What Causes Brittle Nails & Thin Hair?

Thin, fragile hair and brittle, breakage-prone nails are often part of the normal aging process. Overdoing cosmetic treatments like chemical hair processes and manicures with artificial nails or dark polish can also damage your hair and nails over time. Less commonly, the combination of thin hair and brittle nails signifies a more serious medical problem, such as thyroid disease, eating disorders or biotin deficiency.


Thin, fragile hair and brittle nails are two of the key signs of hypothyroidism, a condition in which the thyroid gland does not produce a sufficient amount of thyroid hormone. Although brittle, the nails are usually thickened. The hair also tends to be dry. Many other symptoms may occur with hypothyroidism, such as dry skin, weight gain, increased sensitivity to cold, fatigue, depression, paleness, constipation and swelling, especially in the hands and feet and around the eyes. Hair and nail symptoms caused by hypothyroidism typically improve when the disease is treated with thyroid hormone replacement therapy.


Video of the Day

Video of the Day

Eating Disorders

Thin hair and brittle nails can also be the result of eating disorders, especially anorexia nervosa. This medical condition is characterized by an intense fear of gaining weight. People with anorexia nervosa are very thin, as they greatly reduce their caloric intake and often exercise a lot. Consequently, they may not consume sufficient nutrients to maintain strong hair and nail cells. Hair on the head is thin and fragile, and fine hairs may appear on other parts of the body such as the back and arms. As noted in a review article published in "Dermatoendocrinology" in September to October 2009, various other nail changes can occur in addition to brittle nails. These include ingrown toenails, lines running along the length of the nails and redness around the nails, among others. Anorexia often requires a combination of medical and psychological treatments.

Biotin Deficiency

Biotin, also known as vitamin B7 or vitamin H, helps your body metabolize the amino acids it needs to build healthy hair and nails. People with insufficient amounts of biotin may have thin hair, hair loss and brittle, thin nails. They may also develop inflamed eyes, a red rash on the face, depression, fatigue, hallucinations and numbness and tingling in the arms and legs. However, true biotin deficiency is rare because bacteria in the intestines make biotin that is absorbed into the body and biotin is found in a large number of foods, especially egg yolks, sardines, nuts, beans and whole grains. Although biotin supplements are commonly used by people to improve their hair or nails, there is very little scientific evidence indicating that supplements are useful for people with normal biotin levels. Authors of a study published in the April to June 2016 issue of "International Journal of Trichology" concluded that biotin should not be used to treat hair loss unless low biotin levels are proven and other causes have been excluded.


Seeking Medical Attention

See your doctor if you have brittle nails or thin hair, especially if you have both. Although they may be explained by your cosmetic practices or normal aging, the combination of symptoms may be due to significant medical problems that require treatment.

Reviewed and revised by: Mary D. Daley, M.D.




Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.

Report an Issue

screenshot of the current page

Screenshot loading...