The mammary gland is a sex organ that develops during puberty in adult females, and is located on the superficial surface of the pectoralis major muscle, which should grow symmetrically under normal circumstances. Asymmetrical breast growth is common in several situations: 1, the two sides of the mammary glands for the body’s hormone sensitivity has a difference, easy to lead to the mammary glands are still asymmetrical after maturity, this situation belongs to the congenital mammary gland development abnormality. Slight asymmetry can be corrected by wearing special underwear, too obvious may need surgery to correct the treatment. 2, if currently in the adolescent development period, this breast asymmetry is a normal phenomenon, until the development of maturity of the two sides of the mammary glands will be close to symmetry. 3, poor sleeping posture affects the development of the mammary glands, such as usually favor the right side of the lying position, the right side of the development of the pressure is affected. In either case, it is recommended to go to a regular hospital for treatment.