Hair Foundation
Hair Loss and Its Causes

April 14, 2008
James L. Breeling

Androgenetic Alopecia

Non-scarring Alopecia

Scarring Alopecia

Androgenetic Alopecia

We think of having hair as normal and losing hair as abnormal. We would rather keep our hair than lose it. However, the principal cause of hair loss in men is not abnormal in the sense of being a bizarre phenomenon. It is better described as a normal phenomenon that causes hair loss ranging from virtual undetectability to balding over most of the scalp. This cause of hair loss is androgenetic alopecia, also called male-pattern hair loss. A variant form is called female-pattern hair loss. It involves some causative factors that are the same and some that may be different from those associated with male-pattern hair loss.

The incidence of androgenetic alopecia has not been extensively studied in all populations. Its incidence in the most-studied population of Caucasians may be near 100% when the study includes minor shifts of hair growth from mature hair to vellus ("peach fuzz") hair with advancing age. Androgenetic alopecia that is apparent enough to be characterized as a "type" occurs in 50% or more of both men and women.

The Classic Types of Hair Loss Due to Androgenetic Alopecia

Types of male- and female-pattern hair loss graded by severity are illustrated in charts. These charts are standardized guides for assessing the progression of androgenetic alopecia. While the charts are used as standard guides, they are not universally applicable; some variant patterns of hair loss do not fall clearly into any "type", but may show characteristics of two or more of the charted types.

Standard Classification of Male-Pattern Hair Loss Due to Androgenetic Alopecia

Male-pattern hair loss does not necessarily have a linear progression associated with age-that is, balding that begins as Type I at age 20 does not necessarily progress to Type VIII at age 45. Rather, androgenetic alopecia may progress slowly or rapidly and may or may not progress to a more severe stage. The pattern of progression may be somewhat predictable by patterns of hair loss in the individual's family; familial pattern is not completely reliable for predicting the eventual loss of hair.

Standard Classification of Female-Pattern Hair Loss Due to Androgenetic Alopecia

Female-pattern hair loss is more diffuse than that seen in males. It has the appearance of thinning hair over much of the scalp rather than total hair loss in a defined area of balding. In addition to the standard Ludwig classification, a "Christmas tree" pattern of diffuse hair loss was identified by dermatology specialist Elise Olsen, MD. In this pattern, the broader base of the Christmas tree shape is at the front of the scalp, the narrower top of the Christmas tree shape in the middle of the scalp.

The peak period of onset for female-pattern hair loss tends to occur later in life than in males; onset in the 40-50 age range is not uncommon. As in males, early onset tends to be associated with more severe eventual hair loss. In both males and females, hair follicles at the back of the scalp are not affected by the genetically-driven processes of androgenetic alopecia. The protected follicles at the back of the scalp provide the reservoir for use in hair transplantation or other surgical means of hair restoration.

What Causes Androgenetic Alopecia?

The causes of androgenetic alopecia are (1) genetic predisposition, and (2) androgenic metabolism under genetic control. Although the roles of genes and androgenic hormones are known in general, the complete story of the cause of androgenic alopecia is not yet known (see Genes, Hair Growth and Hair Loss). Androgenetic alopecia is believed to be polygenic-that is, a number of different genes are involved; not all of the genes have been identified. The role of androgenic hormones in androgenetic alopecia is better characterized:

Androgens and Androgenetic Alopecia

The androgens are a large class of steroid hormones, some of which are also called anabolic because they undergo anabolism-conversion into other components of the body's biochemistry. The androgenic (masculinizing) effects of the androgens are those associated with maturation of sex characteristics as a male grows and develops, including deepened voice and growth of facial, pubic and underarm hair. The anabolic effects are associated with protein assembly and increase of mass in muscle and bone. Anabolic effects of androgens are the effects sought by athletes who "dope" with androgens to increase muscle mass.

