A method for exercising or preventing and treating chronic diseases by sunlight. Mainly let the sun shine on human skin, causing a series of physical and chemical reactions, in order to achieve the purpose of fitness and treatment. Sunbathing is often combined with cold water bath and air bath. According to the wavelength of sunlight, there are three kinds of light that can be used for exercise: ① infrared rays with a wavelength above 760 nm. ② Visible light with wavelength of 400 ~ 760 nm. (3) ultraviolet with the wavelength of 180 ~ 400 nm. These three kinds of rays have different effects on human body. Infrared rays can penetrate the epidermis and reach deep tissues, so that the temperature of irradiated tissues increases, blood vessels dilate, blood flow accelerates and blood circulation improves; If the radiation is intense for a long time, the whole body temperature can be raised. It can be seen that light can cheer people up and make them feel comfortable through vision and skin. Ultraviolet is the strongest spectrum in sunlight, which can strengthen blood circulation, promote the process of substance metabolism, convert ergosterol in skin into vitamin D, regulate calcium and phosphorus metabolism, and promote the normal development of bones. The method of sunbathing generally adopts direct irradiation, which can be taken in a lying position or sitting position, but it must be carried out step by step. Generally, lower limbs and back are irradiated first, and then upper limbs and chest and abdomen are irradiated; You can cover your head with white towels and straw hats, and wear sunglasses to protect your head and eyes from the sun. The irradiation time should be controlled according to altitude, season and individual reaction after irradiation. For example, the plateau is stronger than the flat, containing more ultraviolet rays, and the sunshine is strongest at noon in summer, and the irradiation time is shorter; The amount of ultraviolet rays in the sunlight in winter is about 1/6 of that in summer, and the irradiation time can be appropriately extended. Sunbathing usually starts in 5 minutes, and then it can be increased by 5 minutes each time. If the whole body reacts well, it can be extended to 1 ~ 2 hours. Sunbathing places should be clean, flat and dry. If you have headache, palpitation, nausea, general malaise or slight skin burn during sunbathing, stop immediately.