Hair thinning on both sides may be caused by seborrheic alopecia, malnutrition, microbial infection and other reasons. 1. Seborrheic alopecia: mainly related to heredity and androgen abnormality, both men and women can suffer from the disease, mostly men, men’s early manifestation of the forehead on both sides of the hair began to thin, sparse, and then gradually fall off, female patients with less severe symptoms, mostly for the top of the head hair gradually thinning, in addition to the symptoms of alopecia, accompanied by an increase in oil secretion of the scalp, dandruff, itching and other symptoms. 2. Malnutrition: Iron deficiency anemia and certain nutrient deficiencies caused by excessive weight loss and chronic diseases can also lead to hair thinning on both sides. 3. Microbial infections: when the hair on both sides is infected by fungus or bacteria, it is easy to destroy and damage the hair follicles, thus causing permanent hair loss and the symptoms of hair thinning on both sides. Hair thinning on both sides may also have other causes, it is recommended to go to the hospital in a timely manner to improve the examination, to clarify the cause of the disease and follow the doctor’s instructions for treatment.