Loose neck skin can be caused by age, excessive weight loss, sun exposure, etc. 1. Age: With age, the collagen and elastin contained in the skin gradually decreases, so the neck skin will appear loose. 2. Excessive weight loss: fat and muscle are the biggest support for the skin. If you lose weight excessively, the subcutaneous fat and muscle will be lost rapidly, which will cause the skin of the neck to lose its support and sagging phenomenon. 3. Sun exposure: frequent exposure to sunlight can lead to changes in skin structure, collagen, elastic fiber reduction and subcutaneous fat loss, so that the neck skin slowly lose elasticity and cause skin laxity. Neck skin laxity is mostly seen in physiological phenomenon, usually without treatment. If accompanied by neck pain, muscle stiffness and other phenomena, it is recommended to consult a doctor in a timely manner to clarify the cause of the disease and follow the doctor’s instructions for treatment.