Prickly Heat Health Article

Definition

Prickly heat is a common disorder of the sweat glands characterized by a red, itching, prickling rash following exposure to high environmental temperatures.

Description

Prickly heat is also known as heat rash, sweat retention syndrome, and miliaria rubra. This disorder occurs during the summer months or year-round in hot, humid climates, and is caused by blockage of the sweat glands. The skin contains two types of glands: one produces oil and the other produces sweat. The sweat glands are coil-shaped and extend deep into the skin. Blockage can occur at several different depths, producing four distinct skin rashes:

• Miliaria crystallina. This is the most superficial blockage and affects only the thin upper layer of skin, the epidermis. Sweat that cannot escape to the surface forms little blisters. A bad sunburn as it just starts to blister can look exactly like miliaria crystallina.
• Miliaria rubra. Blockage at a deeper layer causes sweat to seep into the living layers of skin, causing irritation and itching.
• Miliaria pustulosais. A complication of miliaria rubra in which the sweat is infected with pyogenic (pus-producing) bacteria and contains pus.
• Miliaria profunda. The deepest of all blockages causes dry skin and possibly goose bumps.

These four types of heat rash can cause complications because they prevent sweat from cooling the body, as normally occurs when the sweat evaporates from the skin surface. Sweating is the most important human cooling mechanism available in hot environments. If it does not work effectively, the body can rapidly become over-heated, with severe and potentially fatal consequences.

Causes & symptoms

The best evidence to date suggests that bacteria form the plugs in the sweat glands. These bacteria are probably normal inhabitants of the skin, and why they suddenly interfere with the free flow of sweat is not understood.

Heat rash appears suddenly and has a hot, itching, prickling sensation. Infants are more likely to get miliaria rubra than adults. Obese persons are also more susceptible to heat rash. All the sweat retention rashes are also more likely to occur in hot, humid weather.

Failure to secrete sweat can cause the body to overheat. Before the patient suffers heat stroke, there will be a period of heat exhaustion symptoms (dizziness, thirst, weakness) when the body is still effectively maintaining its normal temperature. Then the patient's temperature rises, often rapidly, to 104 or 105° F (40° C) and beyond. Heat stroke is an emergency that requires immediate and rapid cooling. The best method of treatment is immersion in ice water.