Everyone sheds about 50 to 100 hairs each day. As hair goes through its growth cycle, it is completely normal for hair follicles to go through a resting phase and shed hair. However, when excessive hair is shed, it may indicate that your body is under stress and is conserving energy by not supporting hair growth.
While 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.
Hair loss is a concern because it affects self-image, but it does not always indicate a health condition and, in many cases, it may be treatable.
Other than counting the number of hairs that fall or clump in your comb, how can you tell the difference between normal hair shedding and abnormal hair loss or shedding?
Everyone has about 100,000 hair follicles on their head. Of these, about 85% to 90% are in the anagen phase, 1% to 3% in catagen, and 5% to 10% in telogen. If more hair follicles than expected go into the telogen resting phase, you will notice increased hair shedding. This condition is called telogen effluvium. It causes hair to come out in clumps because many hair follicles have prematurely entered the resting phase. Telogen effluvium typically occurs three to five months after the stressor that caused it and is typically self-limiting.1 Anagen effluvium usually affects hair follicles all over the scalp. The onset is more rapid than telogen effluvium, and it can cause widespread hair loss.
Hair loss usually has an underlying physical cause, and until that is resolved, hair loss will typically continue. If you have hair loss, talk to your doctor to see if you have any medical problems or are taking any medications that are associated with hair loss. Hair shedding is a response to a physiological or psychological stressor. It occurs suddenly and resolves when the stressor resolves.
Hair loss occurs when the balance between hairs entering the growth and resting phases is imbalanced.
Potential causes of hair loss in women and men include:
Physiological stress causes telogen effluvium, a condition that causes diffuse hair thinning, so treatment depends on the underlying cause. In most cases, telogen effluvium resolves on its own. However, if you are losing more hair than the expected 50 to 100 per day, here are some potential causes:
Acute illnesses such as COVID-19, severe infections, major surgery, and severe trauma can all trigger hair loss. In March 2020, dermatologists published a paper in the Journal of the American Academy of Dermatology describing a 400% increase in telogen effluvium in New York City’s Hispanic and Latinx populations. This indicates that COVID-19 was especially widespread in these populations. COVID-19 infections present a severe shock to your body, which triggers more hairs to enter a telogen phase followed by shedding.
Hair shedding is not listed among the potential side effects associated with COVID-19. However, the increased number of cases of telogen effluvium after COVID-19 infections suggests that it is a trigger for hair loss. Genetic predisposition and nutritional status are likely to play a role in determining who will experience hair loss after an infection.
Telogen effluvium, or sudden hair shedding, causes hair to come out in clumps. Hair thinning is typically uniform over the scalp. Other than hair loss, the scalp should look completely normal. If this should happen, think back three to five months, and see if you can identify a stressor that may cause excessive hair shedding.1
If you notice patchy areas of hair loss, significant hair loss, inflammation, physical symptoms, scaling, or scalp redness, hair loss is more likely, and a dermatologist can help make an accurate diagnosis and recommend a treatment.
Depending on the cause, you may be able to control some of the triggers for hair shedding:
Treatment options are based on personal preference and the causes of hair loss. If you think a physical condition may be causing your hair loss, see a dermatologist. The earlier conditions such as hypothyroidism, tinea capitis, and alopecia areata are treated, the more successful treatment is likely to be.
If you have hair loss consistent with male or female pattern baldness, ask your doctor about finasteride. Finasteride is a competitive inhibitor of Type II 5α-reductase. This means it inhibits the enzyme Type II 5α-reductase and decreases its ability to convert testosterone to DHT. By blocking Type II 5α-reductase, the conversion of testosterone to DHT is reduced by up to two-thirds. In people with a genetic predisposition, DHT shortens the hair growth phase from years to months. Finasteride can reduce DHT, and restore hair growth and prevent further hair loss.
While we strive to always provide accurate, current, and safe advice in all of our articles and guides, it’s important to stress that they are no substitute for medical advice from a doctor or healthcare provider. You should always consult a practicing professional who can diagnose your specific case. The content we’ve included in this guide is merely meant to be informational and does not constitute medical advice.
1. Phillips TG, Slomiany WP, Allison R. Hair Loss: Common Causes and Treatment. Am Fam Physician. Sep 15 2017;96(6):371-378.
2. Schwartz R. Anagen Effluvium. Medscape. https://emedicine.medscape.com/article/1073488-overview#a7
3. Campbell C, Bahrami S, Owen C. Anagen Effluvium Caused by Thallium Poisoning. JAMA Dermatol. Jun 1 2016;152(6):724-6. doi:10.1001/jamadermatol.2016.0194
4. Rogers NE, Avram MR. Medical treatments for male and female pattern hair loss. J Am Acad Dermatol. Oct 2008;59(4):547-66; quiz 567-8. doi:10.1016/j.jaad.2008.07.001