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|Classification and external resources|
Alopecia in a 33-year-old man.
Alopecia (pron.: //, from Classical Greek ἀλώπηξ, alōpēx, meaning "fox") means loss of hair from the head or body. Alopecia can mean baldness, a term generally reserved for pattern alopecia or androgenic alopecia. Compulsive pulling of hair (trichotillomania) can also induce hair loss. Hairstyling routines such as tight ponytails or braids may cause traction alopecia. Both hair relaxer solutions, and hot hair irons can also induce hair loss. In some cases, alopecia is due to underlying medical conditions, such as iron deficiency.
Generally, hair loss in patches signifies alopecia areata. Alopecia areata typically presents with sudden hair loss causing patches to appear on the scalp or other areas of the body. If left untreated, or if the disease does not respond to treatment, complete baldness can result in the affected area, which is referred to as alopecia totalis. When the entire body suffers from complete hair loss, it is referred to as alopecia universalis. It is similar to the effects that occur with chemotherapy.
Signs and symptoms 
Symptoms of alopecia include hair loss, skin lesions, and scarring. In male-pattern hair loss, loss and thinning begin at the temples and the crown and either thins out or falls out. Female-pattern hair loss occurs at the frontal and parietal.
The following section details many research aspects. Although the various pathways may (or may not) be clinically relevant, none of the current models trying to explain androgenetic alopecia is able to explain why hair-follicles transplanted from one site (often temporal scalp) to another continue to produce growing hair for many years or even lifelong. Another general limitation in understanding alopecia is the lack of studies comparing how many identical vs. non-identical twins of people with androgenetic alopecia also have hair-loss. Such studies are very powerful as they reveal just how much (or how little) of the hair-loss is really genetically determined.
Causes of alopecia include:
- Alopecia mucinosa
- Androgenic alopecia
- Chronic inflammation
- Dissecting cellulitis
- Fungal infections (such as tinea capitis)
- Hair treatments (chemicals in relaxers, hair straighteners)
- Hereditary disorders[which?]
- Hormonal changes
- Hyperthyroidism and hypothyroidism
- Hypervitaminosis A
- Iron deficiency or malnutrition in general
- Lupus erythematosus
- Medications (side effects from drugs, including chemotherapy, anabolic steroids, and birth control pills)
- Pseudopelade of Brocq
- Radiation therapy
- Scalp infection[which?]
- Secondary syphilis
- Telogen effluvium
- Traction alopecia
- Tufted folliculitis
Hair follicle growth occurs in cycles. Each cycle consists of a long growing phase (anagen), a short transitional phase (catagen) and a short resting phase (telogen). At the end of the resting phase, the hair falls out (exogen) and a new hair starts growing in the follicle beginning the cycle again.
Normally, about 40 (0-78 in men) hairs reach the end of their resting phase each day and fall out. When more than 100 hairs fall out per day, clinical hair loss (telogen effluvium) may occur. A disruption of the growing phase causes abnormal loss of anagen hairs (anagen effluvium).
Because they are not usually associated with an increased loss rate, male-pattern and female-pattern hair loss do not generally require testing. If hair loss occurs in a young man with no family history, drug use could be the cause.
- The pull test helps to evaluate diffuse scalp hair loss. Gentle traction is exerted on a group of hairs (about 40–60) on three different areas of the scalp. The number of extracted hairs is counted and examined under a microscope. Normally, fewer than three hairs per area should come out with each pull. If more than ten hairs are obtained, the pull test is considered positive.
- The pluck test is conducted by pulling hair out "by the roots". The root of the plucked hair is examined under a microscope to determine the phase of growth, and is used to diagnose a defect of telogen, anagen, or systemic disease. Telogen hairs have tiny bulbs without sheaths at their roots. Telogen effluvium shows an increased percentage of hairs upon examination. Anagen hairs have sheaths attached to their roots. Anagen effluvium shows a decrease in telogen-phase hairs and an increased number of broken hairs.
- Scalp biopsy is used when the diagnosis is unsure; a biopsy allows for differing between scarring and nonscarring forms. Hair samples are taken from areas of inflammation, usually around the border of the bald patch.
