What Causes Alopecia?

Alopecia is a group of conditions that affects the hair follicles—the pores in your skin where hair grows. It is characterized by partial or complete hair loss. There are many causes of alopecia including trauma, medications, fungal infections, and genetics. Some forms of alopecia may be autoimmune conditions, meaning the immune cells attack the hair follicles—but it isn’t clear exactly what causes them in the first place.

Causes by Type of Alopecia

Many forms of hair loss are caused by different types of stressors. 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 so the hair may regrow once the cause of the hair loss is addressed.

Anagen Effluvium

Chemotherapy, 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 that undergo chemotherapy may begin to have hair fall out within the first two weeks of starting treatment. In most cases, the hair can regrow once the treatment finishes.

Androgenetic Alopecia

The most common form of alopecia is a genetic condition called androgenetic alopecia. People with this type of alopecia may inherit certain genes that lead to excess androgen hormone production (like testosterone), which then plays a role in causing hair loss. People with the genes for androgenetic alopecia also have hair follicles that more more sensitive to the effects of these androgens. Symptoms can be different across sexes, so this type of alopecia might sometimes be called male-pattern hair loss 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 the hair loss.

Some of the underlying stressors may include:

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

Tinea Capitis

Hair loss can also happen due to various infections. One type of fungal infection that can damage the hair follicles is called tinea capitis—known commonly as 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 causing 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 Alopecia

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. Sometimes, an underlying immune disorder or white blood cells will damage the hair. These forms of alopecia are often scarring, meaning that they damage the hair follicles, preventing regrowth.

Alopecia Areata

Alopecia areata is a type of hair loss that researchers suspect may be an autoimmune condition—where immune cells attack the hair follicles. Having certain genetic variants is also associated with this type of alopecia. It causes hair loss on the scalp and face and is characterized by small round patches of hair falling out. It can also affect hair follicles on 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, though the exact cause of this alopecia is not fully understood. CCCA causes a circular bald patch to form on top of the head. Over time, this circular patch continues to spread, and the condition causes scarring and permanent hair loss. But treatment may help slow down the growth of the bald patch.

Lichen Planopilaris (LPP)

Lichen planopilaris (LPP) is a type of alopecia characterized by inflammation and scarring in the hair follicles. While the cause of LPP is unclear, scientists believe that an underlying condition called lichen planus may be responsible. Lichen planus may occur when immune cells in the hair follicles are activated by certain triggers.

These triggers may include:

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

The immune cells may become overactivated, leading to hair loss in band-like patterns. The affected hair follicles are then replaced by scarring  tissue, and the hair does not grow back. 

Frontal Fibrosing Alopecia

Frontal fibrosing alopecia is considered to be a form of Lichen planopilaris. It is a form of hair loss that scars the scalp. It leaves characteristic symmetric bands of patches near the front of the hairline though it may spread to other regions. Scientists suspect that immune cells attack the hair follicles, though more research is needed to determine the cause. 

Is Alopecia Genetic?

Not all forms of alopecia are genetic. However, genetic factors may play a role in causing androgenetic alopecia. There are also genetic factors associated with forms of alopecia that may be caused by immune dysfunction. But it’s likely that these conditions develop due to a combination of factors, such as other health conditions or environmental factors like stress, along with genetic factors.

Androgenetic Alopecia

While the pattern of inheritance isn’t clear, you are more likely to develop androgenetic alopecia if it runs in the family.

Men with fathers who had  male-pattern hair loss are over five times more likely to develop androgenetic alopecia, compared to men with fathers without the condition.

Variants in these two genes are strongly linked to male-pattern hair loss:

• Androgen receptor (AR): This gene corresponds to a protein that responds to a sex hormone called androgens. Some variants can make the androgen receptor more reactive, which may lead to androgenetic alopecia.
• 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 androgen production and more hair loss.

Currently, researchers have not identified any specific genes that are linked to male- or female-pattern hair loss.

Alopecia Areata

Alopecia areata may also involve a genetic risk. Several genetic polymorphisms—or, specific variants of certain genes—are linked to a higher likelihood of developing 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 developing late-onset alopecia areata (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 developing late-onset alopecia areata (after age 50).
• Major histocompatibility complex (MHC): This is a group of genes that encode proteins on your immune cells and help the immune system recognize itself. Variants of genes within this group including HLA-DRβ1 and CCHCR1 are linked to an increased risk of developing alopecia areata.

