Thinning hair in 5-month-old babies may be caused by genetic factors, nutritional deficiencies, improper care and other factors. 1. Hereditary factors: if the parents in the childhood hair thinning situation, may be inherited to the child, will lead to 5 months baby hair is relatively small, with the gradual growth of the baby, may be hair will gradually increase. 2. Nutritional deficiencies: If the 5-month-old baby body lacks some nutrients, such as calcium, zinc, etc., may lead to hair thinning, may also be accompanied by restless sleep, sweating and other abnormalities, and when the seriousness will affect the physical development. 3. Improper care: parents in the baby wash hair, often use stimulating cleaning supplies, and wash more often, may cause stimulation of the hair follicles, will affect the growth of hair, will make hair thinning. More than 5 months baby hair thinning, and accompanied by other abnormalities, it is recommended that parents take their children to the doctor to avoid adverse effects.