The net-like lines on the neck like stretch marks are called expansion lines, which may be caused by excessive weight gain, puberty, the use of glucocorticoid hormone drugs, and short-term obesity. 1. Excessive weight gain: muscle growth is too fast, more than the skin’s own extension speed, it will lead to dermal elastic fibers are pulled off, thus forming expansion lines. 2. Puberty: The faster growth and development during puberty may cause the dermal collagen in the skin to be pulled, resulting in swelling lines. 3. Use of glucocorticoid drugs: long-term use of glucocorticoid drugs may lead to inhibition of collagen fibers and elastic fibers in the skin, resulting in the collapse of elastic fibers, thus causing swelling lines. 4. Short-term obesity: If the rate of fat deposition is too fast, it will lead to dermal elastic fibers and collagen fibers being pulled, which will also cause swelling lines. Moderate exercise helps skin elasticity recovery, avoid excessive intake of carbohydrates and calories food. Patients are advised to go to the hospital in time, under the guidance of the doctor, to avoid private medication.