Redness of the Skin
The skin turns red when it is infected with the bacteria that cause cellulitis. You may notice the red part of your skin looks like a rash and looks swollen or is tender to the touch. The redness often begins in one area and gradually spreads to cover more areas on the skin. Sometimes this redness has a well-defined border. At other times, according to the American Academy of Dermatology Association [2], it may be difficult to tell where the redness ends and where your normal skin begins.
It is normal for the redness to spread. You should seek treatment for any signs of cellulitis you notice. However, if the redness appears to be spreading rapidly, it may be a sign of a medical emergency [3]. You should expedite your visit to a doctor so the infection does not worsen.