pull on their hair with excessive force. In addition, rigorous brushing and heat styling, rough scalp massage can damage the cuticle, the hard outer casing of the hair. This causes individual strands to become weak and break off, reducing overall hair volume. * Frictional<unk>  is hair loss caused by rubbing of the hair or follicles, most infamously around the ankles of men from socks, where even if socks are no longer worn, the hair often will not grow back. * Trichotillomania is the loss of hair caused by compulsive pulling and bending of the hairs. Onset of this disorder tends to begin around the onset of puberty and usually continues through adulthood. Due to the constant extraction of the hair roots, permanent hair loss can occur. * Traumas such as childbirth, major surgery, poisoning, and severe stress may cause a hair loss condition known as telogen effluvium, in which a large number of hairs enter the resting phase at the same time, causing shedding and subsequent thinning. The condition also presents as a side effect of chemotherapy – while targeting dividing cancer cells, this treatment also affects hair's growth phase with the result that almost 90% of hairs fall out soon after chemotherapy starts. * Radiation to the scalp, as when radiotherapy is applied to the head for the treatment of certain cancers there, can cause baldness of the irradiated areas. Pregnancy Hair loss often follows childbirth in the postpartum period without causing baldness. In this situation, the hair is actually thicker during pregnancy owing to increased circulating oestrogens. Approximately three months after giving birth (typically between 2 and 5 months), oestrogen levels drop and hair loss occurs, often particularly noticeably around the hairline and temple area. Hair typically grows back normally and treatment is not indicated. A similar situation occurs in women taking the fertility-stimulating drug clomiphene. Other causes * Autoimmune disease.<unk><unk>  is an autoimmune disorder also known as "spot baldness" that can result in hair loss ranging from just one location<unk><unk>  monolocularis) to every hair on the entire body<unk><unk>  universalis). Although thought to be caused by hair follicles becoming dormant, what triggers<unk><unk>  is not known. In most cases the condition corrects itself, but it can also spread to the entire scalp<unk>  totalis) or to the entire body<unk>  universalis). * Skin diseases and cancer. Localized or diffuse hair loss may also occur in cicatricial<unk>  (lupus erythematosus, lichen plano pilaris, folliculitis decalvans, central centrifugal cicatricial<unk> , postmenopausal frontal fibrosing<unk> , etc.). Tumours and skin outgrowths also induce localized baldness (sebaceous nevus, basal cell carcinoma, squamous cell carcinoma). * Hypothyroidism (an under-active thyroid) and the side effects of its related medications can cause hair loss, typically frontal, which is particularly associated with thinning of the outer third of the eyebrows (also seen with syphilis). Hyperthyroidism (an over-active thyroid) can also cause hair loss, which is parietal rather than frontal. * Sebaceous cysts. Temporary loss of hair can occur in areas where sebaceous cysts are present for considerable duration (normally one to several weeks). * Congenital triangular<unk>  – It is a triangular, or oval in some cases, shaped patch of hair loss in the temple area of the scalp that occurs mostly in young children. The affected area mainly contains vellus hair follicles or no hair follicles at all, but it does not expand. Its causes are unknown, and although it is a permanent condition, it does not have any other effect on the affected individuals. * Hair growth conditions. Gradual thinning of hair with age is a natural condition known as involutional<unk> . This is caused by an increasing number of hair follicles switching from the growth, or anagen, phase into a resting phase, or telogen phase, so that remaining hairs become shorter and fewer in number. An unhealthy scalp environment can play a significant role in hair thinning by contributing to miniaturization or causing damage. * Obesity. Obesity-induced stress, such as that induced by a high-fat diet (HFD), targets hair follicle stem cells (HFSCs) to accelerate hair thinning in mice. It is likely that similar molecular mechanism play a role in human hair loss. Other causes of hair loss include: *<unk>  mucinosa * Biotinidase deficiency * Chronic inflammation * Diabetes * Pseudopelade of Brocq * Telogen effluvium * Tufted folliculitis Genetics Genetic forms of localized autosomal recessive hypotrichosis include: Type OMIM Gene Locus LAH1 DSG4 18q12 LAH2 LIPH 3q27 LAH3 P2RY5 13q14.12-q14.2
symptom of Alopecia areata
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