Eight-year-old girls with soreness to the touch of one breast may be due to mammary gland development, or may be due to trauma, contact dermatitis and other diseases. 1. Mammary gland development: eight-year-old girls in puberty, their breasts due to fluctuations in the body estrogen and progesterone, can appear on one side of the breast touching the situation of pain. 2. Trauma: If an eight-year-old girl’s breast is impacted, it may lead to poor local blood circulation and a painful touch on one breast. It can also be accompanied by redness, swelling, pain and other symptoms. 3. Contact dermatitis: If the breast skin is stimulated by exogenous substances, resulting in skin-induced contact dermatitis. Girls can have symptoms such as pimples, erythema, edema, swelling, pain, burning and so on, manifested by a painful sensation of touching one side of the breast. There are many reasons why an eight-year-old girl’s breast is painful to touch, and it is recommended that parents bring their children to regular hospitals in a timely manner to carry out the relevant examinations, so as to identify the cause of the disease.