Hair loss is a common problem that affects millions of people around the globe.

From alopecia to male pattern baldness and chemotherapy, hair loss comes in many forms—it’s a confusing and frustrating condition that can take a significant physical and emotional toll.

Some may find themselves gradually losing their locks over the years, while others may experience sudden, inexplicable bald spots on their scalp.


What Causes Hair Loss?


The human body is complex, and hair growth and loss are no exception. Many things can cause hair loss, including genetics, hormones, and aging. Hair loss has several other causes ranging from poor nutrition and autoimmune disorders to stress.



The most common cause of hair loss is genetics, which can lead to male-pattern baldness or female-pattern hair loss. Androgenetic alopecia is an autosomal dominant condition with hair loss characterized by a receding frontal hairline in men and diffuse hair thinning in women. Genetics accounts for around 80% of the predisposition to baldness. Genetic factors modify the intensity of the hair follicle response to circulating androgens. Boys with a strong predisposition can even go bald in adolescence.



Hormonal changes can play a role in hair loss by affecting the growth and lifespan of hair follicles. Specifically, hormones called androgens can contribute to hair loss in both men and women. Androgens are male sex hormones that are responsible for the development of male sexual characteristics, such as facial hair and a deeper voice. However, androgens can also contribute to hair loss in people who are genetically predisposed to hair loss.

In people with androgenetic alopecia, hair follicles become progressively smaller and shorter in the anagen phase, which is the active growth phase of the hair follicle. This results in thinner, shorter hair that eventually stops growing altogether. Androgens contribute to this process by binding to androgen receptors in the hair follicle, which can cause the follicle to shrink and produce thinner, shorter hairs. The hormone dihydrotestosterone (DHT), which is a byproduct of testosterone, is particularly implicated in male pattern baldness.

Imbalances in thyroid hormones can also contribute to hair loss, as they can affect the growth and development of hair follicles.

Medical Conditions


Several medical conditions can cause scarring and non-scarring alopecia.

Alopecia areata: This is an autoimmune disorder that causes hair loss in patches on the scalp or other parts of the body. The hair loss can be temporary or permanent. Alopecia areata affects up to 2% of the general population.

In those with this condition, the immune system mistakenly attacks the hair follicles, causing them to shrink and slow down hair production. The condition can occur at any age, but it most commonly affects teenagers and young adults.

Alopecia areata can cause hair loss in small, round patches on the scalp, or it can lead to more extensive hair loss, including complete loss of scalp hair, known as alopecia totalis, or complete loss of hair on the scalp and body, known as alopecia universalis. Hair loss can occur suddenly or gradually, and hair may regrow and fall out again in cycles.

Telogen effluvium: A type of hair loss that occurs when more hair follicles than normal enter the resting (telogen) phase of the hair growth cycle. This can lead to increased shedding of hair, often several months after a triggering event. Telogen effluvium is a common cause of hair loss and can affect both men and women of any age.

The triggering event that causes telogen effluvium can vary and may include:

  • Physical or emotional stress: illness, surgery, or a traumatic event
  • Hormonal changes: pregnancy or menopause
  • Medications: antidepressants or blood thinners
  • Nutritional deficiencies: iron or protein deficiency
  • Rapid weight loss or extreme dieting

The hair loss in telogen effluvium is typically diffuse and not localized to one specific area of the scalp. Hair may appear thinner overall, but there are typically no bald spots or patches. The shedding of hair may last for several months, but hair growth usually returns to normal once the underlying trigger is resolved.

Thyroid disorders: Both hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) can cause hair loss.

The thyroid gland produces hormones that regulate metabolism and other bodily functions, including hair growth. Thyroid disorders can lead to disruption of the normal hair growth cycle.  In hyperthyroidism, the thyroid gland produces too much thyroid hormone, which can speed up the hair growth cycle and lead to excessive shedding. In hypothyroidism, the thyroid gland does not produce enough thyroid hormone, which can slow down the hair growth cycle and lead to thinning and brittle hair.

