Hair thinning in one year old babies may be related to improper care, lack of sleep, malnutrition and so on. 1. Improper care: If you give your baby frequent use of adult shampoo to wash their hair, it may cause damage to the scalp and cause hair thinning. 2. Lack of sleep: lack of sleep and poor sleep quality can affect the growth and development of the child and may also cause hair thinning. 3. Malnutrition: Babies who are anorexic or picky eaters can cause a lack of vitamins or trace elements, which can affect hair growth. One year old baby hair thinning may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor’s treatment.