By their androgenic and anabolic effects, androgens influence growth, development and function of many organs and tissues-e.g., reproductive organs, liver, kidneys, red blood cells, immune system, central nervous system, skin and hair follicles. Testosterone is a "master androgen", one of the most important synthesized by the body. It is a male hormone produced in the testicles. Women produce very little testosterone, but other androgens produced in ovaries and adrenal glands can be converted to testosterone and testosterone metabolites such as 5-alpha-dihydrotesterone (DHT) by enzymatic action. Testosterone can be converted to the potent female hormone estradiol by action of the enzyme aromatase.

Testosterone does not exert its effects directly on target tissue such as the cells in hair follicles. While testosterone can bind to the androgen receptor on a target cell, specific enzymes convert testosterone to a more potent metabolite that has specific effect on cell function. The enzyme 5-alpha-reductase converts testosterone into the more potent dihydrotestosterone (DHT), which has a greater affinity than testosterone for binding with the androgen receptor. Two types of the enzyme 5-alpha-reductase are known; Type 2 is the form that converts testosterone to DHT in hair follicle tissue. It also converts testosterone to DHT in prostate tissue, causing proliferation of prostate tissue and enlargement of the prostate in men. Drugs such as finasteride (see Non-surgical Hair Loss Treatments) that inhibit the enzymatic action of 5-alpha-reductase reduce the level of DHT in hair follicle and prostate tissue, halting or reversing hair loss and shrinking prostate tissue.

A genetic predisposition causes hair follicle cells to process DHT in an aberrant fashion, resulting in inhibition of cellular function and alteration of the hair growth cycle (see Hair Science: How and Why Hair Grows). The hair cycle is shortened in genetically predisposed hair follicles. Shortening of the growth cycle results in hair that is cycled too rapidly; eventually, the follicle stops producing mature hair altogether. The relationship between DHT and hair loss is confirmed by studies showing that men who are congenitally deficient in 5-alpha-reductase (and thus deficient in DHT) do not develop androgenetic alopecia.

A battery of other enzymes converts testosterone into many other forms that influence growth and development throughout the body.

Treatment of Androgenetic Alopecia

A number of successful treatments for androgenetic alopecia have been developed (see Advancements in Treating Hair Loss).

Some individuals benefit from a medical treatment of hair loss approved by the U.S. Food and Drug Administration (see Proven Medical Treatments for Hair Loss).

Surgical hair restoration has an excellent record of success (see Surgical Hair Restoration).

Hair restoration is a lucrative market for so-called miracle cures. See "Miracle Cures" for Hair Loss) Purveyors of miracle cures rely upon continued belief in myths and folk tales regarding hair loss and hair restoration (see Myths, Folk Tales & Scams About Hair Loss).

Other Causes of Hair Loss

Androgenetic alopecia is the most common cause of hair loss in adults, but many other causes of hair loss have been identified. While each of these other causes can be described separately, a useful scheme is to organize them into two broad categories:

  • Non-scarring causes, in which hair is lost temporarily or permanently but the scalp is left intact, and
  • Scarring causes, in which the condition that causes hair loss also causes injury and scarring of the scalp.
  • Because injury and subsequent scarring can destroy hair follicles, scarring alopecia is more likely to result in permanent hair loss. While it is easy to recognize when hair is being lost, it can be difficult to discover the cause. Some hair loss is a manifestation of an underlying disease. Some hair loss is due to skin conditions that are recognizable only by a medical specialist. Unexplained hair loss always warrants medical consultation.

    Non-Scarring Alopecia

    Alopecia Areata

    Alopecia areata is a major cause of hair loss that isn't due to androgenetic alopecia. Its cause is unknown; autoimmunity or other immune system dysfunction is suspected (see Genes, Hair Growth and Hair Loss: What We Know and Don't Know).

    Hair loss of alopecia areata ranges from patchy to total scalp balding and even to hair loss over the entire body. The onset of alopecia areata can be rapid-literally overnight in some instances. Alopecia areata should be treated by a physician with knowledge and experience in treating hair and scalp disorders. Treatment should be individualized to the patient and tailored to the severity of the disease. Patients with extensive hair loss may consider a temporary or permanent wig.

