The longest common cause is an allergic reaction to the area, which may be caused by contact with a specific allergen, resulting in a localized inflammatory skin reaction and congestion. It is also possible that the area has caused some scalding, but the degree of scalding is not high, such as the formation of first-degree scalding, which may also produce redness of the foot, or it may be a low-temperature burn formed by the patient’s frequent use of hot water to soak the foot. If the formation of redness is more pronounced, there is a possibility of infection, especially soft tissue inflammation caused by bacterial infection, at which point a dermatomycosis is formed, which, if formed, will also be accompanied by significant pain.