Excessive hair loss (alopecia) is defined as losing enough hair that a person has visibly thin or balding patches. A number of events or circumstances can interrupt the normal cycle of hair growth and cause hair loss to occur (e.g., heredity, hormones, medication). Hair loss may be temporary or permanent, depending on the cause. Excessive hair loss caused by heredity is by far the most common cause in both men and women, so much so that it is often considered normal instead of a medical condition.

Hair loss is generally classified as either scarring or nonscarring. Nonscarring refers to hair loss such as male pattern hair loss, where the scalp is not damaged but hair is lost. Scarring hair loss occurs at scarred or damaged areas of the scalp and is much less common than nonscarring hair loss. It is usually caused by trauma (e.g., burns, physical injury) but may be caused by disease as well (e.g., skin cancer, lupus).

Hair loss is usually noticeable by simply looking into a mirror. An unusually high number of hairs discovered on a pillow or hairbrush are also common indicators that abnormal hair loss may be occurring. There is no cure for hereditary hair loss. However, treatments are available that may grow hair or slow the progression of hair loss, with medications and surgery being the most widely used (e.g., minoxidil, hair transplantation).  

Often, the ability to prevent or stop hair loss largely depends on the underlying cause. Loss of hair due to a stressful event or disease (telogen effluvium) does not usually persist once the underlying cause has ended or been removed. Non-hereditary hair loss is far less common but often much more easily preventable. It may be possible to prevent further hereditary hair loss or to regrow hair in some patients if it is treated early, though current treatments do not work for everyone.

Excessive hair loss caused by heredity is by far the most common form of hair loss. Anecdotal evidence has long suggested that patterned hair loss in men (androgenetic alopecia) is inherited as a dominant trait from the maternal side of the family. However, the genetic predisposition for patterned hair loss in both men and women is likely attributed to a combination of multiple genes, the influence of androgens (male sex hormones) and age.

Hair loss does not pose any health risks in and of itself, although it may rarely indicate an underlying medical condition or disease (e.g., lupus). Problems or difficulties experienced due to hair loss are often psychological, but can affect a person’s quality of life.

More commonly, hair loss may cause individuals to become introverted, have low self-esteem or feel tense or unattractive.  This is particularly true in men or women who begin to lose hair in their teenage years or early 20s (premature male or female pattern baldness), because these feelings tend to be more troubling in younger patients. Although treatment for hair loss is not necessary, patients who are emotionally impacted by the condition may benefit from seeking treatment.

A typical hair shaft has three layers:

• Cuticle. The outermost layer and the main hair structure.
  
  
• Cortex. Middle layer that gives strength to the hair shaft. The cortex also determines the color and texture of the hair.
  
  
• Medulla. The innermost or core of the hair. The body and strength of the hair are determined within the medulla.

Hair is composed of a protein called keratin and is produced in hair follicles (tiny, tubular structures through which hair grows) located in the outer layer of the skin (epidermis). Each person is born with a set number of follicles. The follicle holds the lower part of the hair shaft in place and contains blood vessels that cause new hair to grow. The growth of hair from these follicles is cyclical and happens in three stages:

• Growth (anagen) phase. May last two to three years for any given hair. On a normal scalp, about 80 to 90 percent of hair follicles are in the growth phase at any given time.
  
  
• Involutional (catagen) phase. Reduction in size of the hair. Approximately 1 to 3 percent of hair on the scalp is undergoing involution at any given moment. The involutional phase is a transitional period the hair undergoes before being shed. Typically, it lasts about two or three weeks.
  
  
• Resting (telogen) phase. Shedding of hair from the scalp. Following involution, hairs go through a resting phase for about two to three months. At the end of this time, the hairs are shed and the growth cycle (anagen) is reinitiated. On a normal scalp, approximately 5 to 10 percent of hairs on the scalp are in the resting phase at any given time, with about 75 hairs shed every day.

The hair growth cycle varies from one person to another. A full head of hair has about 100,000 hairs, with the exception of redheads, who have fewer hairs, and blondes, who have more. Up to 30 percent of hair may be lost by middle age as a normal part of the aging process. Male pattern hair loss, for example, is not typically noticeable until at least half of the hairs in a designated area have fallen out. The condition also causes remaining hairs to thin, making the appearance of hair loss more defined.

Hair loss becomes abnormal when it is being shed faster than it can be regrown, when it is thinner than before or when hair comes out in patches (alopecia areata). Abnormal hair loss may happen to anyone, though its frequency may vary according to race. Women experience hair loss nearly as frequently as men do. However, they tend to lose less hair due to hormonal differences and different balding patterns. Women may also be able to disguise their hair loss more effectively than men through differences in hair length and styling.

