8 Illnesses That Cause Hair Loss

Vicky Davis

Medically reviewed by Vicky Davis, FNP

Written by Our Editorial Team

Last updated 2/19/2021

The reason you’re going bald might be deeper than you realize. While some hair loss is genetic, a variety of medical conditions can also cause you to lose your hair. Here’s what you need to know and what you can do about it. 

Illnesses That Can Cause Hair Loss

Androgenetic alopecia

Androgenetic alopecia (AGA) is a common form of hair loss in men. This condition is also known as male-pattern baldness.

Hair is lost in a well-defined pattern, beginning above both temples. Over time, the hairline recedes to form a characteristic "M" shape. Hair also thins at the crown (near the top of the head), often progressing to partial or complete baldness.

This type of baldness responds well to medications like minoxidil (a topical treatment) and finasteride (an oral medication). 

Minoxidil works by creating an ideal growth environment for your existing hair follicles. It begins working right away but may take a few months to start to begin seeing results.

Finasteride is a prescription medication that prevents male pattern baldness on a hormonal level. It works by inhibiting the production of 5α-Reductase, the enzyme that converts testosterone into DHT within your body.

Alopecia areata

Alopecia areata is another common disorder that causes hair loss. "Alopecia" is a term that means baldness, and "areata" refers to the patchy nature of the hair loss that is typically seen with this condition.

In most people with alopecia areata, hair falls out in small, round patches, leaving coin-sized areas of bare skin. This patchy hair loss occurs most often on the scalp but can affect other parts of the body as well. 

Less commonly, hair loss involves the entire scalp. This condition is known as alopecia totalis. Other rare forms of alopecia areata, which have different patterns of hair loss, have also been reported.

If you just received your diagnosis and have had alopecia areata for less than a year, your dermatologist may decide to wait it out. Your hair may regrow on its own, making treatment unnecessary.

If you’re had it for more than a year, treatment for alopecia areata includes prescription-strength corticosteroids (either topical or injected), minoxidil and methotrexate.

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Nutritional deficiencies

Iron deficiency is the world’s most common nutritional deficiency and is a well-known cause of hair loss. The degree of iron deficiency that may contribute to hair loss, however, remains unclear.

Zinc deficiency may be either inherited or acquired and may affect multiple bodily systems—including hair growth. A study of 312 patients with androgenetic alopecia showed that they had statistically lower zinc concentrations as compared to 30 healthy controls.

Deficiencies in other minerals and essential vitamins, including niacin, fatty acids, selenium, vitamins D, A and E, folic acid, biotin, amino acids, proteins and antioxidants may cause hair loss as well. 

Treatment for hair loss caused by nutritional deficiencies requires correcting the deficiencies. What is unclear is the ideal range of micronutrient levels to prevent or correct hair loss. 

In iron deficiency and anemia, supplementation is required, but patients with iron deficiency in the absence of anemia must be approached on a case-by-case basis.

It is believed that raising levels of storage iron may improve hair loss, although the research is not conclusive.

Most importantly, if you are receiving iron supplementation, your healthcare provider must monitor you due to toxicity risk.

For other nutrient deficiencies, such as zinc, supplementation has resulted in hair growth, although, again, your healthcare provider should monitor your intake to mitigate your toxicity risk.

Fungal infections

Trichomycoses, by definition, are diseases of the hair caused by fungi. Human trichomycosis causes the loss of hair. Fungal infections can include dandruff (pityriasis capitis simplex), tinea capitis and others.

Treatment for fungal infections of the scalp includes prescription shampoos, topical antifungal medications and oral medication. 

Autoimmune disorders

Hair loss is a symptom of several autoimmune disorders, including hypothyroidism and lupus.

Hypothyroidism, also called underactive thyroid, is when the thyroid gland doesn’t make enough thyroid hormones to meet the body’s needs.

Thyroid hormones control the way the body uses energy. Without enough thyroid hormones, many of your body’s functions slow down—including hair growth.

Treatment for hair loss caused by hypothyroidism is typically oral thyroid replacement medication. Once your thyroid levels are back to a normal level, your hair should begin to grow back.

A lupus diagnosis often brings many physical changes, including hair loss. Whether or not hair grows back on the scalp depends on whether there is scarring, as well as how much scarring there might be. When the hair loss is widespread, but there is no scarring, the hair will often grow back. 

If hair loss is caused by medication, you may have to wait until your lupus is under control to treat the hair loss. This type is mostly reversible.

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Does cancer cause hair loss? No, cancer does not typically cause hair loss. However, some types of cancer treatment, including chemotherapy, can cause the hair on your head and other parts of your body to fall out. Radiation therapy can also cause hair loss on the part of the body that is being treated.

Once chemotherapy and radiation therapy have stopped, your hair will likely begin to grow back. 

Hair often grows back in two to three months after chemotherapy treatment has ended. 

After radiation therapy, hair likely grows back in three to six months. If you received a very high dose of radiation, your hair may grow back thinner or not at all on the part of your body that received radiation.


The hair follicle is a highly active organ and needs a special environment with an adequate supply of oxygen and nutrients. 

Type 2 diabetes causes a chronic decrease in the oxygen and nutrient supply, which can cause follicular damage. This results in hair alterations like hair thinning, hair fragility, sparseness of hair or decreased hair growth speed.

Early diagnosis and treatment are key to getting your diabetes under control. This will also aid in preventing further hair loss from the disease. To learn more, you can read our article on Diabetes and Hair Loss.


Trichotillomania is a body-focused repetitive behavior classified as an impulse control disorder that involves pulling out one's hair. Hair pulling may occur in any region of the body in which hair grows, but the most common sites are the scalp, eyebrows and eyelids.

The two methods of treatment that have been scientifically researched and found to be effective are behavioral therapy and medications, which are generally used in combination.

Behavioral therapy helps people learn a structured method of keeping track of the symptoms and associated behaviors, increasing awareness of pulling, substituting incompatible behaviors and several other techniques aimed at reversing the “habit” of pulling.

Medications help some people temporarily, but symptoms are likely to return when the medication is stopped unless behavioral therapy is incorporated into treatment.

Medications may help to reduce the depression and any obsessive-compulsive symptoms the person may be experiencing.

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From nutritional deficiencies to hypothyroidism and diabetes, there are many medical conditions that can cause hair loss.

That’s why it’s important to keep a close eye on your health to spot any changes that may occur. If you’ve been noticing hair loss for any reason, talk to your healthcare provider about potential underlying causes or conditions.

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.