prickly heat

Also found in: Dictionary, Thesaurus, Encyclopedia, Wikipedia.

Prickly Heat



Also known as sweat retention syndrome or miliaria rubra, prickly heat is a common disorder of the sweat glands.


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 four distinct skin rashes.
  • Miliaria crystallina is the most superficial of the occlusions. At this level, only the thin upper layer of skin is affected. Little blisters of sweat that cannot escape to the surface form. A bad sunburn as it just starts to blister can look exactly like this.
  • Deeper plugging causes miliaria rubra as the sweat seeps into the living layers of skin, where it irritates and itches.
  • Miliaria pustulosais (a complication of miliaria rubra) occurs when the sweat is infected with pyogenic bacteria and turns to pus.
  • Deeper still is miliaria profunda. The skin is dry, and goose bumps may or may not appear.
There are two requirements for each of these phases of sweat retention: hot enough weather to induce sweating, and failure of the sweat to reach the surface.

Causes and symptoms

Best evidence as of 2001, 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 sweat flow is still not known.
Infants are more likely to get miliaria rubra than adults. All the sweat retention rashes are also more likely to occur in hot, humid weather.
Besides itching, these conditions prevent sweat from cooling the body, which it is supposed to do by evaporating from the skin surface. Sweating is the most important cooling mechanism available in hot environments. If it does not work effectively, the body can rapidly become too hot, with severe and even lethal consequences. Before entering this phase of heat stroke, there will be a period of heat exhaustion symptoms-dizziness, thirst, weakness-when the body is still effectively maintaining its temperature. Then the temperature rises, often rapidly, to 104-5°F (40°C) and beyond. This is an emergency of the first order, necessitating immediate and rapid cooling. The best method is immersion in ice water.


Rash and dry skin in hot weather are usually sufficient to diagnose these conditions.


The rash itself may be treated with topical anti-pruritics (itch relievers). Preparations containing aloe, menthol, camphor, eucalyptus oil, and similar ingredients are available commercially. Even more effective, particularly for widespread itching in hot weather, are cool baths with corn starch and/or oatmeal (about 0.5 lb [224 g] of each per bathtub-full).
Dermatologists can peel off the upper layers of skin using a special ultraviolet light. This will remove the plugs and restore sweating, but is not necessary in most cases.
Much more important, however, is to realize that the body cannot cool itself adequately without sweating. Careful monitoring for symptoms of heat disease is important. If they appear, some decrease in the ambient temperature must be achieved by moving to the shade, taking a cool bath or shower, or turning up the air conditioner.


The rash disappears in a day with cooler temperatures, but the skin may not recover its ability to sweat for two weeks-the time needed to replace the top layers of skin with new growth from below.


Experimental application of topical antiseptics like hexachlorophene almost completely prevented these rashes.



Berger, Timothy G. "Skin and Appendages." In CurrentMedical Diagnosis and Treatment, 1996, edited by Stephen McPhee, et al., 35 the ed. Stamford:Appleton & Lange, 1995.

Key terms

Ambient — Surrounding.
Pyogenic — Capable of generating pus. Streptococcus, Staphococcus and bowel bacteria are the primary pyogenic organisms.
Syndrome — A collection of abnormalities that occur together often enough to suggest they have a common cause.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


1. energy that raises the temperature of a body or substance.
2. estrus.
3. a rise in temperature.
4. to cause to increase in temperature.

Heat is associated with molecular motion, and is generated in various ways, including combustion, friction, chemical action, and radiation. The total absence of heat is absolute zero, at which all molecular activity ceases.
Body Heat. Heat Production. Body heat is the byproduct of the metabolic processes of the body. The hormones thyroxine and epinephrine increase metabolism and consequently increase body heat. Muscular activity also produces body heat. At complete rest (basal metabolism) the amount of heat produced from muscular activity may be as low as 25 per cent of the total body heat. During exercise or shivering the percentage may rise to 60 per cent. Body temperature is regulated by the thermostatic center in the hypothalamus. A body temperature above the normal range is called fever.
Heat Loss. Loss of body heat occurs in three ways: by radiation (heat waves), by conduction to air or objects in contact with the body, and by evaporation of perspiration. Some body heat is lost in exhalation of air and in elimination of urine and feces.
Applications of External Heat. Purposes. Local applications of heat may be used to provide warmth and promote comfort, rest, and relaxation. Heat is also applied locally to promote suppuration and drainage from an infected area by hastening the inflammatory process; to relieve congestion and swelling by dilating the blood vessels, thereby increasing circulation; and to improve repair of diseased or injured tissues by increasing local metabolism.
Effects. Factors that determine the physiologic action of heat include the type of heat used, length of time it is applied, age and general condition of the patient, and area of body surface to which the heat is applied. Moist heat is more penetrating than dry heat. Prolonged applications of heat produce an increase in skin secretions, resulting in a softening of the skin and a lowering of its resistance. Extreme heat produces constriction of the blood vessels; moderate heat produces vascular dilation. Repeated applications of heat will result in an increased tolerance to heat so that the individual may be burned without being aware of it. Elderly persons and infants are more susceptible to burns from high temperatures.

