What causes my arms and legs to turn red while exercising?

When you exercise and when you sweat, your pores open. In addition to your pores opening, blood is rushing through your body and more often than not the redness is due to the stimulation from exercise. Essentially, when blood is rushing through your body and when your heart rate is elevated, your body temperature will elevate which will result in redness of the skin. However, if you experience any pain accompanied with the redness then this may present a bigger problem. If your body starts to itch, try to avoid scratching and consider taking a shower to clean your body. Scratching may cause hives and bruising. In addition, if redness is followed by pain then be cautious and consider resting your body to allow your muscles to recover to prevent excessive wear and tear on your body.