The Most Common Causes of Hair Loss, Explained

Google "hair loss" and you'll be met with 1.4 million results. That's the internet's way of telling you that you're far from alone: Almost 50 percent of women and 80 percent of men experience "significant" hair loss over the course of their lives, according to NYU Langone. The causes of hair loss in women are many and complex (even your super high, Ariana Grande-style ponytail could be a contributor). But in most cases, if you're losing hair, you often need to seek medical guidance and tackle the, well, root of the problem.

Before you panic about how much hair you're losing, be aware that it's perfectly normal to lose between 80 and 100 strands of hair every day, says dermatologist Yoram Harth, M.D., founder of MDHair, which offers medical-grade hair loss treatment.

"We have, on average, 100,000 hair follicles," he says. "About 80 to 90 percent of our hair is growing at any given time, and 10 to 15 percent is in a resting phase and will ultimately fall out and be replaced by new hair," notes Dr. Harth. So if you're just feeling mildly alarmed at the quantity of hair coming off when you brush it, you might not have alopecia (the medical term for hair loss); it could just be run-of-the-mill shedding. That said, when the rate of shedding outpaces the rate of growth, then that's considered alopecia, according to NYU Langone.

Of course, it will likely be hard to tell if you're suffering from alopecia — and which specific type of alopecia you're dealing with — without the help of a medical professional. So if you do suspect you're losing more than your daily, 100-hair quota, make sure to book an appointment with your primary care provider, a trichologist (someone who specializes in scalp/hair health), or a dermatologist.

As you've probably noticed by now, hair loss is a complicated subject (understatement of the century). And thus, it bears repeating that a health care professional will be your golden ticket when it comes to diagnosing and treating the type of alopecia that's plaguing you.

Generally speaking, however, it's always, always better to address the root cause of hair loss than to slap a Band-Aid on the problem with creams and gels that haven't been approved by the Food and Drug Administration and medical professionals, says Dr. Harth. "There is no one magic bullet for treating hair loss," he says. (Once you see a doc, these are the best hair growth serums to try.)

Below, Dr. Harth and trichologist and hair loss expert William Gaunitz, W.T.S., explain the most common causes of hair loss in women, as well as symptoms and potential treatment plans to get you started.

The Most Common Causes of Hair Loss — and What to Do About Them

Hereditary or Androgenetic Hair Loss

"The most common cause of hair loss is hereditary hair loss that progresses with age," says Dr. Harth. "In this type of hair loss, the male hormones — [which exist] in both men and women — cause the hair in some areas of the scalp to be smaller, thinner, and later invisible (baldness)."

An estimated 30 million women in the U.S. are affected by androgenetic hair loss, and this particular type of alopecia has a pretty dead giveaway: "Genetic male and female pattern hair loss happens only on the top of the head," says Gaunitz. In this case, Dihydrotestosterone (DHT), a hormone made from testosterone, interacts with the hair follicle receptors to create inflammation, causing the hair to grow thinner as time goes on.

Interestingly, hair loss related to polycystic ovary syndrome and menopause is a type of androgenetic hair loss because these conditions manipulate DHT levels, causing you to lose hair, according to Gaunitz.

Your treatment plan will be as individual as you are, but broadly speaking, androgenetic hair loss treatments usually involve reducing the impact DHT has on the hair follicle. "That could be a topical that reduces DHT or a nutritional supplement that reduces DHT," says Gaunitz. Finasteride is the only FDA-approved pharmaceutical for mitigating the effects of genetic hair loss by blocking the conversion of testosterone to DHT. Because the pharmaceutical route is directly affecting your body's testosterone, it may present more side effects than other interventions — so you can ask your doctor to walk you through the ins and outs of each option.

Nutritional Deficiencies

Gaunitz personally coined the term "nutritional alopecia," and he considers it one of the most prevalent causes of hair loss. "What people don't understand is that just like a plant needs sunlight and fertilizer and water, your hair requires a certain volume of free [bioavailable] nutrition in your blood," he explains. For example, your hair follicles need vitamin D3 as a hormone, zinc, folate, B12, and ferritin (the protein your body uses to store iron).

