Prickly heat (also called Heat rash, Sweat rash, or Miliaria) is a harmless but very itchy skin rash with small red spots all over the affected areas.  The rash is caused by a blockage and inflammation of sweat ducts during times of exposure to heat and high humidity.  These blocked sweat ducts cause sweat to escape into adjacent tissue thus producing the itching and prickling sensations associated with the condition.  The skin contains two types of glands: one produces oil and the other produces sweat.  Sweat glands are coil-shaped and extend deep into the skin.  They are capable of plugging up at several different depths, producing distinct skin rashes.
Prickly heat usually occurs on clothed parts of the body, such as the back, abdomen, neck, upper chest, groin, or armpits and goes away on its own within a few days.  The rash looks like tiny, pink bumps surrounded by a zone of red skin.  Occasionally, some are pinpoint-size water blisters. 
The rash can be itchy or feel prickly, due to overheating, hence it is called "Prickly heat."  In severe forms, however, heat rash can interfere with the body's heat-regulating mechanism and cause fever, heat exhaustion and even death. 

Young children
Heat rash occurs most often in hot, humid conditions, but you may develop it in cool weather if you are overdressed.  The condition usually appears a few days to a few months after exposure to a hot, humid environment.  It's most common in infants.  Active people, newborns in incubators and bedridden patients with fever also are more likely to get heat rash.  In hospital, Miliaria is typically seen on the backs of people who are lying for prolonged periods in bed, particularly when they are sweating from an infection or heart attack, or have been immobilized by a stroke, head injury or orthopaedic operation. 
In young children, prickly heat can appear on the head, neck and shoulders.  It can happen to a baby in very hot weather.  When it's hot and humid outside, your child sweats to cool down.  If he sweats so much that his skin pores clog and sweat can't get out, heat rash develops.  Young children are particularly prone to heat rash because they have smaller pores than adults do.  Tight or heavy clothing can trap the sweat as well, contributing to the irritation.  A child can also get heat rash when he has a high fever that's making him sweat heavily.   Lots of children get it during hot, humid weather when sweat glands are overworked.  Infants can also get it in the wintertime with fever, overdressing, or any local applications applied to the chest for coughs, as they block off the sweat glands.  Older children can get it with exercise.

Symptoms
Tiny red spots, which usually appear on areas of the body where sweat collects, such as the armpits, back, under the breasts, chest, groin,  elbows, knees and the waist. 
Irritating itch and prickling sensation. 
Redness and mild swelling of the affected area.
When a rash is present, it is important to watch for signs of a skin infection. With treatment, heat rash usually clears up completely in 2 to 3 days.  Once triggered off, an attack of Miliaria commonly lasts 5-6 weeks despite the best treatment that can be offered.  Treatment.
The key to treating Sweat rash/Prickly heat is to avoid excessive heat and humidity.  Wearing loose cotton clothing will help prevent it.  Avoid clothing that traps heat and moisture.  Cool baths and air conditioning are very helpful.  Stay in cool or air-conditioned, or well-ventilated environments.  Use a fan if necessary.  Take frequent cool baths or showers.  Dry yourself thoroughly and dust bland types of powder (such as unperfumed talcum powder) on body creases and affected areas.  Do not scratch.  Avoidance of excessive clothing, friction from clothing, excessive soap and contact of the skin with irritants will reduce the liability to Miliaria. 
In case of a toddler having sweat rash, start by cooling off your toddler.  Loosen or remove his clothing and move him into an airy room or shady spot.  Then cool the affected areas directly using cold wet washcloths.  A tepid bath can also help.  Let the air dry his skin as much as possible rather than using towels.  Avoid ointments and other lotions since they can make the rash worse by trapping moisture in the skin.  If the weather stays hot at night where you live, turn on the air-conditioning or place a fan near your child's bed. 
The author is a Dermatologist and can be contacted on 23131257 or by E-mail : vandanjp@hotmail.com