Dry, brittle hair can be caused by many things, including common hair care products and several general medical conditions. Physicians who will be well qualified to discuss this issue with you include your internal medicine physician or your family medicine doctor
The most common cause of dry, brittle hair is the use of certain harsh chemicals, including those used to bleach, dye, or curl hair. Overwashing your hair, even with a gentle shampoo can remove essential hair mosturizers. Even washing just once a day can be too much for some sensitive hair. Blow driers and curling irons can also be damaging. Over exposure to strong sunlight can also at times be damaging to your hair.
Additionally, there are several medical conditions that can manifest with dry brittle hair. These include hypothyroidism, especially if you also experience fatigue, weight gain and sensitivity to temperature. Similarly, numerous vitamin or mineral deficiencies can cause brittle hair. People who struggle with eating disorders and other forms of malnutrition can also have dry, brittle hair.
As always, the diagnosis and management of your specific condition will require a physical examination by your personal physician. It is recommended that you schedule an appointment with your internal medicine physician or your family medicine doctor.