Hair loss (alopecia) is generally classified as either scarring or nonscarring. The most common types of nonscarring hair loss include:

• Androgenetic alopecia. By far the most common form of hair loss. Caused by heredity, it occurs in women almost as frequently as men. However, men are usually unable to disguise it as effectively as women because they tend to lose more hair and tend to have fewer styling options. Men with this condition may begin losing hair as early as their 20s, while women usually do not experience significant hair loss or thinning until their 40s or later. Androgenetic alopecia in men is distinguished by a receding hairline and the disappearance of hair from the crown (top of head), forming a bald spot. Women tend to experience a general thinning throughout the scalp and may lose hair at the crown as well, though not as significantly as men. People with this form of hair loss have some hair follicles (tiny, tubular structures in the skin through which hair grows) with a shorter than normal hair growth phase, producing hairs that are shorter and thinner than normal. This is thought to occur as a result of hormonal changes in the follicle itself.
  
  
• Telogen effluvium. Widespread hair loss across the scalp. It usually is characterized by temporary or reversible loss of hair, usually following a highly stressful event. Telogen effluvium causes hair throughout the scalp to shed prematurely, in contrast to normal hair loss, which occurs in a staggered fashion. This type of hair loss may not be noticeable until a significant amount of hair is missing. Hair regrowth should begin about three to four months after the triggering event. Common triggers of the condition may include pregnancy, surgery or illness and psychological trauma. In addition, many medical conditions (e.g., nutritional deficiency, syphilis) and medications (e.g., antidepressants) may cause hair loss. In women, this condition can be difficult to distinguish from androgenetic alopecia.
  
  
• Traumatic alopecia. Hair loss that is caused by chemicals (e.g., bleach, hot oils) or styling techniques that apply constant tension to the hair (e.g., hair straightening, tight braids). Habits of consistently altering hair (e.g., twisting, plucking) can cause hair to be distributed unevenly or broken. Traumatic alopecia is usually confined to the area being styled. It is often reversible but may become permanent if the area becomes scarred.
  
  
• Alopecia areata. Patchy baldness. This form of hair loss may also occur on other areas of the body (e.g., face). This form of hair loss may also occur on other areas of the body (e.g., face). Alopecia areata is an autoimmune disease (a condition in which the body's immune system attacks its own cells), which develops in people who are usually in good health otherwise. The cause of alopecia areata is unknown, though research suggests that some people may be genetically predisposed and some type of trigger (e.g., virus, stress) may activate it internally. Patients with alopecia areata often lose and regrow hair repeatedly.

Scarring hair loss occurs at scarred or damaged areas of the scalp and is much less common than nonscarring hair loss. It is usually caused by trauma (e.g., burns, physical injury) but may be caused by disease as well (e.g., skin cancer, lupus). Once an area of the scalp is fully scarred, hair regrowth is highly unlikely.

Hair loss (alopecia) is defined as losing enough hair that a person has visibly thin or balding patches. The most common causes of hair loss include:

• Heredity. The most common cause of hair loss in both men and women. A history of hereditary hair loss (e.g., androgenetic alopecia, alopecia areata) from either side of the family greatly increases an individual’s likelihood of experiencing hair loss. Heredity often affects the age at which hair loss begins, speed of progression, pattern and extent. At a predetermined point, heredity triggers the production of an enzyme (complex proteins found in body cells that enable chemical reactions to take place) called 5-alpha reductase. When the male sex hormone testosterone combines with this enzyme, dihydrotestosterone (DHT) is produced. DHT causes both the affected hair follicle (tiny, tubular structure in the skin through which hair grows) and hair to shrink in size, causing hair to thin or permanently fall out.
  
  
• Trauma. A frequent cause of hair loss in women and children. Trauma to hair follicles may be caused by the act of drawing or pulling the hair (traction) for styling purposes (e.g., braids, ponytail), from heat (e.g., blow-drying) or self-induced pulling habits (trichotillomania). Excessive shampooing, brushing or combing can also damage hair, resulting in breakage. Hair loss from trauma is often reversible but may become permanent if trauma continues. An exception is physical trauma to the scalp (e.g., burns), which can cause scarring or damage to hair follicles, often making hair regrowth impossible or unlikely.
  
  
• Hormones. Patterned hair loss in both men and women occurs, in part, because of sensitivity of the affected hair follicles to androgen (male sex hormone) production levels. Various hormonal conditions can also interfere with the normal cycle of hair growth and cause hair loss (e.g., high levels of thyroid hormones). Hormonal changes due to polycystic ovarian syndrome (a condition in which androgens are overproduced by the ovaries) and use of birth control pills can cause hair loss in women.
  
  
• Disease or illness. A variety of common diseases (e.g., cancer, diabetes, kidney or liver disease) may cause hair loss in patients. Skin infections (e.g., ringworm) can invade the hair and skin of the scalp and cause hair loss. However, follicles typically have the potential to regrow hair if it is lost due to disease or illness.
  
