The 10 Most Common Causes Of Hair Loss

March 25, 2024
A woman with hair loss

Alopecia, or hair loss, can be localized or diffuse, reversible or permanent, limited to the scalp or widespread, and caused by scarring or not. Everyone sheds 50 to 100 hairs daily, but as you lose more, patchy areas on the scalp or hair thinning becomes more obvious. Alopecia has several subtypes according to the various causes. In this guide, we will consider the top 10 most common hair loss causes.


The three phases of hair growth are the same for everyone: anagen (growth phase), catagen (transition phase), and telogen (rest phase). The length of these phases and the percentage of hairs in each phase vary throughout your lifetime. Anagen typically lasts for about three years, catagen lasts only a few days, and telogen lasts for about three months. As we age, the anagen growth phase gets shorter, estrogen and testosterone levels decline, and hair follicle size diminishes. By the age of 50, half of all men have experienced hair loss. This number increases to 70% with advanced age. Hair loss and graying tend to both increase with age.

Senescent alopecia (hair loss associated with aging) is closely linked to male pattern hair loss (MPHL) and female pattern hair loss (FPHL). Smoking, exposure to ultraviolet light, and poor nutrition can also increase hair loss.1

Treatment options vary by cause:

  • When hair loss is because of changes in hormone levels, minoxidil or finasteride reduces or even reverses hair loss.
  • Wearing a hat and using sunscreen protects hair follicles from the effects of UV light.
  • Quitting smoking improves blood flow to the hair follicles and reduces inflammation.
  • Consuming a diet high in whole foods and antioxidants provides hair follicles with the nutrients it needs for hair growth.
  • Age management supplements can reduce oxidative stress and protect skin and hair from further damage.
woman with thinning hair

Autoimmune Disease

Alopecia areata is an autoimmune cause of alopecia that affects as many as 6.8 million people in the United States, with an individual lifetime risk of developing it set at 2.1%.2 Alopecia areata typically causes patchy hair loss. Unlike other conditions that cause hair loss, the onset of alopecia areata may be very dramatic. Most causes of alopecia areata resolve spontaneously, but up to one-fourth are more severe and may persist.2

The immune system is a complex system of cells, hormones, and signaling chemicals that protect your body from pathogens. Sometimes, your immune system inadvertently attacks your own body tissues and organs. This causes the many autoimmune diseases. Immunosuppressant Drugs are used to reduce the effect of the rogue attack on your body cells. Read more about Immunosuppressant drugs: Common Medications and Tips for Boosting Your Immune System.

Treatment options for alopecia areata include:2,3

  • Intralesional steroid injections reduce inflammation.
  • Systemic steroids suppress the effects of the immune system on the hair follicle.
  • Topical immunotherapy provides a more directed approach. It triggers a localized mild contact dermatitis and stimulates the immune system.
  • Olumiant is a recently approved treatment for alopecia areata. It is a Janus kinase (JAK) inhibitor. It blocks an enzyme that is found in the pathway that leads to hair-follicle inflammation.

While you can’t “boost” the immune system, you can provide your body with the nutrients and antioxidants it needs to protect your body. Read more in the Ultimate Guide to Immune Health.

Chemotherapy And Radiation

Chemotherapy targets rapidly dividing cells. These medications are used to stop the growth of rapidly dividing cancer cells, but they also halt the growth of other rapidly dividing cells, such as hair follicles and the lining of the intestines. Not all chemotherapy medications cause hair loss. Regrown hair may vary in color or structure, but these changes are likely temporary.4

Cooling caps that reduce blood flow to the scalp may reduce chemotherapy-induced alopecia. They work by decreasing the amount of chemotherapy delivered to the scalp.5 Minoxidil may help with hair regrowth after chemotherapy.6

Radiation therapy targets cancers that are rapidly growing to shrink them. Depending on the treatment area, hair loss is possible, especially when treating head and neck cancers. Hair regrowth may restart a few weeks after treatment, but hair loss may be permanent.

woman with baldness from chemotehrapy

Damaging Hair Styles

Hairstyles that put excessive tension on the hair follicles can cause localized hair loss. This is called traction alopecia. Tight ponytails, braids, dreadlocks, and other styles can cause it.

Treatment involves preventing hair loss by:7

  • Using looser hairstyles
  • Varying hairstyles
  • Avoiding the use of chemical relaxants
  • Avoiding overuse of dry shampoos


Male pattern hair loss (MPHL) and female pattern hair loss (FPHL) are the most common forms of hair loss. Prevalence rates range from 16% to 98% depending on the age group and whether mild forms of hair loss are included, 16% of 18 to 29-year-olds have significant hair loss8, and 98% of 50-year-old men have at least frontal recession (receding hairline at the forehead).9 Overall, more than half the adult U.S. population is affected by hair loss.10 MPHL and FPHL, formally called androgenic alopecia, effect 50 million men and 30 million women in the U.S.