    Telogen Effluvium

    Telogen effluvium is an abnormality of hair cycling in which hairs in anagen (growth) phase are rapidly shifted to telogen (resting) phase, and subsequently shed. Hair loss due to telogen effluvium is typically discovered when extraordinary hair shedding is noted in comb, brush, hat or on a pillow.

    A great variety of causes are known for telogen effluvium. If the cause can be identified and removed, telogen effluvium may resolve over a period of weeks to months. If a cause cannot be discovered and removed, the abnormal hair cycling and hair shedding can become chronic.

    Known causes of telogen effluvium include:

  • Hormonal-hypothyroidism, postpregnancy hormonal changes, pre- or post-menopausal hormonal changes.
  • Physical illness-anemia, systemic disease involving major organs, major surgery.
  • Nutritional-deficiency of some or all of calories, protein, essential fatty acids, vitamins, minerals (deficiency may sometimes be caused by nutrient-deficient diets, sometimes by inability to absorb or metabolize nutrients).
  • Drugs-many prescribed and over-the-counter drugs have been implicated; sometimes it is difficult to distinguish the effect of a drug from the effect of a condition for which it is taken.
  • Severe acute or chronic psychological stress-may be involved in physical illness in a primary or secondary role.
  • Anagen Effluvium

    A condition is which hair in the anagen (growth) phase of the hair cycle is shed, often by breaking off at the level of the scalp. A frequent cause is exposure to a toxic agent (such as chemotherapy drugs, colchicine, mercury, thallium), ionizing radiation (cancer therapy or accidental exposure), and severe protein restriction in a protein-deficient diet. Some toxic agents-notably thallium-can be fatal with a single dose because they cannot be removed from tissue before they cause death. Anagen effluvium usually resolves after removal of the toxic agent or addition of sufficient protein to the diet. The classic condition due to protein-calorie malnutrition is kwashiorkor, recognized especially in children with protruding abdomens and tangled, broken hair.

    Loose Anagen Syndrome

    The name "loose anagen syndrome" has been given to a condition in which hair in the anagen (growth) phase is easily pulled from hair follicles by combing, brushing or simply by running the fingers through the hair. The incidence of loose anagen syndrome appears to be highest in fair-haired people, especially in fair-haired children. The condition is familial and thus probably genetic in origin. Symptoms may slowly improve with advancing age. In some patients, loose anagen syndrome is accompanied by features of other familial conditions that cause hair to be wooly and uncombable.

    Hereditary/Congenital Hair Abnormalities

    Hair loss and hair shaft abnormalities of hereditary or congenital cause usually become apparent in infancy or early childhood. Conditions range from total hair loss in infancy to hair shaft abnormalities such as hair breakage, misshapen hair shafts such as "bamboo hair" and "twisted" hair, wooly hair and uncombable hair. Congenital hair abnormalities may be associated with underlying congenital disorders that require the attention of a pediatric specialist.

    Triangular Alopecia

    As implied by its name, triangular alopecia is the loss of hair in a triangle-shaped patch, usually above the temple. The condition may be congenital and often appears in childhood. Hair loss is usually permanent.

    Hair Loss as a Symptom of Underlying Disease

    Hair loss can be a symptom-even an initial symptom-of underlying disease involving the endocrine system (pituitary, thyroid, adrenal glands), digestive system (intestines, liver), urinary tract (kidneys) or skin. Unexplained hair loss should be pursued by medical examination.

    Cancer of the Scalp

    Persistent scalp lesions with or without hair loss can be an indication of a primary skin cancer or a metastasis from another site. A persistent scalp lesion should be examined by a physician.


    This "hair plucking mania" is a condition in which hair loss is caused by the individual's obsessive/compulsive plucking of his/her own hair. In a mild form, the plucking may be a routine, semi-automatic behavior while the individual reads, watches, television, etc. In more severe obsessive/compulsive form, the plucking is consciously carried out, perhaps in front of a mirror.

