Why does the skin surface ache when it is cold?

The doctor said it was inflammation, not because the skin was broken, but because of poor blood circulation or other reasons. Anyway, it's subcutaneous inflammation, which can't be seen from the outside. I don't remember exactly what I said. That's what it means. I calculated that I accidentally hit it, and the epidermis was not broken, but the capillaries inside were broken, and then there was inflammation, and then that was it. It will be fine in a few days.