What Causes Alopecia (Hair Loss)?

There are many causes of alopecia (hair loss), including trauma, medications, fungal infections, and genetics. Alopecia is a group of conditions that affects the hair follicles, or the pores in your skin where hair grows. Damage to the hair follicles can result in partial or complete hair loss.

Some forms of alopecia may be autoimmune disorders, meaning the immune cells attack the hair follicles. It isn't clear exactly what causes these disorders in the first place.

Causes by Type of Hair Loss

Different types of stressors cause many forms of hair loss. Drug treatments, physiological or emotional stress, hormonal changes, infection, and even hairstyles can cause hair to fall out.

These forms of alopecia are generally non-scarring alopecia, meaning they don't cause permanent damage (scarring) to the hair follicles. The hair may regrow once the cause of the hair loss is addressed.

Anagen Effluvium

Chemotherapy, or a type of drug that kills cancer cells, can cause a form of alopecia called anagen effluvium. The chemotherapeutic agent causes the hair to fall out from the root.

People with cancer and who undergo chemotherapy may begin to have hair fall out within the first two weeks of treatment. The hair mostly regrows once the treatment finishes.

Androgenetic Alopecia

The most common form of alopecia is a genetic condition called androgenetic alopecia. People with this type of hair loss may inherit certain genes that lead to excess androgen hormone production (e.g., testosterone). Excess androgens then play a role in causing hair loss.

People with the genes for androgenetic alopecia have hair follicles that are more sensitive to the effects of these androgens. Symptoms can be different across the sexes. This type of alopecia might sometimes be called male- or female-pattern hair loss.

Telogen Effluvium

Telogen effluvium is hair loss caused by physiological or emotional stress. These stressors cause changes in hormonal or stress-related pathways that cause sudden hair loss. The hair falls out in excess around all areas of the scalp, which may be noticeable while showering or brushing. Addressing the underlying cause of the stress can stop hair loss.

Some of the underlying stressors may include:

• Childbirth
• Fever (febrile illness)
• Hormonal disorders (e.g., thyroid disorder)
• Inflammatory scalp conditions, such as seborrheic dermatitis (a type of scalp eczema) or psoriasis (an autoimmune skin condition)
• Nutritional deficiencies due to an underlying condition, such as iron deficiency anemia (lack of iron due to low red blood cell count) 
• Restrictive diets
• Scalp infection due to bacteria, viruses, or fungi 
• Sudden illnesses or long-term medical conditions
• Sudden weight loss
• Traumatic events

Tinea Capitis

Hair loss can happen due to various infections. One type of fungal infection that can damage the hair follicles is called tinea capitis (ringworm of the scalp). This infection leads to a patchy pattern of hair loss and sometimes scaly skin on the scalp. 

Some forms of tinea capitis can cause inflammation of the hair follicle, resulting in scarring and permanent hair loss. Other forms that don't cause inflammation are non-scarring and tend to cause temporary hair loss. Treating the infection with antifungals can help stop hair loss.

Traction Alopecia

Excessive brushing or prolonged tension can damage the hair, causing traction alopecia. Hairstyles like braids or weaves also damage hair follicles and cause hair loss.

Addressing the causative factor will prevent continual alopecia and allow hair to regrow. If traction alopecia is left untreated for too long, the follicles may be permanently damaged, and hair may not regrow.

Trichotillomania

Trichotillomania is a mental health condition and type of alopecia. People with this condition have a compulsive urge to pull out hair, leading to thinning and uneven bald patches. Trichotillomania can also affect hair on other regions of the body, including eyelashes, eyebrows, and pubic hair.

Theories by Type of Hair Loss

Scientists are certain that the immune system plays a role in some rarer forms of alopecia. However, it isn't clear exactly what the underlying cause is. An underlying immune disorder or white blood cells sometimes damage the hair. These forms of alopecia are often scarring, meaning they damage the hair follicles, preventing regrowth.

Alopecia Areata

Alopecia areata is a type of hair loss that researchers suspect may be an autoimmune disorder. Immune cells attack the hair follicles. Certain genetic variants are also associated with this type of alopecia.

Alopecia areata causes hair loss on the scalp and face, characterized by small, round patches of hair falling out. It can also affect hair follicles in other parts of the body. Most people are able to regrow their hair, while some others aren't.

Central Centrifugal Cicatricial Alopecia (CCCA)

Central centrifugal cicatricial alopecia (CCCA) is a form of alopecia that may be inherited in families. The exact cause of this alopecia is not fully understood.

CCCA causes a circular bald patch to form on top of the head. This circular patch continues to spread over time, causing scarring and permanent hair loss. Treatment may slow down the growth of the bald patch.