"These things have to be bioavailable in your blood, so that these little tiny receptor sites — which are kind of like roots that are dangling their receptors into your bloodstream — are absorbing the nutrients to grow the fullest, thickest hair," adds Gaunitz. If you're not getting these essential nutrients, your body will stop growing your hair at a normal rate so it can use that nutrition elsewhere, says Gaunitz. (

To see if you might be dealing with nutritional alopecia, talk to your doctor about getting a blood work panel to see if your vitamin D3 and iron levels are sufficient (this will mean something different for everyone, so you really need to work with a medical professional here), recommends Gaunitz.

Endocrine Disorders

Endocrine disorders, such as hypothyroidism (a disorder where your thyroid doesn't produce enough of your body's crucial hormones), can cause diffuse hair loss, a type of hair loss where you lose hair or experience thinning across the scalp. Hyperthyroidism, or an overactive thyroid, can cause similar issues. The most common cause of hyperthyroidism is Graves' disease, an autoimmune disorder; meanwhile, Hashimoto's thyroiditis (another autoimmune disease) is the most common cause of hypothyroidism.

Other symptoms that you might experience from endocrine disorders include mood swings, fatigue, weakness, unintended weight fluctuations, changes in blood sugar or cholesterol levels, according to Tampa General Hospital.

If you think this might be you, go ahead and see a doc. If your alopecia is stemming from hypothyroidism, it's best to work closely with an endocrinologist who can, for example, prescribe you levothyroxine which is commonly used to treat hypothyroidism.

Extreme Stress

Telogen effluvium is characterized as "sudden" hair thinning that happens due to different types of physical or emotional strife, according to Dr. Harth. "Telogen effluvium can be triggered by a stressful life event, diseases like COVID-19, crash diets, and pregnancy," says Dr. Harth. To be clear, any type of stress — whether it's emotional or physical — can trigger hair loss. You may not experience hair loss immediately, as it could happen within a few months after a stressful "event," according to Mayo Clinic.You may be experiencing telogen effluvium if you're going through a period of extreme stress and noticing that your hair is generally thinning.

Luckily, this type of hair loss is almost always temporary. "The hair will usually regain its thickness in six to nine months," says Dr. Harth.

Chemotherapy

Anagen effluvium is a type of hair loss that happens all over the body, and is a side effect of chemotherapy: a drug treatment that kills rapidly dividing cells, including cancer cells. "Cancer is a rapidly dividing cell and the hair follicle is a rapidly dividing cell. So that's why chemo attacks your hair follicle," explains Gaunitz. If you're undergoing chemotherapy, your hair will start to grow back in about three months after finishing chemo, reaching about four to six inches long in a year's time, says Dr. Harth.

Autoimmune Diseases

Certain autoimmune conditions can cause hair loss — namely lupus erythematosus and alopecia areata, which can cause diffuse hair loss or round bald spots on the scalp, respectively, says Dr. Harth.

Lupus erythematosus, also known as systemic lupus erythematosus, is the most common type of lupus in which the immune system attacks its own tissues, causing widespread inflammation and tissue damage. It can have other symptoms such as fatigue, skin rashes, fevers, and pain or swelling in the joints, and can also show up in "flares," according to the Centers for Disease Control and Prevention.

Alopecia areata is a disease in which the body attacks its own hair follicles, causing hair loss anywhere on the body, according to the American Academy of Dermatology. If you have alopecia areata, you may experience unpredictable cycles of hair loss ans regrowth.

Because both of these diseases are difficult to diagnose, you'll definitely need to see a doctor to determine if this is the cause of your hair loss, and what you can do about it.

Scalp Infections and Diseases

There are a number of other skin and scalp diseases — including psoriasis — that can cause temporary hair loss along the scalp. Infectious diseases of the scalp such as ringworm and shingles can also cause hair loss, according to Dr. Harth. Ringworm in particular causes scaly, red, itchy areas that, left untreated, can lead to permanent bald spots on the scalp, according to Dr. Harth.

If you think you're dealing with an infection or an underlying scalp disease, seek medical treatment as soon as you can to start working one on one with a professional to create a treatment plan.

Traction Alopecia

"A common cause of baldness on the frontal hairline is caused by tight hairstyles like ponytails, braids, and wearing hair extensions," says Dr. Harth. The medical name for this is traction alopecia. (And just like that: full circle back to that Ariana Grande ponytail.)

Luckily, the fix for this one's simple: Try to ease off on tight hairstyles and take it easy on your hair during those burpees. If you catch traction alopecia early, it is reversible and your hair should grow back in a few months, according to the University of Iowa Health Care. If not, you should seek further treatment from a derm or trichologist who can advise on treatment options.