Thinning eyebrows can be caused by heredity, seborrheic dermatitis, and generalized baldness. 1. Heredity: According to research, if both or one of the parents have thinning eyebrows, there is a certain hereditary rate in the next generation. 2. Seborrheic dermatitis: Seborrheic dermatitis may be related to heredity, infections, immune dysfunction and other factors, and is most common on the scalp, face and other parts of the sebaceous secretion, manifesting itself as yellowish-red patches on the surface of the skin, which are covered with oily scales and accompanied by itching. When seborrheic dermatitis involves the eyebrows, it may lead to eyebrow hair loss and the symptoms of sparse eyebrows. 3. Generalized baldness: a serious type of baldness, in addition to hair loss, there is a generalized loss of hair on the whole body, such as eyebrows, eyelashes, and so on. It is recommended to go to the hospital in time to see a doctor to clarify the cause of the disease and then give targeted treatment.