Lichen Planopilaris (LPP)

Lichen planopilaris (LPP) is a type of alopecia that causes inflammation and scarring in the hair follicles. The cause of LPP is unclear, but scientists believe lichen planus may be responsible. Lichen planus may occur when certain triggers activate immune cells in the hair follicles. 

These triggers may include: 

• Antimalarials, or drugs that treat malaria
• Certain viruses, like hepatitis C virus (HCV), human immunodeficiency virus (HIV), herpes simplex virus type 2 (HSV-2), and human papillomavirus (HPV)
• Certain medications to treat blood pressure, including beta-blockers, angiotensin-converting enzyme (ACE) inhibitors, and thiazide diuretics
• Contact allergens (e.g., gold, mercury, and cobalt)
• Syphilis, a sexually transmitted infection (STI) caused by a bacteria called Treponema
• pallidum

Immune cells may become overactivated, leading to hair loss in band-like patterns. Scarring tissue replaces the affected hair follicles, and the hair does not grow back. 

Frontal Fibrosing Alopecia

Frontal fibrosing alopecia is a form of LPP. This form of hair loss scars the scalp. People with frontal fibrosing alopecia have symmetric bands of patches near the front of the hairline, but it may spread to other regions. Scientists suspect that immune cells attack the hair follicles. More research is needed to determine the cause. 

Is Hair Loss Hereditary?

Not all forms of alopecia are genetic. Genetic factors may play a role in causing androgenetic alopecia and are also associated with forms of alopecia that may be caused by immune dysfunction.

Hair loss likely develops due to a combination of factors. These factors include other health conditions, environmental factors like stress, and genetic factors.

Androgenetic Alopecia

The pattern of inheritance isn't clear. If androgenetic alopecia runs in the family, you are more likely to develop it. Men with fathers who had male-pattern hair loss are over five times more likely to develop it than men with fathers without the condition.

Researchers have not identified specific genes linked to male- or female-pattern hair loss. Variants in these two genes are strongly linked to male-pattern hair loss:

• 5-alpha reductase type II (SRD5A2): This gene encodes a protein that helps make androgens. Some variants may make this protein more efficient, leading to more androgens and hair loss.
• Androgen receptor (AR): This gene corresponds to a protein that responds to androgens. Some variants can make the androgen receptor more reactive, which may lead to androgenetic alopecia.

Alopecia Areata

Alopecia areata may involve a genetic risk. Several genetic polymorphisms, or specific variants of certain genes, are linked to a high risk of this condition.

These genes include:

• IL-12b (Il12b): This gene encodes a cytokine (a type of protein) that stimulates other immune cells. Certain variants of this gene (CC variants) are associated with a high risk of late-onset alopecia areata (i.e., after age 50).
• IL-23R (Il23r): This gene encodes a receptor that helps activate other immune cells. Certain gene variants (AA variants) are linked to a high risk of late-onset alopecia areata.
• Major histocompatibility complex (MHC): This group of genes encodes proteins on your immune cells and helps the immune system recognize itself. Variants of genes within this group, including HLA-DRβ1 and CCHCR1, are linked to an increased risk of alopecia areata.

Frontal Fibrosing Alopecia (FFA)

Variants in immune-related genes are implicated in frontal fibrosing alopecia. About 8% of cases of FFA are linked to a family history of FFA. Many of these variants are within the genes for the MHC.

The gene variants may make the immune system less likely to recognize hair follicles as part of the body. These variants include:

• 2p22.2: This variant causes one of the proteins involved in processing androgens, CYP1B1, to malfunction. 
• 6p21.1: This variant confers the largest risk of frontal fibrosing alopecia. 6p21.1 affects the HLA gene, which prevents immune cells from attacking the body.
• 8q24.22: This variant is associated with a gene called ST3GAL1, which may make T-cells (a white blood cell) more likely to attack hair follicles.
• 15q2.1: This variant affects how much SEMA4AB protein is produced. It isn't clear why it increases the risk of frontal fibrosing alopecia.

Central Centrifugal Cicatricial Alopecia (CCCA)

Genetic variants of PADI3 are linked to CCCA. This gene encodes a protein that forms the hair shaft. Certain variants can affect how well this protein can do its job. Other genes may be linked to CCCA. More research is needed to identify them. 

Who Gets Hair Loss?