    The individual is likely to deny the behavior, even when evidence of plucked patches is clear. The consciously compulsive hair plucker will usually conceal plucking instruments and discard plucked hairs to avoid discovery. In contrast, piles of plucked hairs may be discovered around the semi-automatic plucker's favorite chair.

    Trichotillomania is a condition requiring psychological evaluation and treatment.

    Scarring Alopecia

    Injury to the scalp can be caused by physical trauma and disease. Injury can result in destruction of hair follicles and scarring of the scalp, with permanent hair loss.

    Physical, Chemical, Thermal and Radiation Injury

    Physical Injury: Laceration

  • Automobile accident
  • Workplace accident
  • Criminal assault
  • Physical Injury: Traction

    Corn-rowing and tight braiding can exert enough pressure on skin and hair follicles to cause injury and scalp scarring, with permanent hair loss.

    Chemical Injury

  • Hair-straightening chemicals, especially in "home-made" solutions, are capable of causing chemical injury to the scalp and destruction of hair follicles with scalp scarring. Chemicals that can soften the strong fibers of the hair shaft are potent enough to injure scalp skin.
  • Hair bleaches can injure scalp skin, especially with recurrent use.
  • Permanent waving solutions may cause scalp injury, especially with frequent recurrent use.
  • Thermal (Heat) Injury

  • Accidental injury-house fire, automobile crash with fire, explosion with fire.
  • Permanent waving with excessive heat.
  • Radiation Injury

    Exposure to ionizing radiation above the level regarded as safe can cause tissue destruction and scarring.

    Central Centrifugal Scarring Alopecia

    This is a broad classification of scarring alopecias that have some features in common.

    Follicular Degeneration Syndrome

    A condition that has high incidence in people of African ancestry, its defining feature is degeneration and death of hair follicles on the scalp. While the cause is unknown, suspected causes or contributing factors are excessive use of (1) hot-comb hair straightening, and (2) chemical hair straightening.

    Folliculitis Decalvans

    Areas of scalp inflammation also exhibit boggy patches with boil-like pustules and scabby crusts. Moist areas may be infected with skin bacteria, but whether the infection is cause or effect is not known. Immune system dysfunction is also suspected as a cause.


    Pseudopelade is a condition of unknown cause that slowly progresses from small patches of hair loss to large areas of permanent hair loss and scalp scarring. Lesions are not markedly inflamed. The incidence of the condition is higher in women than in men. Pseudopelade is frequently discovered when a small patch of hair loss is noted while combing, brushing or styling hair. The cause is unknown.

    Folliculitis Keloidalis Nuchae

    Inflamed hair follicles progress to acne-like lesions and eventual formation of the lumpy scars called keloids. Incidence is higher in people of African ancestry, who also have a genetic predisposition to form keloidal scars after injury. The lesions of folliculitis keloidalis nuchae occur frequently on the back of the neck just below the hairline, but also can involve the scalp. Cause of the condition is unknown.

    Autoimmune Diseases

    A number of diseases of known or suspected autoimmune origin can cause scarring alopecia. These include cutaneous sarcoidosis, lupus erythematosus, lichen planus and lichen planopilaris (see Diseases and Disorders of the Scalp). Cutaneous sarcoidosis is known as the "great imitator" because its appearance can be so similar to that of other conditions. Sarcoidosis is a systemic disease that can affect every organ system, including skin. Cutaneous sarcoidosis (sarcoidosis of the skin) occurs in about a third of patients with systemic sarcoidosis. Clinical features includescaly scalp skin, tender red nodules just under the skin's surface, lumpy papules and decolorized patches on the skin. On visual inspection alone, it is difficult to differentiate cutaneous sarcoidosis from other skin diseases such as lichen planus and lupus erythematosus. A full diagnostic workup including skin biopsy may be necessary to confirm a diagnosis. The cause of sarcoidosis is unknown, but an autoimmune origin is suspected.


    Bacterial, viral and fungal scalp infections that are severe or prolonged may cause scalp injury, scalp scarring and hair loss. (see Diseases and Disorders of the Scalp).


    Skin cancer that invades deep layers of the skin can destroy hair follicles and cause scalp scarring.

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