- Daily hair counts are normally done when the pull test is negative. It is done by counting the number of hairs lost. The hair from the first morning combing or during washing should be counted. The hair is collected in a clear plastic bag for 14 days. The strands are recorded. If the hair count is >100/day, it is considered abnormal except after shampooing, where hair counts will be up to 250 and be normal.
- Trichoscopy is a noninvasive method of examining hair and scalp. The test may be performed with the use of a handheld dermoscope or a video dermoscope. It allows differential diagnosis of hair loss in most cases.
- Minoxidil (Rogaine) is a nonprescription medication approved for androgenetic alopecia and alopecia areata. In a liquid or foam, it is rubbed into the scalp twice a day. This is the most effective method to treat male-pattern and female-pattern hair loss. However, only 30–40% of patients experience hair growth. Minoxidil is not effective for other causes of hair loss. Hair regrowth can take eight to 12 months. Treatment is continued indefinitely because, if the treatment is stopped, hair loss resumes again. Most frequent side effects are mild scalp irritation, allergic contact dermatitis, and increased facial hair.
- Finasteride (Propecia) is used in male-pattern hair loss in a pill form taken on a daily basis. It is not indicated for women and is not recommended in pregnant women. Treatment is effective within six to eight months of treatment. Side effects include decreased libido, erectile dysfunction, ejaculatory dysfunction, gynecomastia, and myopathy. Treatment should be continued as long as positive results occur. Once treatment is stopped, hair loss resumes again.
- Egg oil, in Indian, Japanese, Unani (Roghan Baiza Murgh) and Chinese traditional medicine, was traditionally used as a treatment for alopecia.
- AminoMar C (Viviscal): This is a marine complex, which allegedly nourishes the hair follicle from within. Using supplements with AminoMar C for 4–6 mo were claimed, in a small study (with a control group of five), funded by the manufacturer, to encourage normal healthy hair growth, making hair stronger and more vibrant.
- Corticosteroids injections of into the scalp can be used to treat alopecia areata. This type of treatment is repeated on a monthly basis. Physician may prescribe oral pills for extensive hair loss due to alopecia areata. Results may take up to a month to be seen.
- Dithranol (anthralin, Dritho-Scalp) is available as a cream or ointment, applied to the scalp and washed off daily. More commonly, it is used to treat psoriasis. Results may take up to 12 weeks to be seen.
- Hormonal modulators (oral contraceptives or antiandrogens such as spironolactone and flutamide) can be used for female-pattern hair loss associated with hyperandrogenemia.
- Surgical options, such as follicle transplants, scalp flaps, and alopecia reduction, are available. These procedures are generally chosen by those who are self-conscious about their hair loss, but they are expensive and painful, with a risk of infection and scarring. Once surgery has occurred, six to eight months are needed before the quality of new hair can be assessed.
- In hair transplants, a dermatologist or cosmetic surgeon takes tiny plugs of skin, each which contains a few hairs, and implants the plugs into bald sections. The plugs are generally taken from the back or sides of the scalp. Several transplant sessions may be necessary.
- Scalp reduction is the process is the decreasing of the area of bald skin on the head. In time, the skin on the head becomes flexible and stretched enough that some of it can be surgically removed. After the hairless scalp is removed, the space is closed with hair-covered scalp. Scalp reduction is generally done in combination with hair transplantation to provide a natural-looking hairline, especially those with extensive hair loss.
- Wigs are an alternative to medical and surgical treatment; some patients wear a wig or hairpiece. They can be used permanently or temporarily to cover the hair loss. High-quality, natural-looking wigs and hairpieces are available.
In May 2009, researchers in Japan identified a gene, SOX21, that appears to be responsible for hair loss in humans and a researcher in India found a link between androgenic hormone and hair loss. Androgenic alopecia is a counterproductive outcome of the anabolic effect of androgens.
In March 2012, George Cotsarelis discovered a causal link between elevated levels of prostagladin D2 (PDG2) and androgenic alopecia. Abnormally high levels of PDG2 (a nearly three-fold increase) were discovered in tissue samples of balding areas compared to haired areas of the scalp. During the course of the research, a PDG2-binding receptor, GPR44, was also discovered. Compounds aimed at targeting the GPR44 receptor are currently being researched.
See also 
- Alopecia in animals
- Androgenic alopecia – male pattern baldness
- Lichen planopilaris
- Management of baldness
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