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Thyroid Problems

Problems with your thyroid gland can lead to hair loss.

“Hypothyroidism -- too little hormone -- may cause a host of symptoms, and hair, nails, and skin may become more brittle and break more easily," says Mirmirani. "With hyperthyroidism -- too much hormone -- hair loss can appear as metabolism speeds up.”

Blood tests can confirm whether you have a thyroid problem. Thyroid hormone medication may return your hormone levels to normal and help with hair loss and other symptoms. Your doctor will check every 6 weeks or so to see if you need to change your dosage.

Underlying Scalp Conditions

Hair loss can be caused by a fungus, psoriasis, or dandruff (seborrheic dermatitis).

  • The most common fungal infection affecting the hair is ringworm -- the same thing as athlete's foot. It requires an antifungal medication.
  • Seborrheic dermatitis makes your scalp shed, resulting in greasy, yellowish scales in the hair. Causes include hormonal changes or excess oil in the skin. It can be reversed. Treatment is usually a medicated anti-dandruff shampoo, a prescription antifungal cleanser, or steroid cream. 
  • Psoriasis, an autoimmune condition, produces thick white scale on the scalp that can bleed if pulled off. Treatments include steroid creams, salicylic acid, coal tar, anti-inflammatory drugs, and biologics that suppress your immune system. 

If you think you may have one of these conditions, talk to your doctor.

Skin Disease

Alopecia areata is an autoimmune skin disease that causes hair loss on the scalp and body. It affects about 6.5 million people in the United States. It usually starts with one or more small, smooth circular patches on the scalp. It can progress to total hair loss. 

Hair can grow back in or fall out again at any time; alopecia areata affects each person differently. The underlying cause isn't known yet, Mirmirani says. Genetics may make you more likely to develop it when activated by triggers like stress or illness.

Treatment usually involves injections of corticosteroids and medications that irritate the scalp and cause hair growth to restart.