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Hormonal influences on hair

Factors that influence hair loss

The thyroid is a small gland that resides on the front of your neck. It controls how your body makes proteins and burns energy; it also regulates your metabolism through production of thyroid hormone. Diseases of the thyroid gland can affect hair growth, which fortunately is non-scarring.

Diseases of the thyroid gland

When the thyroid gland produces either too much or too little thyroid hormone, it can have negative consequences for your hair. Fortunately, the following thyroid gland diseases can be detected with a simple blood test:

Hyperthyroidism: When the body produces too much thyroid hormone, you may develop hyperthyroidism. Symptoms of hyperthyroidism include a rapid heartbeat, weight loss, heat intolerance, and nervousness. In addition, your hair becomes extremely thin and sparse.

Hypothyroidism: When the body produces too little thyroid hormone, you may develop hypothyroidism. Symptoms of hypothyroidism include fatigue, cold intolerance, lack of energy, puffiness of the face, and dry skin. In addition, your hair becomes dry, brittle, coarse, and sparse.

The most common cause of hyperthyroidism in the U.S. is Grave’s disease, an autoimmune disease (see the earlier sidebar “What’s an autoimmune disease?”). The most common cause of hypothyroidism in the U.S. is Hashimoto’s thyroiditis, also an autoimmune disease. In developing countries, lack of iodine in the diet is the most common cause of hypothyroidism. However, this cause is rare in the United States because iodine is added to table salt.

How thyroid conditions affect hair growth

Doctors aren’t sure why patients with thyroid disease lose their hair. It could be because the thyroid hormone affects the body’s metabolism, including the hair follicles, and so problems with the hormone cause hair regrowth to slow and hair to become thinner and possibly more brittle. This may result in loss of hair bulk. And if the hair shaft hasn’t fully developed, the ends of the hair may split.

Whether or not the thyroid hormone has a direct effect on the condition of hair and its growth, acute thyroid disease is very stressful. Stress can be an important factor in developing telogen effluvium, in which hair rapidly falls out after prematurely entering the resting phase of the hair growth cycle.

Medications given to treat thyroid dysfunction also can cause hair loss. For example, hair loss is a potential side effect of propylthiouracil, the most common medicine used to treat hyperthyroidism. Synthroid (levothyroxine), the most common drug used to replace thyroid hormone, also may cause hair loss. It’s not known why these medications cause hair loss, but it’s important for patients to be aware of their potential side effects.

Living with a thyroid condition and hair loss

If you suffer from thyroid disease and experience hair loss, you should see two important specialists: the endocrinologist, who can diagnosis and treat your thyroid condition; and the dermatologist, who can figure out the exact cause of your hair loss and determine if it’s related to a thyroid disease. Hair loss can accompany many different conditions, so it’s important to eliminate all other possible causes before assuming that a condition is thyroid related.