Alopecia refers to a group of conditions that affect the hair follicles—structures in the skin where hair grows. These conditions can result in partial or total hair loss. Causes include trauma, genetics, infections, medications, and immune system dysfunction. In some cases, the immune system mistakenly attacks hair follicles, leading to autoimmune-related alopecia.

Causes by Type of Hair Loss

Hair loss can occur due to various physical, emotional, hormonal, or external stressors. Most of these conditions result in non-scarring alopecia, where hair follicles are not permanently damaged and hair may regrow when the underlying cause is addressed.

Anagen Effluvium

chemotherapy drugs can trigger this type of hair loss. These medications target fast-growing cells, including those in hair follicles. Hair loss may begin within weeks of starting treatment and usually reverses after therapy ends.

Androgenetic Alopecia

genetic predisposition and hormones play major roles in this form. People inherit genes that make their follicles more sensitive to androgens (male hormones), leading to progressive thinning of the hair. This condition is also known as male-pattern or female-pattern hair loss.

Telogen Effluvium

physical or emotional stress disrupts the hair growth cycle, pushing hair into the resting (telogen) phase prematurely. Hair shedding typically appears all over the scalp.

common triggers include:

  • Childbirth

  • Fever or illness

  • Thyroid disorders

  • Scalp conditions like seborrheic dermatitis or psoriasis

  • Nutritional deficiencies (e.g., iron)

  • Rapid weight loss

  • Restrictive diets

  • Infections

  • Traumatic events

Addressing the stressor often leads to regrowth.

Tinea Capitis

fungal scalp infection can damage follicles, leading to patchy hair loss and flaky scalp. Some forms cause inflammation and scarring, while others result in temporary hair loss. Antifungal treatments are typically effective.

Traction Alopecia

tension from hairstyles like braids or tight ponytails can damage follicles. Early intervention allows regrowth, but prolonged stress may result in permanent hair loss.

Trichotillomania

compulsive hair pulling characterizes this mental health condition. It results in patchy hair loss on the scalp, eyebrows, eyelashes, and body. The severity can vary based on psychological factors.

Theories by Type of Hair Loss

Some types of alopecia appear to involve the immune system. Immune cells may attack hair follicles, resulting in scarring and irreversible hair loss. These forms are often harder to treat and may have genetic components.

Alopecia Areata

autoimmune-related hair loss where immune cells attack hair follicles. Hair usually falls out in small, round patches. Some people experience full regrowth, while others may not.

Central Centrifugal Cicatricial Alopecia (CCCA)

scarring hair loss often begins at the crown of the head and spreads outward. This form may run in families and causes permanent damage if not treated early.

Lichen Planopilaris (LPP)

inflammation and immune response may be triggered by infections, medications, or allergens. Follicles become scarred, preventing hair from regrowing.

potential triggers include:

  • Antimalarial medications

  • Viral infections (e.g., hepatitis C, HIV)

  • Certain blood pressure medications

  • Contact allergens (e.g., metals)

  • Autoimmune diseases like lichen planus

Frontal Fibrosing Alopecia (FFA)

a type of LPP, this condition causes hair loss in bands at the hairline and may extend to other body areas. The exact cause remains unknown, but immune system involvement is suspected.

Is Hair Loss Hereditary?

Some forms of alopecia, like androgenetic alopecia, are strongly linked to family history. Others, such as autoimmune-related types, may also involve genetic susceptibility. However, alopecia usually develops due to a combination of genetic and environmental factors.

Androgenetic Alopecia

inherited genetic traits increase sensitivity to androgens. Men with a family history are more likely to experience male-pattern hair loss. Specific gene variants associated with this form include:

  • 5-alpha reductase type II (SRD5A2): may increase androgen production

  • Androgen receptor (AR): may amplify the follicle's response to androgens

Alopecia Areata

genetic polymorphisms are linked to higher risks, particularly those affecting immune system function. These genes may trigger immune cells to attack follicles:

  • IL-12b: associated with late-onset alopecia

  • IL-23R: regulates immune responses

  • MHC complex: involved in immune recognition

Frontal Fibrosing Alopecia (FFA)

gene variants related to immune function may impair the body’s ability to protect its hair follicles. Known variants include:

  • 2p22.2 (CYP1B1): affects androgen metabolism

  • 6p21.1 (HLA genes): weakens immune self-recognition

  • 8q24.22 (ST3GAL1): increases follicle attack by immune cells

  • 15q2.1 (SEMA4AB): function unknown but linked to risk

Central Centrifugal Cicatricial Alopecia (CCCA)

PADI3 gene mutations impair hair shaft formation. This genetic variation has been linked to CCCA. Ongoing studies aim to identify additional related genes.

Who Gets Hair Loss?

Different types of alopecia affect specific groups:

  • Alopecia areata: all ages, sexes, and ethnicities

  • Anagen effluvium: people receiving chemotherapy

  • Androgenetic alopecia: more than 50% of men and 15% of postmenopausal women

  • CCCA: common in Black women ages 30–55

  • FFA: usually affects Black women over 50

  • LPP: often seen in women between ages 40–60

  • Telogen effluvium: common after childbirth or major stress

  • Tinea capitis: often affects non-White children

  • Traction alopecia: most frequent in individuals who wear tight hairstyles

  • Trichotillomania: more likely in women and linked to impulse control disorders

Risk Factors

Multiple environmental and health-related factors can contribute to hair loss.

Diet

nutrient deficiencies affect follicle health and immune function. Lacking the following can increase hair loss risk:

  • B vitamins (B12, folate, riboflavin)

  • Biotin

  • Iron

  • Selenium

  • Vitamin A (excess is also harmful)

  • Vitamin C

  • Vitamin D

  • Vitamin E

  • Zinc

Mental Health

emotional trauma and mental health disorders can lead to alopecia. Stress is a known trigger for telogen effluvium and may worsen autoimmune forms. Conditions like OCD, anxiety, bipolar disorder, and depression are also linked.

Medications

several medications can cause hair loss, typically via telogen effluvium or growth disruption:

  • Anticoagulants (e.g., warfarin, enoxaparin)

  • Antidepressants (e.g., imipramine, paroxetine, fluoxetine)

  • Beta-blockers (e.g., metoprolol, propranolol)

  • Chemotherapy drugs (e.g., busulfan)

  • Birth control pills (e.g., levonorgestrel, ethinyl estradiol)

  • Mood stabilizers (e.g., lithium, valproic acid, risperidone)

If hair loss is suspected to be medication-related, consult a healthcare provider.

Childbirth

postpartum hormone shifts, especially decreased estrogen, may lead to temporary hair loss. Most hair regrows within one year as hormone levels normalize.

A Quick Review

Alopecia can be caused by stress, genetics, infections, medications, or immune conditions. Some forms are reversible, while others cause permanent damage. Early diagnosis and understanding the underlying cause are essential for managing hair loss effectively.