Some forms of alopecia are more common than others:  

• Alopecia areata: This can affect any race, age, and sex, with no significant difference in rate. Approximately 0.2% of the population gets this form of hair loss.
• Anagen effluvium: This is most common in people who are taking chemotherapy and radiation therapy to treat cancer. These treatments can kill cancer cells but temporarily prevent hair from growing. 
• Androgenetic alopecia: This affects more than 50% of men, occurring anytime after puberty. This type of hair loss also affects 15% of women after menopause. Androgenetic alopecia is most common in White people.
• Central centrifugal cicatricial alopecia (CCCA): This is most common in Black women. Hair loss generally begins between the ages of 30–55. 
• Frontal fibrosing alopecia (FFA): This is most likely to occur in Black women. The condition tends to start after age 50.
• Lichen planopilaris (LP) is common in women between the ages of 40 and 60. However, people can still develop this form of alopecia earlier in life. 
• Telogen effluvium: This is most common to a birthing parent three months after childbirth. This form of hair loss may also occur in people who have experienced traumatic events, sudden changes in diet, or serious illness.
• Tinea capitis: Anyone can develop this form of hair loss from ringworm. Tinea capitis occurs most commonly in non-White children. All genders are equally as likely to develop this condition.
• Traction alopecia: This often occurs in populations and ethnicities that wear hairstyles that cause hair tension. This hair loss is most commonly diagnosed in Black women in the United States. 
• Trichotillomania: This is four times more likely to occur in women. Trichotillomania is most likely to affect people with underlying health problems that impact their impulse control.

Risk Factors

Several environmental factors can contribute to alopecia. These factors include mental health, diet, childbirth, and medications. 

Diet

Nutrients play important roles in hair follicle development and immune function. Having protein, vitamin, and mineral deficiencies in the diet can put people at greater risk of alopecia.

These include:

• B vitamins (e.g., B12, folate, and riboflavin)
• Biotin
• Iron
• Selenium
• Vitamin A (excess vitamin A is also a known cause of hair loss)
• Vitamin C
• Vitamin D
• Vitamin E
• Zinc 

Mental Health

Stressful events may increase the risk of hair loss later in life. Mental health conditions and experiences linked to alopecia include emotional trauma, obsessive-compulsive disorder (OCD), anxiety, bipolar disorder, schizophrenia, and depression, which can contribute to emotional distress.

Certain health concerns can be more directly linked to specific subtypes of alopecia. OCD and trichotillomania, for example, are more likely to overlap.

Medications

Many different medications can increase the risk of alopecia, including:

• Anti-clotting drugs: This class of drugs may lead to telogen effluvium. It's not known why. Some common anti-clotting drugs include Coumadin (warfarin), Jantoven (warfarin), Lovenox (enoxaparin), Fragmin (dalteparin), and Innohep (tinzaparin).
• Antidepressants: It isn't clear why, but these drugs that treat depression can cause telogen effluvium. Some examples include tricyclic antidepressants, such as Tofranil (imipramine) and Norparmin (desipramine), which can cause alopecia. Selective serotonin reuptake inhibitors (SSRIs) that may lead to hair loss include Zoloft (sertraline), Aropax (paroxetine), Prozac (fluoxetine), and Celexa (citalopram). The hair usually regrows within a year. 
• Blood pressure drugs: A class of these drugs called beta-blockers may lead to hair loss. These drugs can disrupt hair follicle growth, leading to telogen effluvium. Examples include Lopressor (metoprolol), Inderal (propranolol), and Corgard (nadolol). Not all beta-blockers may lead to hair loss. Lasix (furosemide), for example, is not associated with alopecia. 
• Chemotherapy: Drugs like Busulfex (busulfan) can stop hair from growing, causing anagen effluvium in up to half of people with cancer.
• Combined birth control pills: This type of contraception contains doses of the sex hormones estrogen and progestin (a synthetic type of progesterone). These drugs may trigger changes in the hair, shifting it from the growth to the resting phase, leading to telogen effluvium. Examples include Amethyst (estradiol and levonorgestrel) and Estarylla (ethinyl estradiol and norgestimate). These drugs can worsen or trigger the onset of androgenetic alopecia.
• Mood stabilizers: Some drugs that treat mental health conditions like bipolar disorder or schizophrenia may cause telogen effluvium. Many of these treatments affect thyroid metabolism, which may explain this side effect. Priadel (lithium), Belvo (valproic acid), Haldol (haloperidol), Risperdal (risperidone), Zyprexa (olanzapine), and Tegretol (carbamazepine) can cause hair loss.

If you have hair loss and suspect it's a side effect of a medication, visit a healthcare provider to discuss whether a change in your treatment regimen is needed. They can provide treatments for alopecia. 

Childbirth

The levels of the sex hormone estrogen drop after childbirth, leading to hair shedding. As estrogen levels return to baseline, hair will typically regrow within a year.

A Quick Review

There are several types of alopecia, which are conditions involving partial or complete hair loss. Different types of alopecia have different causes, such as physiological or emotional stress, infection, chemotherapy, or excess hair tension.

The cause may not be known for other types of alopecia. It's possible an altered immune response may be involved. A combination of genetic and other environmental risk factors can increase a person's risk of alopecia.