Red foot sprain may be the normal performance after injury, or it may be caused by local infection and so on. 1. Normal performance: ankle sprain will lead to injury local capillary rupture, resulting in local blood circulation disorders, while the contents of the blood vessels free to the tissue gap, the contents can not enter the microcirculation of the capillaries and the venous system in a timely manner, may lead to sprain local redness of the symptoms. 2. Localized infection: If the sprain is not properly treated or there is an open wound without debridement, it may cause localized infection at the sprain site, and redness may appear, accompanied by severe pain at the sprain site, elevated local skin temperature, swelling, increased exudation and other symptoms. If the redness after ankle sprain is not relieved, or accompanied by other symptoms, you should go to the hospital in a timely manner, to clarify the cause and then give targeted treatment.