Hair loss due to thyroid disorders may be diffuse, meaning it affects the entire scalp, or it may be patchy and occur in specific areas. Treatment for hair loss involves treating the underlying thyroid disorder.

Lupus: Systemic Lupus Erythematosus (SLE) or lupus is an autoimmune disorder that can cause hair loss as a symptom. Scalp discoid lupus erythematosus (DLE) occurs in 30%–50% of lupus patients. It is characterized by gradual or sudden hair loss, which may occur in patches, or diffuse hair thinning. The scalp is red, scaly, and thickened, and there may be visible scarring or skin lesions present.

Iron deficiency anemia: Iron is an essential mineral for the growth and maintenance of healthy hair. Without enough iron, the hair follicles may not receive enough oxygen and nutrients. This can lead to hair loss, as well as thinning and dryness of the hair. However, hair loss due to iron deficiency anemia is typically gradual and diffuse, rather than occurring in patches like some other types of hair loss. Hair may become brittle and break easily, and the scalp may be itchy or tender.

Scalp infections: Scalp infections can cause hair loss by damaging the hair follicles or disrupting the normal hair growth cycle. Fungal infections of the scalp, such as ringworm, are a common cause of hair loss due to scalp infections. Scalp ringworm (tinea capitis) can cause hair loss in circular patches on the scalp. The scalp may also be itchy, red, or scaly. Other scalp infections, such as bacterial or viral infections, can also cause hair loss in the same way. Hair loss due to scalp infections may be temporary and hair may regrow once the infection is treated.

Trichotillomania: This is a psychological disorder characterized by the urge to pull out one’s own hair, which can lead to hair loss. Trichotillomania is classified as an obsessive-compulsive and related disorder and can affect people of all ages, genders, and backgrounds.

It can result in loss in any hair-bearing area of the body, but it most commonly affects the scalp, eyebrows, and eyelashes. Hair pulling may be preceded by feelings of tension or anxiety, and it may provide a sense of relief or pleasure for some people.

Hair loss due to trichotillomania ranges from mild to severe, and it may be patchy or diffuse. In some cases, hair may regrow on its own, but in severe cases, permanent hair loss may occur.

Cancer: Chemotherapy and radiation therapy used to treat cancer can cause hair loss.


Medications, such as chemotherapy drugs or blood thinners, can cause hair loss as a side effect. These medicines include:

  • Chemotherapy drugs: interfere with the normal growth cycle of hair follicles
  • Anticoagulants: Blood-thinning medications, such as warfarin
  • Antidepressants: Serotonin reuptake inhibitors (SSRIs)
  • Anticonvulsants: Valproic acid and carbamazepine
  • Beta blockers: Metoprolol and propranolol
  • Retinoids: Vitamin A derivatives, such as isotretinoin
  • Steroids: Long-term use of steroids, such as prednisone



Emotional or physical stress can cause temporary hair loss. Cortisol, the stress hormone, is capable of disrupting the functioning and cyclic regulation of the hair follicle. Other stress-mediating substances such as substance P, adrenocorticotropic hormone, and prolactin can also inhibit the growth of hair.

Stress-related hair loss can be reversed through lifestyle changes such as relaxation techniques, like meditation, yoga, or deep breathing. It’s also important to maintain a healthy lifestyle, with regular exercise, a balanced diet, and adequate sleep, to help manage stress.


Hairstyles and Treatments


Certain hairstyles, such as tight braids or ponytails, and hair treatments, such as chemical straightening or hot oil treatments, place mechanical and chemical stress on hair follicles, damaging them and leading to hair loss.



The opinions shared in this article belong to the author and, like all content on Gambit’s Health Hub, should not be considered a replacement for professional medical advice, diagnosis, or treatment. If you have any health-related inquiries, consult with your preferred healthcare professional or visit a licensed, Canadian physician through Get Gambit for a supported condition.

This article has been medically reviewed by:

Dr. Taneer Ahmed, MBBS, MS



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