One way in which diabetes can cause hair loss is a result of the effects of high blood sugar on the circulatory system. Diabetics typically have higher than normal blood sugar levels. High blood sugar can chemically react with red blood cells, creating a product known as glycosylated hemoglobin. Hemoglobin is an important protein in red blood cells and this modified version causes red blood cells to be misshapen. These misshapen red blood cells are not as flexible and can get stuck when trying to enter small blood vessels (called capillaries), leading to circulation problems. If this occurs in the capillaries that supply blood to the hair follicles, these follicles may die, leading to hair loss.
Another way in which diabetes can cause hair loss is by disrupting the endocrine system. The endocrine system is comprised of many hormones that control different tissues in the body. For example, the endocrine system secretes androgens, which govern hair growth and the health of hair follicles. Uncontrolled diabetes (and the resulting high blood sugar) causes the endocrine system to become disrupted. This can lead to androgen abnormalities, which can cause the hair follicles to go dormant. As a result, the shafts of the hair fall out, which can lead to widespread hair loss. Fortunately, if the diabetes is controlled (through diet and medication), the hormone levels can become stabilized, allowing the hair to grow back.
Diabetes can also have an indirect effect on hair loss as a result of autoimmune disorders. Autoimmune disorders occur when the immune system accidentally attacks healthy tissue because it misidentifies the tissue as foreign. This can be one cause of diabetes, because the immune system can attack insulin-producing cells in the pancreas, leading to reduced insulin production. Alopecia areata is another autoimmune disorder in which the immune system attacks the hair follicles, leading to hair loss and balding. People with one autoimmune disorder (such as diabetes) are more likely to have other problems with their immune system. As a result, people with a history of diabetes are more likely to develop alopecia areata.