What Causes Hair Loss?

Kristin Hall, FNP

Medically reviewed by Kristin Hall, FNP

Written by Our Editorial Team

Last updated 12/17/2020

Hair loss is a common and frustrating problem that can affect men of all ages. According to the American Hair Loss Association, approximately two thirds of all American men will experience some degree of hair loss by the age of 35.

By the age of 50, approximately 85 percent of American men will have significant hair thinning compared to earlier in their lives. While male pattern baldness is most common in middle-aged and older men, you can start losing hair in your 20s and thirties.

Although male pattern baldness — the most common form of permanent hair loss — can seem like a mystery, the factors that cause hair loss in men are actually thoroughly studied and well understood by the scientific community.

If you’re affected by hair loss, it’s important to understand the cause before you start looking at treatments.

By understanding what causes hair loss, you’ll be in a better position to take action and bring your hair loss to a halt, or even potentially grow back some of your “lost” hair.

Below, we’ve explained the factors that cause hair loss from male pattern baldness. We’ve also briefly discussed other forms of hair loss and their causes.

Finally, we’ve listed science-backed treatments that you can use to stop or reverse your hair loss if you’re affected. 

What Causes Male Pattern Baldness?

Male pattern baldness, or androgenetic alopecia, is a form of hair loss that tends to affect men as they age. It’s characterized by the gradual loss of hair on your scalp, with symptoms usually starting at any time after puberty.

Hair loss from male pattern baldness usually begins with a receding hairline. You might notice that your hairline gradually takes on a “V” or “M” shape. If your hair loss becomes more severe over time, you may lose all of the hair, aside from a horseshoe pattern on the back and sides. 

Male pattern baldness is caused by a combination of genetic factors and your body’s production of male sex hormones, or androgens.

More specifically, hair loss from male pattern baldness is caused by a genetic sensitivity to the hormone dihydrotestosterone, or DHT.

DHT is created by your body as a byproduct of testosterone. As a man, testosterone plays an important role in a huge range of biological processes. It’s important for everything from giving you male genitals before birth to your muscle mass, bone strength and masculine voice.

Your body uses testosterone as a building block for other important hormones.

Similarly, a small amount of your testosterone is converted into DHT by an enzyme called 5 alpha-reductase.

DHT is a critical hormone early in your life. It’s particularly important prior to your birth, when it acts to prevent the development of female characteristics and create your penis, testicles and prostate gland.

It’s also important during childhood and puberty. During your teenage years, DHT and several other hormones are responsible for things like your facial, pubic and body hair growth, as well as the full development of your male physical characteristics.

Put simply, DHT plays a crucial, central role in your physical development during childhood and adolescence.

Unfortunately, DHT also has a range of negative effects, especially if you’re genetically prone to male pattern baldness.

As you enter adulthood, DHT stops playing such a key role in your physiology. Instead, it starts doing two things. The first is slowly enlarging your prostate gland. The second is causing your hair follicles to gradually become weaker and, in some cases, stop producing new hairs.

Your hair follicles contain proteins known as androgen receptors — receptors that are designed to attach to androgens and receive their instructions. 

You can think of these receptors as a sort of biological port, like on an electronic device. When an androgen like testosterone or DHT comes into contact with an androgen receptor, it plugs in and delivers its hormonal information to the surrounding tissue.

Androgen receptors are found all around your body. They’re responsible for a diverse range of biological functions, including the maintenance of your cardiovascular, musculoskeletal, neural, immune, reproductive and hematopoietic systems.

Although all hair follicles contain some androgen receptors, they’re particularly numerous in the hair follicles located in areas of the scalp affected by male pattern baldness.

When DHT binds to the androgen receptors in your hair follicles, it causes them to miniaturize. Over time, the follicles stop producing new hairs, creating the classic V, M or U-shaped hairline that’s typically associated with hair loss in men.

The effects of DHT aren’t immediate — if you’re prone, you probably won’t wake up one morning with severe hair loss. However, over time, DHT can take a serious toll on your hair if you have a genetic predisposition to male pattern baldness. 

We’ve talked about this process in greater detail in our complete guide to DHT and its effects on male hair loss

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How to Treat Male Pattern Baldness

Several treatments are available for male pattern baldness, including two medications approved by the FDA.

Most treatments for male pattern baldness work by either blocking DHT in the body or in the scalp specifically, or by stimulating the growth of new hairs. 


Finasteride, a medication that’s FDA-approved for treating hair loss, is one option for blocking DHT. It works by inhibiting the effects of 5 alpha-reductase, the enzyme that’s responsible for converting testosterone into DHT.

In a 1999 study, researchers found that a 1 mg daily dosage of finasteride (the regular dosage prescribed for hair loss) reduces DHT levels in the scalp by 64.1 percent.

Other research has found that finasteride has positive effects on hair loss and hair regrowth for men with male pattern baldness.

