Fine hair is mostly related to heredity, and may also be caused by seborrheic dermatitis and other diseases. 1. Heredity: Hair quality is mainly related to genetic factors, if the parents themselves have fine hair, it will lead to the next generation for the higher chance of fine hair. 2. Seborrheic dermatitis: seborrheic dermatitis can also lead to patients with fine hair, the disease is a chronic inflammatory skin disease that occurs in the seborrheic area, which is common in the head, face, chest and back, etc. The cause of the disease is not yet clear, and it may be related to heredity, sebum metabolism, hormonal abnormalities and other factors, and the patient will also have erythematous rashes, greasiness, flaking, etc. The causes of fine hair are more common than those of the parents, but they are not the only ones who have fine hair. There are many reasons for fine hair, so patients are advised to consult a doctor for a clear diagnosis and symptomatic treatment.