Frontal Fibrosing Alopecia (FFA)

Variants in immune-related genes are also implicated in frontal fibrosing alopecia. About 8% of cases of FFA are linked to a family history of FFA.

Many of these variants are found within the genes for the major histocompatibility complex (MHC), which is also linked to alopecia areata, as previously mentioned. The gene variants may make the immune system less likely to recognize hair follicles as part of the body. They include:

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

Central Centrifugal Cicatricial Alopecia (CCCA)

Genetic variants of PADI3 are linked to the development of CCCA. This gene encodes a protein that forms the hair shaft. Certain variants can affect how well this protein can do its job.

There may be other genes linked to this condition, though more research is needed to identify them. 

Who Gets Alopecia?

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.
• Androgenetic alopecia: This affects more than 50% of all people assigned male at birth, occurring anytime after puberty. It also affects 15% of people assigned female at birth after menopause. It is more common in white people of European ethnicities.
• Anagen effluvium: This is most common in people who are taking chemotherapy and radiation therapy to treat cancer. While these treatments can kill cancer cells, they temporarily prevent hair from growing. 
• Central centrifugal cicatricial alopecia (CCCA): This is most common in African Americans assigned female at birth. Hair loss generally begins between the ages of 30 and 55. 
• Frontal fibrosing alopecia (FFA): This is most likely to occur in people assigned female at birth from an African American background. The condition tends to start after a person reaches the age of 50.
• Lichen planopilaris (LP): This is common in people assigned female at birth 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. It may also occur in people who have experienced traumatic events, sudden changes in diet, or serious illness.
• Traction alopecia: This often occurs in populations and ethnicities that wear hairstyles that cause hair tension. In the U.S., it is most commonly diagnosed in African American women. In general, this alopecia is more common in women. 
• Tinea capitis: Anyone can develop this form of hair loss from a fungal infection of ringworm. However, it occurs most commonly in children belonging to non-white ethnicities. All genders are equally as likely to develop this condition.
• Trichotillomania: This is four times more likely to occur in people assigned female at birth. It is most likely to affect people with underlying conditions that impact their impulse control.

Risk Factors

There are several environmental factors that contribute to alopecia. These factors include mental health, diet, childbirth, and medications. 

Diet

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

• Vitamins A (excess vitamin A is also a known cause of hair loss)
• Riboflavin (Vitamin B2)
• Biotin
• Folate (Vitamin B9 and B12)
• Vitamin B12
• Vitamin C
• Vitamin D
• Vitamin E
• Iron
• Selenium
• 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, among other conditions that can contribute to emotional distress.

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

Medications

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

• Anti-clotting drugs: This class of drugs may lead to telogen effluvium, though it’s not known why. Some common anti-clotting drugs include Coumadin (warfarin), Jantoven (warfarin), Lovenox (enoxaparin), Fragmin (dalteparin), and Innohep (tinzaparin).
• Antidepressants: Though it isn’t clear why, these drugs to treat depression can cause telogen effluvium. Some examples include tricyclic antidepressants, such as Tofranil (imipramine) and Norparmin(desipramine) 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. 
• Combined birth control pills: This type of contraception contains doses of sex hormones, estrogen and progestin (a synthetic type of progesterone). They may trigger changes in the hair, shifting it from the growth phase to the resting phase, leading to telogen effluvium. Examples of these drugs include Amethyst (estradiol and levonorgestrel) and Estarylla (ethinyl estradiol and norgestimate). Sometimes, they can worsen or trigger the onset of androgenetic alopecia.
• Blood pressure drugs: A class of these drugs called beta-blockers may lead to hair loss by disrupting hair follicle growth, leading to telogen effluvium. Examples include Lopressor (metoprolol), Inderal (propranolol), and Corgard(nadolol). However, not all beta-blockers may lead to hair loss. For example, Lasix (furosemide) is also a diuretic, meaning it helps your body flush out salt and water; it is not associated with alopecia. 
• Chemotherapy: Drugs like Busulfex (busulfan) can stop hair from growing, causing anagen effluvium, in up to half of cancer patients.
• Mood stabilizers: Some drugs used to treat mental health conditions like bipolar disorder or schizophrenia may also 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) may cause hair loss.

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

Childbirth

After childbirth, the levels of the sex hormone estrogen drop leading to an increase in hair shedding. Hair will typically regrow within a year, as estrogen levels return to baseline.

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, though it’s possible that an altered immune response may be involved. In addition, a combination of genetic and other environmental risk factors can increase a person’s chances of developing alopecia.