Unilateral breast gland enlargement in girls may be caused by normal physiological factors, or it may be caused by breast hyperplasia, breast fibroadenoma and other diseases. 1. Physiological factors: due to age, individual differences and nutrition and other physiological factors, the girl’s unilateral breast gland development and enlargement is usually a normal physiological situation, usually do not need to intervene, observe the changes at any time. 2. Mammary gland hyperplasia: the enlargement of unilateral breast gland of girls may also be caused by mammary gland hyperplasia, which is a benign breast disease. It usually presents with breast lumps and periodic breast pain, similar to the development of mammary glands. 3. Mammary fibroadenoma: The occurrence of this disease is related to the imbalance of estrogen levels in the body and the body’s oversensitivity to estrogen, which can also cause unilateral breast gland enlargement in girls. Girls’ unilateral breast gland enlargement can also be caused by other reasons, parents are advised to take girls to the doctor in time to clarify the cause of the disease and then carry out targeted treatment or treatment. At the same time, it is important to maintain a good state of mind and a regular routine, and to avoid a high-fat, high-calorie diet.