Heat applied to an infected area can localize the infection; for this reason, external heat should not be applied to the abdomen when appendicitis is suspected, because it may lead to rupture of the inflamed appendix.
heat exhaustion a disorder resulting from overexposure to heat or to the sun; long exposure to extreme heat or too much activity under a hot sun causes excessive sweating, which removes large amounts of salt and fluid from the body. When salt and fluid levels fall too far below normal, heat exhaustion may result. Called also heat prostration.
Symptoms. The early symptoms are headache and a feeling of weakness and dizziness, usually accompanied by nausea and vomiting. There may also be cramps in the muscles of the arms, legs, or abdomen. These first symptoms are similar to the early signs of sunstroke, or heat stroke, but the disorders are not the same and should be treated differently. In heat exhaustion, the person turns pale and perspires profusely. The skin is cool and moist, pulse and breathing are rapid, and body temperature remains at a normal level or slightly below (in sunstroke the body temperature may be dangerously elevated). The patient may seem confused and may find it difficult to coordinate body movements; loss of consciousness seldom occurs.
Treatment. In cases of heat exhaustion, the victim should lie quietly in a cool place until transported to an emergency facility. The restoration of normal blood volume will be a priority. Stabilization of electrolytes is also important. If the person is able to safely swallow, sips of cool replacement fluid should be provided. Measures to reduce body temperature are employed.

If the condition is accompanied by cramps, the pain may be relieved by lightly stretching the affected muscles in addition to administering replenishing fluids. In cases of severe heat exhaustion and cramps, hospitalization may be necessary. Serum electrolyte levels are monitored to guide adequate replacement.
Prevention. Heat exhaustion and other heat disorders may be prevented by avoiding long exposure to sun or heat. The elderly, the very young, individuals with chronic diseases, and athletes exercising in the sun are at high risk. When the weather is very hot, or when working in an extremely hot place, it is essential to maintain adequate hydration. Regular rest periods are necessary. In the event of weakness or dizziness, persons should stop working at once and rest in a cool place.

It is possible for indoor temperatures to exceed the outdoor temperature. Poor ventilation can lead to an unhealthy situation that contributes to heat exhaustion. For this reason, adequate temperature control indoors is important in prevention of serious health problems.
latent heat the amount of heat absorbed or given off by a body without changing temperature, as when it undergoes a change of state.
prickly heat (heat rash) miliaria.
specific heat the ratio of the heat capacity of a substance to that of water; it is equivalent to the amount of heat required to raise the temperature of one gram of the substance by one degree Celsius, since the corresponding value for water is defined as 1.0.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

mil·i·a·ri·a ru·'bra

an eruption of pruritic macules with small central vesicles at the orifices of sweat glands, accompanied by redness and inflammatory reaction of the skin.
Farlex Partner Medical Dictionary © Farlex 2012

prickly heat

The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


A condition characterised by multiple vesicles associated with increased heat, moisture and occlusion.
Clinical findings
Pruritus, hypohidrosis, irritability.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.

prickly heat

Miliaria, see there.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.

mil·i·a·ri·a ru·bra

(mil'-ē-ā'rē-ă rū'bră)
An eruption of papules and vesicles at the orifices of sweat glands, accompanied by redness and inflammatory reaction of the skin.
Synonym(s): heat rash, prickly heat, strophulus, tropical lichen, lichen tropicus.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

prickly heat

An irritating skin disorder caused by excessive sweating so that the skin becomes waterlogged, the ducts of the sweat glands blocked and sweat is forced into the skin. The condition settles if the affected person can be kept cool by air conditioning or frequent cool showers. Also known as miliaria rubra.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
References in periodicals archive ?
Clockwise from far left - sunburn, travel sickess, bites and prickly heat, all can be avoided on your holidays Clockwise from far left - sunburn, travel sickess, bites and prickly heat, all can be avoided on your holidays
Babies and children are more likely to be affected by prickly heat than adults because their sweat glands are underdeveloped.
We often think of miliaria, commonly known as "prickly heat," as an infant's problem that occurs in hot, humid weather or climates.
Cox's Liniment, Johnson's Prickly Heat Powder and Dr.
--My darling, my little baby girl, Poppy sighs, the notion a cool, sun-washed breeze across the back of his neck, now starting to simmer with an itch, maybe prickly heat,
It could be: 6 Prickly heat (heat rash) which is uncomfortable but usually harmless.
Various skin aliments like heat rashes, fungal disease, prickly heat and acnes (pimples) have increased 50 per cent in hot weather.
Catch prickly heat with these cracking cacti buys 1 SLIKY STUFF Look sharp in this cactus print silky playsuit by Jaded London, PS50, Topshop 2 BRIGHT IDEA Light up your life with a cactus lamp, PS82.50, 3 PUT A RING ON IT The perfect place for your jewellery, this Oliver Bonas ring holder is PS15, 4 SLEEP TIGHT Get a good night's sleep in this pyjama set, PS28, 5 WHERE'S YOUR HEAD AT?
I've written about my various gripes that I have with the summer - the pressure to get out and do something, the hay fever, the wasps, the prickly heat, the wardrobe changes, fake tan obligations, the dilemma over whether to put sun-cream on or get some vitamin D, the heavy-handed use of air-conditioning.
Muscat: The winter is about to set in, bringing much relief from the scorching sun and prickly heat. The sudden fluctuation in the temperature, however, has caused a surge in complaints of seasonal flu across Muscat, say doctors.