Dry and yellow hair can be caused by frequent perming and coloring of the hair, or it can be caused by malnutrition, hypothyroidism and other diseases. 1. Hair perming and coloring: If the frequency of perming and coloring is too high in life, the chemical agents will cause damage to the hair, and thus dry and yellow hair will appear. 2. Malnutrition: This disease is mainly caused by insufficient or imbalanced intake of nutrients, digestive dysfunction and other reasons. Since the growth of hair is related to the nutrients in the body, when malnutrition occurs, it cannot provide the basic substances for the hair in time, so it will gradually become yellow and dry. Patients may also experience symptoms such as fatigue and loss of subcutaneous fat. 3. Hypothyroidism: The occurrence of this disease is related to thyroid destruction, autoimmune diseases, insufficient iodine intake, pituitary gland diseases, congenital thyroid deficiency and other factors. Because hypothyroidism affects the metabolism of the whole body, some patients will have dry and yellow hair, as well as yellow skin on the hands and feet and thinning hair. There are many causes of dry and yellow hair, so it is recommended that patients go to the hospital to clarify the specific cause.