Common culprits like heat rash and contact dermatitis tend to share red, itchy symptoms, but they do differ by cause and location. “The best way to manage a heat rash is to keep cool, wear loose clothing and have cool showers. Polymorphic light eruption(Alamy Stock Photo)People often mistake polymorphic light eruption for heat rash because both cause itchy, red bumps, but they are triggered by different things. “Insect bites usually present in a raised red, itchy bump that has local swelling and warmth around the bite, and occasionally blistering.” “Symptoms include tingling or burning shortly after leaving the water, itchy red spots or small raised bumps and occasionally tiny blisters.