  
• Medications. Numerous medications may cause hair loss as a side effect (e.g., chemotherapy drugs, arthritis drugs, high blood pressure drugs, gout drugs, anticoagulants, antidepressants, lithium [a mood stabilizer]). The degree to which hair loss is experienced varies, depending on the drug or medication being administered and the nature of the underlying medical condition.
  
  
• Stress. The body’s response to a physically or emotionally stressful event (e.g., pregnancy, menopause, surgery, high fever, severe flu) may initiate hair loss in some people. Following a stressful event, hair shifts into a resting (telogen) phase prematurely. This reduces the amount of new hairs that are grown, sometimes causing abnormal hair loss. Although, any hair lost in this manner is usually temporary and grows back.
  
  
• Poor nutrition. Poor eating habits or eating disorders (e.g., anorexia nervosa, bulimia) can cause abnormal hair loss, in addition to other more serious medical conditions (e.g., low blood iron levels). People whose bodies do not receive enough vital nutrients such as protein or certain vitamins may experience abnormal thinning or loss of hair, regardless of age. Teenage or adolescent girls with poor body images experience hair loss from poor nutrition most frequently.
  
  
• Chemicals. Hair that is repeatedly treated with chemicals (e.g., dying, bleaching, straightening, perming) may break off or fall out. Hair loss as a result of chemicals is usually reversible but may be permanent in some cases if scarring occurs.

A number of events or circumstances can interrupt the normal cycle of hair growth and cause excessive hair loss, including heredity, hormones and medication. Hair loss may be temporary or permanent depending on the cause.

About half of the hairs in an affected area need to be shed before hair loss is typically noticeable. However, when this occurs, excessive hair loss is usually visually apparent. An unusually high number of hairs discovered on a pillow or hairbrush are also common indicators that abnormal hair loss may be occurring. Androgenetic alopecia in men (male pattern hair loss) may begin as early as the teenage years (premature male pattern hair loss) and is typically defined by hair loss around the temples and crown area. This may result in partial (receding hairline) or complete baldness.

Androgenetic alopecia in women (female pattern hair loss) tends to cause less hair loss, usually consisting of thinning near the front or side areas. Women with female pattern baldness rarely go completely bald and do not usually experience any significant hair loss until around the time of menopause.

Alopecia areata (patchy baldness) usually occurs in small areas on the scalp and sometimes on other areas of the body such as the face. Hairs that are easily pulled or tugged out of the scalp without resistance often indicate the presence of alopecia areata.

Hair loss that occurs in conjunction with an unusually stressful event (e.g., pregnancy, menopause) or serious medical condition (e.g., cancer) is usually reversible and may indicate telogen effluvium (hair loss following a stressful event).

Hair loss is not usually a cause for concern. However, it can be an early sign of certain diseases (e.g., diabetes, systemic lupus erythematosus, thyroid disorders). Hair loss may also develop as the result of poor nutrition (e.g., iron deficiency), skin damage or as a side effect of certain medications.

In general, individuals should consult a dermatologist if any of the following occurs:

• Rapid hair loss
• Hair loss in patches
• Hair loss at an early age (e.g., teenage years, 20s)
• Hair loss begins soon after starting a new medication
• Facial hair loss (e.g., balding on beard or eyebrows)
• Hair loss with itching, skin irritation, redness, scaling, pain or other abnormalities

Hair loss (alopecia) is defined as losing enough hair that a person has visibly thin or balding patches. In order to diagnose hair loss, a physician will obtain the patient’s complete medical history, including recent or past illnesses and current medications, and review any family history of hair loss. Patients may also be questioned about their diet and hair care habits (e.g., dying, blow drying). Female patients may also be asked about menstrual cycles, pregnancy history and menopause. In addition, the physician will perform a physical examination, during which he or she will observe the total amount of hair on the scalp and analyze how it is distributed.

Men with androgenetic alopecia (pattern hair loss) usually lose hair on the crown of the scalp and around the temples, making diagnosis relatively routine. Women with androgenetic alopecia usually lose hair on the crown, starting with a widening of the part of the hair. 

Additional testing may be performed (e.g., skin biopsy) to check if other hair conditions (e.g., alopecia areata, telogen effluvium) or certain illnesses that cause hair loss may be responsible or occurring in conjunction with hair loss. Skin infections that may cause hair loss (e.g., ringworm) can be diagnosed by examining skin samples from the scalp. Examining pulled hair for differences in thickness and length may also help confirm a diagnosis.

