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What causes sudden hair loss?

yael coopermanlinnea zielinski

Reviewed by Yael Cooperman, MD, written by Linnea Zielinski

Last updated: Mar 24, 2021
6 min read

Hair loss of any type is distressing, but large clumps of hair falling out overnight can be traumatic. 

Many people experience sudden hair loss, which can be the result of thyroid issues, psoriasis, prescription medications, and chemotherapy drugs. Certain types of hair loss are also associated with higher rates of anxiety and depression (Sellami, 2012).

Sudden hair loss is typically a sign of two conditions: telogen effluvium or alopecia areata. Telogen effluvium is commonly caused by stress, which increases the natural rate of hair loss. Alopecia areata is an autoimmune condition that causes your body to attack its hair follicles, resulting in hair loss.

These conditions are different from hereditary hair loss, which generally causes your hairline to recede or thin gradually, as in the case of male and female pattern baldness (Ho, 2020). 

Here’s what you need to know about sudden hair loss, what causes it, and treatment options available for it. 


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What is telogen effluvium and how does it cause hair loss?

Telogen effluvium is a condition that causes sudden, excessive hair loss. Here are some things that commonly trigger this type of hair loss (Hughes, 2020):

  • Severe psychological stress
  • Postpartum hormone changes
  • Major physical trauma like surgery
  • A really bad infection
  • Stopping the use of medications that contain estrogen
  • Nutritional deficiencies like low protein intake or an iron deficiency
  • Hypothyroidism
  • A very low-calorie or “crash” diet

Your body considers all these things stressful, even if you don’t. Whatever the triggering event is, it forces hair to suddenly transition from the growth phase to the resting phase—the phase where hair is normally shed. It’s not the shedding itself, but hairs rapidly leaping from one phase to another that causes sudden shedding.

We all lose hair naturally as follicles cycle through the phases of hair growth. But if your hair loss feels excessive, you could have telogen effluvium or another condition called androgenic alopecia, which is more commonly known as female and male pattern baldness (Rebora, 2019).

telogen effluvium androgenic alopecia normal hair loss
Number of hairs lost >100 with an average of 300 >100 strands per day 50-100 strands per day
Type of hairs lost Long hairs Short, thin hairs Long hairs

If you’re losing short, thin hairs along with longer ones, you may have a combination of telogen effluvium and androgenic alopecia. This is different from alopecia areata, which we’ll dig into below. 

Sudden hair loss from telogen effluvium typically starts three months after a major stressor, but there have been reports of even longer intervals between the stressful event and the start of hair loss (Hughes, 2020).

telogen effluvium androgenic alopecia alopecia areata
Cause Triggering event Genetic Body attacks the hair follicles
When it starts 3 months after the trigger As early as teen years and increases with age Can occur at any age
Treatment Identify and treat the underlying cause. Can resolve on its own, but medication can help regrow hair. Required for hair loss to stop May spontaneously go into remission, but treatments are also available

Getting a diagnosis of telogen effluvium may not feel like good news, but there is a silver lining. If a stressful event has caused your telogen effluvium, it will likely go away on its own after six months (Malkud, 2015). That means your hair may continue to fall out for six months, but how much you lose usually lessens over time (Mysore, 2019).

If a hormonal imbalance or nutritional deficiency is affecting hair loss, it should stop as soon as the underlying issue is corrected. In many cases of hair loss triggered by medications, regrowth starts as soon as the drug is out of your system (Hughes, 2020).

Regrowing your hair to how it was before telogen effluvium can take time. You may start to notice regrowth a few months after the trigger is removed, but complete restoration can take over a year—especially for those with longer hair (Mysore, 2019). 

What is alopecia areata and how does it cause hair loss?

Alopecia areata, also called patchy hair loss, is an autoimmune condition that causes your body to attack its follicles, which results in hair loss. 

Instead of increased hair loss all over, this condition tends to cause round, bald patches that may eventually merge into larger bald spots (Lepe, 2020). Alopecia areata affects roughly 2% of the general population (Pratt, 2017).

Researchers don’t fully understand what triggers alopecia areata, however, studies have found hair loss can be triggered by things like physical or emotional stress, infection, and certain drugs (Gilhar, 2012). 

You’re also at a higher risk of developing this condition if someone in your family has experienced it before. Although it can affect children, alopecia areata usually appears in adults between ages 25 and 36 (Lepe, 2020).

There’s no cure for alopecia areata, but treatments are available to help manage symptoms. In some cases, people may not require treatment at all. 

Roughly half of the people who experience alopecia areata will see hair start to grow back within a year without any treatment at all (Harries, 2010). Keep in mind that relapses are possible, and hair loss can get worse before it gets better. 

A healthcare provider may also recommend other treatments to stop hair loss like corticosteroid shots and topical products, which we’ll get more into below.

How can I regrow any hair I’ve lost? 

You may have heard of minoxidil (brand name Rogaine), which is a topical medication that can help promote hair growth.

It’s available in liquid or foam form in concentrations of 2% and 5%. Researchers suggest minoxidil works by increasing blood flow to affected areas, which delivers more nutrients that encourage new hair growth. This treatment may also shorten the resting phase of hair follicles so they switch to the growth cycle sooner (Badri, 2020).

Higher concentrations of minoxidil are more effective at regrowing hair, but can also cause more side effects, which include itching and irritation at the application site (Badri, 2020).

While 5% minoxidil has been approved by the U.S. Food and Drug Administration (FDA) for use in men, it’s not typically recommended to women as it can cause excessive hair growth. Still, a healthcare provider may decide the benefits outweigh the risks and recommend 5% minoxidil—as long as you’re closely monitored for side effects.

If you have telogen effluvium, products like minoxidil can encourage hair regrowth, but addressing any underlying health conditions or nutrient deficiencies is generally the best solution to the problem (Hughes, 2020). A healthcare professional may suggest a healthy eating plan or supplement regimen if your hair loss is caused by a protein or iron deficiency.

First-line drug treatments are extremely effective for alopecia areata, but they can be harsh. One small study evaluated the use of two medications, methotrexate and corticosteroids, and found that a combination of the two was more effective than methotrexate alone at regrowing hair (Hammerschmidt, 2014). 

If your hair has started falling out suddenly, your best bet is to talk to a healthcare provider. They can help you determine what’s causing the sudden hair loss and correct any underlying issues that may be contributing. 


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.


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Yael Cooperman is a physician and works as a Senior Manager, Medical Content & Education at Ro.