Sunbathing your back in the sun through your clothes may be effective. If the purpose of sunbathing your back in the sun is to get rid of the cold, then sunbathing your back through your clothes is a way to get rid of the cold in your back. However, if you let the sun’s ultraviolet rays irradiate your body through your clothes in order to promote calcium absorption, and synthesize less vitamin D that your body needs, then vitamin D is less effective in promoting calcium absorption. However sunbathing back tanning is also not recommended when the skin is directly exposed to strong sunlight. However, when the sun is not very strong, you can expose your arms, back, feet and other parts of your body, which can better absorb ultraviolet rays. However, cover your head and eyes with a sun hat and sunglasses to avoid damage to your eyes and facial skin from direct sunlight. You should take precautions when sunbathing to avoid sunburn.