Though physical exercise has many benefits, for some, certain adverse side effects can occur. If your legs turn red after exercise, you most likely have nothing to worry about. The stimulation exercises causes in your body can turn your skin red. In some cases, however, the redness on your legs is not related to stimulation but could signal a more serious problem if discoloration is accompanied by pain.
Physical activity, especially aerobic-based exercising such as running, elliptical training or aerobic step workouts, greatly elevates your heart rate. This means blood is pumped through your body more vigorously and your core body temperature rises. In some, an increase in body temperature triggers skin discoloration. Though any part of your body can be affected by this, the legs may be especially prone to turning red. During an activity such as running, for instance, your legs must do a great amount of work, which requires an increase in blood flow to that area for energy.
Cholinergic urticaria, or physically-induced urticaria, is a form of hives triggered by physical causes. As your core body temperature increases during exercise, and your body begins to sweat, your skin may become itchy. If you scratch your skin, hives can begin to appear within minutes and turn the skin red. In most cases, cholinergic urticaria dissipates once the core body temperature lowers after exercises. If the condition is chronic, however, a hives breakout may last 24 hours and leave behind bruises. In general, chronic cholinergic urticaria creates hives that are painful rather than itchy.
Exercise can potentially lead to muscle fatigue or strains. If your leg muscles are overused, they can begin to hurt. Leg pain typically develops over a longer period of time when the muscles are being strenuously trained on a daily basis. This type of muscle fatigue can lead to serious health problems. If your muscles are strained, your legs can appear red and swollen. Redness caused by fatigue can cover larger areas of your leg rather then smaller dots or patches, as with hives. In such a condition, the leg usually hurts or aches. If you experience these types of symptoms, speak to your doctor immediately to determine how to treat your leg.
Another type of rash you can develop during exercise is cold urticaria. The exact cause for these types of hives is unclear, but certain people with sensitive skin can develop cold urticaria when exposed to cold temperatures. This allergic reaction turns the skin red due to an increase in histamine that is released into the dermis because of cold air temperatures. Red, itchy hives begin to develop that generally last up to a half hour. Runners are perhaps most prone to developing cold urticaria when training in cold temperatures wearing shorts instead of long pants. If you experience any chills or swelling of your limbs, stop exercising immediately.