What is heat rash? Heat rash is one of many different types of rash. Rash is a symptom that causes the affected area to turn red and blotchy and swell. The rash may cause spots that are bumpy, scaly, flaky, or filled with pus. Rashes can vary in location, pattern and extent and may occur in any area of the body. Heat rash, also called prickly heat or miliaria, occurs when sweat becomes trapped under your skin. Sweating is a self-regulating mechanism your body uses to maintain a constant temperature. Your sweat-producing glands are located in the middle layer of the epidermis, which is the outer layer of skin. If these glands become clogged and are unable to function, a rash may appear in the affected area. The rash may take one of several forms; it may be clear, skin-colored or reddened. Heat rash can occur for a variety of reasons, such as wearing too much clothing or using blankets when hot. An individual’s anatomy can also lead to heat rash if there are folds or creases between areas of the skin where sweat can collect. Lotions and creams can clog the pores, along with the sweat glands, as well, producing heat rash. The trapped sweat leads to the development of clear, raised bumps that indicate the areas of blockage. These bumps are usually not itchy if they occur as a result of a blockage toward the top layer of skin. Repeated or prolonged outbreaks can lead to an infection in the deeper layers of the epidermis and produce itchy, flesh-colored bumps. Although heat rash itself is generally not serious, it may be a symptom of heat stroke, a life-threatening condition that, left untreated, can lead to organ failure. Seek immediate medical care (call 911) for serious symptoms, including high fever (higher than 101 degrees Fahrenheit); extreme thirst and dehydration; flushed appearance; weakness; rapid heart rate; shallow, rapid breathing; or changes in mental status, such as confusion or forgetfulness.