For example, clinical trials of finasteride found that 83 percent of men with hair loss experienced no further hair loss after using finasteride for two years.

Furthermore, 66 percent of men with hair loss showed an improvement in hair growth after two years of treatment with finasteride.

We offer finasteride online, following an online consultation with a healthcare provider who will determine if a prescription is appropriate. You can learn more about finasteride in our guides to finasteride results and finasteride side effects


Minoxidil is a topical medication that stimulates hair growth. Although its precise mechanism of action isn’t well known, research shows that it causes hair to enter into the growth phase of its cycle early, increasing the number of hairs that are growing at any one time.

Unlike finasteride, minoxidil doesn’t block the effects of 5 alpha-reductase or reduce your DHT levels. However, research shows that it can improve hair growth and make the effects of male pattern baldness less severe.

For example, a study involving more than 390 men published in 2002 found that treatment with two percent and five percent minoxidil solutions increased hair count in men with male pattern baldness over 48 weeks. Of the two medications, the stronger five percent minoxidil solution was the most effective. 

A larger-scale study from 2004 came to a similar conclusion, with 84.3 percent of the men who took part in the study rating minoxidil as “very effective,” “effective” or “moderately effective” at promoting hair regrowth after 12 months.

We offer minoxidil online. You can learn more about how this medication works, its side effects and more in our guides to how long minoxidil takes to start working and its most common side effects

Other Types of Hair Loss and Their Causes

For men, male pattern baldness is the most common type of hair loss, meaning it’s usually the culprit if you’ve noticed thinning or a receding hairline. 

However, several other forms of hair loss can also potentially take their toll on your scalp and hairline. We’ve listed several of these below, along with information on why each form of hair loss occurs and how it can be treated.

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Alopecia Areata

Alopecia areata is an immune system disease that causes hair loss. Although the exact cause isn’t well understood, experts believe that factors such as changes to certain genes in the hair and skin may cause it to develop.

Treatments for alopecia areata include topical and injectable corticosteroids, topical anthralin and minoxidil.

Anagen Effluvium

Anagen effluvium is a form of hair loss in which hairs fall out during the anagen phase of their growth cycle due to a toxic or inflammatory response. It’s often associated with severe malnutrition, radiation and certain medications, including chemotherapy.

Although no treatments have proven effective at stopping or preventing anagen effluvium hair loss, medications like minoxidil may help to limit the period of balding.

Telogen Effluvium

Telogen effluvium is a form of hair loss that occurs after a stressful or traumatic event. This kind of hair loss is often caused by illnesses, metabolic stress, trauma, infection, surgery, hormonal changes, nutritional deficiencies and use of certain medications.

After the cause of hair loss has been identified and treated, telogen effluvium generally doesn’t require further treatment.

Tinea Capitis

Tinea capitis, or scalp ringworm, is a fungal infection that affects the scalp. When the fungi that cause the infection penetrate the root sheath of the hair follicle, they may cause temporary hair loss. In some cases, tinea capitis can cause irreversible damage due to scarring.

As a fungal infection, tinea capitis is usually treated with antifungal medications. It’s important to treat this infection early, as it can spread quickly across the scalp and cause permanent hair loss if left untreated.

Cicatricial Alopecia

Cicatricial alopecia, or scarring alopecia, is an uncommon group of hair loss disorders in which the hair follicles are permanently damaged. In people with cicatricial alopecia, hair follicles are replaced by fibrous tissue, preventing new hairs from growing. 

The cause of cicatricial alopecia isn’t currently known. Treatment typically involves the use of topical steroids, retinoids, antibiotics, hydroxychloroquine and other medications, with a variety of treatments used depending on the specific type of cicatricial alopecia hair loss.

However, even with treatment, the goal isn’t to stop scarring alopecia, but rather reducing the symptoms and slowly the progression of the disease. 

Traction Alopecia

Traction alopecia is a type of hair loss that often occurs in people with hairstyles that pull on the roots of the hair. It’s generally caused by hair care, with hairstyles that put repetitive tension on the hair the most common reason for this type of hair loss.


Trichotillomania is an impulse control disorder in which a person feels the urge to pull out their own hair. It often starts during childhood or adolescence and can cause noticeable hair loss in certain parts of the scalp.

Although there are no well established treatments for trichotillomania, symptoms may improve with cognitive and/or behavioral therapy, hypnosis or the use of medication.

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In Conclusion

In men, the most common cause of hair loss is male pattern baldness. This type of hair loss is caused by a combination of genetic and hormonal factors, with dihydrotestosterone (DHT) the main culprit.

If you’re prone to male pattern baldness, several treatments are available, including finasteride and minoxidil. Both of these medications are approved by the FDA and have shown real results in clinical trials and scientific studies. 

If you’re losing your hair and don’t think that male pattern baldness is the cause, it’s best to talk to your healthcare provider. They’ll be able to diagnose the cause of your hair loss and suggest a safe, effective form of treatment.

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.