MPHL and FPHL are treatable and reversible forms of hair loss. Their cause is thought to be a genetic hair follicle sensitivity to dihydrotestosterone (DHT), a hormone that causes miniaturization of hair follicles.

Testosterone and DHT are androgens that play an important role in developing male sexual characteristics before birth and adolescence. An enzyme, 5α-reductase, converts up to 10% of testosterone to DHT in adults. DHT is a stronger, more powerful androgen than testosterone.

Treatment options:6

  • Finasteride: a competitive inhibitor for type II 5α-reductase
  • Topical minoxidil
  • Saw palmetto
  • Green tea extract

Hormonal Imbalances

Hormonal imbalances occur throughout your lifetime and may indicate medical conditions such as polycystic ovary syndrome or thyroid disease or result from changing hormone levels from stopping oral contraceptives or pregnancy. Changing hormone levels can cause hair loss. The hair cycle and hair follicle structure are both affected by hormones.

Polycystic ovary syndrome is a common endocrine disorder that affects between 6% and 12% of women.11 It is characterized by having irregular menstrual cycles, excessive hair growth on the face, chest, abdomen, and upper thighs, severe acne, and patches of thickened, velvety, darkened skin called acanthosis nigricans. While excessive hair growth is more common, increased androgens in genetically susceptible people can cause hair loss.12

The thyroid gland, located on the front of your neck, secretes triiodothyronine (T3) and thyroxine (T4). These hormones regulate growth and metabolism. You may notice dry skin and hair when your thyroid gland is underactive. This condition, called hypothyroidism, can cause thinning hair that falls out more quickly.12

After menopause, estrogen levels plummet. Estrogen increases the time a hair follicle spends in anagen, the growing phase. Decreased estrogen causes hair thinning. Progesterone reduces the conversion from testosterone to DHT. In genetically susceptible people, increased DHT increases MPHL and FPHL.

Hormonal imbalances and diabetes in men are connected. Low testosterone is associated with obesity and a higher risk of type 2 diabetes. Spiking blood glucose levels, which are common in diabetes, can reduce the flow of oxygen and nutrients to your hair follicles. Thyroid disease, alopecia areata, and type 1 diabetes mellitus are all autoimmune disorders that more commonly occur together.

If hormonal imbalances are causing your hair loss, then the most important next step is to get an accurate diagnosis and treatment for the underlying cause. In the meantime, here are 7 ways to naturally regulate your hormones.


Some medications can cause hair loss. Medications that have hair loss as a side effect include:

  • Chemotherapy agents
  • Anticoagulants
  • Anticonvulsants
  • Cardiovascular drugs
  • Antimicrobials
  • Antithyroid medications
  • Gout treatment
  • Interferons
  • Cholesterol-lowering medications
  • Psychotropics
  • Retinoids

If you are taking a medication that causes hair loss, ask your doctor if another medication, without this side effect, could treat your condition.


Progesterone increases during pregnancy, and many women notice that their hair is thicker and denser while pregnant. But, after delivery, a major stress on the body, hair loss is common. Two to four months after delivery, many pregnant people experience telogen effluvium. This occurs when large numbers of hair follicles enter the resting phase at once, and hair is shed. Telogen effluvium after delivery commonly lasts 6 to 24 weeks, but rarely it can last as long as 15 months.12

Hair loss after delivery typically resolves on its own. If it persists, see your doctor to see if you have developed any hormonal imbalances that may explain your hair loss. Your doctor may prescribe medical treatment for hair loss after delivery, though it is not safe to use while pregnant.

pregnant woman

Scalp Infections 

Scalp infections, such as the fungal infection tinea capitis, can cause localized hair loss. The exposed scalp will look red, flaky, and itchy and may have visible sores. You may see black dots from broken hairs on the scalp. Antifungal medications treat tinea capita. Once the infection is gone, hair regrows.


Psychological or physical stress can also cause telogen effluvium. This causes an abnormal increase in the number of hair follicles shifting to the telogen rest phase. Hair loss generally starts about three months after the stress trigger that caused it. It takes this long for the hair follicle cycle to finish and release the hair. Telogen effluvium causes hair shedding in a diffuse pattern. If you have patchy or more complete hair loss, alopecia areata or FPHL may be the cause. Hair loss should be temporary, and hair density should slowly return to pre-stress levels.

Excess cortisol, a stress hormone, can also reduce the synthesis of and cause the premature degradation of hyaluronans and proteoglycans, which can damage the health of hair follicles.12

Stress has many effects on your body, especially on your cognitive health. Learn stress management strategies to prevent stress-induced hair loss. Read 7 tips to reduce anxiety and manage stress.

The 10 Most Common Causes Of Hair Loss
Author: Leann Poston, M.D.
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