Thin, fragile hair and brittle, breakage-prone nails can be early warning signs of a more serious medical problem. Though overdoing cosmetic treatments like chemical hair processes and manicures with artificial nails or dark polish can damage your hair and nails over time, the combination of thinning hair and nails usually stems from a more serious cause.
Thin, fragile hair and fingernails are one of the early signs of hypothyroidism, a condition in which your thyroid gland can't produce its thyroid hormone in sufficient amounts. If you have hypothyroidism, you may notice other symptoms in addition to thinning nails and hair, including fatigue, depression, paleness, unintentional pain or increased sensitivity to cold, according to MedLine Plus, the online health information website maintained by the U.S. National Library of Medicine and the National Institutes of Health. The hair and nail weakness caused by hypothyroidism typically improves when the hypothyroidism is treated.
Thin hair and brittle nails can also be a result of eating disorders such as anorexia nervosa. Anorexia is a medical condition characterized by an intense fear of gaining weight. Because people with anorexia obsess about food and severely limit their nutritional intake, they may not get the nutrients they need to maintain strong hair and nail cells. Anorexia often requires a combination of medical and psychological intervention to treat, according to the U.S. Department of Health and Human Services Office on Women's Health. If anorexia is a long-term issue, the weakness it causes in your hair and nails may be permanent.
Biotin, part of the B vitamin complex, helps your body metabolize the amino acids it needs to build healthy hair and nails. Though serious biotin deficiency is rare, not getting enough biotin in your daily diet can leave your hair and nails thin and brittle, according to the University of Maryland Medical Center. Increasing your biotin intake--through supplements or through biotin-rich foods like egg yolks, sardines, nuts, beans and whole grains--can restore strength and health to hair and nails.