Miliaria, also called heat rash, sweat rash, or prickly heat, is a skin disease marked by small, itchy rashes due to sweat trapped under the skin by clogged sweat-gland ducts. Miliaria is a common ailment in hot and humid conditions, such as in the tropics and during the summer. Although it affects people of all ages, it is especially common in children and infants due to their underdeveloped sweat glands. Signs and symptoms
Symptoms of miliaria include small, red rashes, called papules, which are irritated and itchy. These may simultaneously occur at a number of areas on a patients body, the most common including the upper chest, neck, elbow creases, under the breasts, and under the scrotum. Other areas include skin folds and areas of the body that may rub against clothing, such as the back, chest, and stomach. A related and sometimes simultaneous condition is folliculitis, where hair follicles become plugged with foreign matter, resulting in inflammation. The symptoms relating to miliaria should not be confused with shingles, as they can be very similar. Shingles is limited to one side of the body, but also has a rash-like appearance. It is also accompanied by a prickly sensation and pain throughout the region. Those who suspect they have shingles and not miliaria should seek medical advice immediately as the sooner antivirals are taken, the better. Types
Miliaria can be classified according to the top level at which obstruction occurs in the sweat glands.
In cases where the rash has developed into open blisters or pustular lesions, a doctor should be consulted since more aggressive, medically monitored treatment may be required. See also
Cholinergic urticaria
Sweat allergy

References
External links
DermNet hair-nails-sweat/miliariaPrickly Heat at Merck Manual of Diagnosis and Therapy Home Edition - with pictures
WebMd Description
Clinical pictures of heat rash/prickly heat - Skinsight