What causes a chill in my back the day after a shave?

Scraping causes the capillaries to expand and the pores to enlarge, making it easy for wind and evil to invade from outside, so the back may get cold the next day. Patients should therefore keep warm and can use a hot compress on the back.
Generally speaking, after the stimulation of gua sha or cupping, the next day even a slight pain in the skin is mostly normal and there is no need to worry too much.