In cases of severe hair loss with signs of accompanying illness, a variety of blood tests or imaging tests may be used to determine if an underlying condition or disease is responsible or occurring in conjunction with hereditary hair loss. Numerous medications have side effects that may cause hair loss, including anticoagulants (decrease blood clots), anticonvulsants (treat seizures), beta blockers (lower blood pressure) and antidepressants (treat depression).

Charts depicting different types of hair loss information may be used in some cases. However, they are insufficient to diagnose what may be responsible. The Hamilton-Norwood classification chart breaks down the progression of male pattern hair loss into seven classes. Initial hair loss (stages 1 and 2) typically consists of a receding frontal hairline. This recession becomes more defined over the temples and crown area of the scalp in the intermediate period (stages 3 through 5). Finally, total hair loss over the top and upper sides and back of the scalp characterizes the most advanced progression of the condition (stages 6 and 7). Modified versions of the system may be used for patients with different balding patterns.

The Ludwig classification system may also be used to describe levels of female pattern hair loss. The Ludwig system organizes levels of hair loss in the following manner:

• Grade I. Minimal widening of the hair part.
  
• Grade II. Moderate thinning or widening of the part.
  
• Grade III. Extensive thinning and widening of the part.

Hair loss (alopecia) is not a serious medical condition in itself. Therefore, treatment may not be necessary. In fact, many people choose to let the condition run its course.

There is no cure for hair loss. However, treatments are available that may grow hair or slow loss, with medications being the most widely used. The following medications are approved to treat hair loss by the U.S. Food and Drug Administration (FDA):

• Minoxidil. An over-the-counter liquid or foam that is rubbed into the scalp twice daily. It must be used for several months before the patient sees any results. Minoxidil may be effective at treating androgenetic alopecia (pattern hair loss), and help minimally with alopecia areata (patchy baldness), by reversing the shrinking process that occurs in the hair follicle (tiny, tubular structure in the skin through which hair grows) and stimulating new hair growth. Minoxidil is the only over-the-counter treatment approved by the FDA for use in women. The drug may be used in conjunction with other treatments. Any benefit derived from minoxidil usually ceases once use is discontinued.
  
  
• Finasteride. A prescription medication taken orally to treat male pattern baldness. Finasteride may slow or stop hair loss in some patients. In addition, others may see hair growth after continued use. Finasteride inhibits the body’s ability to convert testosterone into dihydrotestosterone (DHT), the hormone that shrinks hair follicles and contributes significantly to hair loss. Like minoxidil, any benefits derived from the drug stop once use is discontinued. Finasteride is not approved for use by women because it is ineffective in women and poses the risk of serious birth defects in male fetuses.
  
  
• Corticosteroids. Injections of cortisone in areas of the scalp where hair is being lost abnormally. Corticosteroid injections are frequently used to treat cases of moderate alopecia areata. For more severe cases, corticosteroids may be given orally to treat the disease. In some instances, ointments and creams may be used, though they may not work as well.
  
  
• Anthralin. A synthetic substance that is applied and washed off the scalp daily. Anthralin is usually used to treat psoriasis (chronic condition marked by frequent episodes where the skin becomes itchy and red and develops thick, dry, silvery scales), but it may stimulate hair growth in patients with alopecia areata.

In addition to medication, surgical procedures are available to treat hair loss (e.g., hair transplants).

Nonmedical methods such as wigs, hairpieces and weaves are also available to effectively disguise hair loss. These may be made with either real or synthetic hair and are often the least expensive treatment method. In some cases, hairstyle changes can also help disguise the condition. However, these methods do not slow or stop the progression of further hair loss.

Often, the ability to prevent or stop hair loss largely depends on the underlying cause. Loss of hair due to a stressful event or disease (telogen effluvium) does not usually persist long after the event or disease has ended or been removed. Hair loss caused by medication is also reversed once the medication is discontinued.

Non-hereditary hair loss is far less common but often much more easily preventable. Hair loss caused by chemicals (e.g., bleach, hot oils) or styling techniques that apply constant tension to the hair (e.g., hair straightening) can often be eliminated or minimized by simply changing the style responsible. However, hair regrowth is highly unlikely if scarring of the scalp occurs as a result of hair styling, hair pulling or trauma (e.g., burn).  

Hair loss caused by heredity (e.g., androgenetic alopecia, alopecia areata) is incurable. However, the medications used to treat the condition may prevent further hair loss or regrow hair if their use is initiated in the early phases of hair loss.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctors the following hair loss-related questions:

1. What may be causing my hair loss?
   
   
2. Should I be tested for a disease that may be causing my hair loss?
   
   
3. How extensive will my hair loss be?
   
   
4. How likely am I to have hair regrowth?
   
   
5. What are my treatment options?
   
   
6. Is hair transplantation something I should consider?
   
   
7. Will the results of my treatment be permanent?
   
   
8. Will I pass my baldness on to my kids?