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The Skin's Function
The skin's job is to protect the inside of the body from the outside world, and acts as a preventive barrier against intruders (for example, infection, chemicals, or ultraviolet light). It also plays an important role in the body's temperature control. One way that the body cools itself is by sweating, and allowing that sweat or perspiration to evaporate. Sweat is manufactured in sweat glands that line the entire body (except for a few small spots like fingers, toenails, and the ear canal).
Sweat glands are located in the dermis or deep layer of the skin, and are regulated by the temperature control centers in the brain. Sweat from the gland gets to the surface of the skin by a duct.
What Is Heat Rash?
A heat rash occurs when sweat ducts become clogged and the sweat can't get to the surface of the skin. Instead, it becomes trapped beneath the skin's surface causing a mild inflammation or rash. Common names for heat rash include prickly heat or miliaria. Other heat rashes include heat urticaria (hives) and sweat retention. Heat rash is prevalent in the summer months and particularly in humid climates. The condition usually is self-limited and resolves in hours to a few days without treatment. Rarely, it may be more severe requiring professional medical care.
What Are the Symptoms of Heat Rash in Children and Adults?
The common symptoms of heat rash are red bumps on the skin, and an itchy or prickly feeling to the skin. These are due to inflammation of the superficial layers of the skin and the prickly sensation is similar to the feeling of mild sunburn. The symptoms of heat rash are the same in infants and adults; however, since an infant can't complain about the rash sensation, he or she may be fussy.
Any body part may be affected. Areas characteristically affected by heat rash include the face, neck, back, abdomen, groin, under the breasts, elbow folds, and buttocks.
Heat Rash Types
There are four types of heat rash (miliaria):
- Clear (miliaria crystalline),
- Red (miliaria rubra),
- White/Yellow (miliaria pustulosa),
- Deep (miliaria profunda).
Clear Heat Rash (Miliaria Crystalline)
Tiny blisters that look like small beads of sweat are seen if the sweat is blocked at the most superficial layers of the skin where the sweat duct opens on the skin surface. Miliaria crystalline has no symptoms other than these "sweat bubbles."
Red Heat Rash (Miliaria Rubra)
If the sweat causes inflammation in the deeper layers of the epidermis, the classic heat rash occurs, which is referred to as miliaria rubra. Like any other inflammation, the area becomes red (and therefore the name rubra) and the blisters become slightly larger. Because the sweat glands are blocked and don't deliver sweat to the skin's surface, the area involved is dry and can be irritated, itchy, and sore. This rash is also called prickly heat.
White/Yellow Heat Rash (Miliaria Pustulosa)
When pustules (collections of pus) develop in lesions of miliaria rubra, the term miliaria pustulosa is used.
Deep Heat Rash (Miliaria Profunda)
Less commonly, after repeated episodes of prickly heat, the heat rash may inflame the deeper layer of the skin called the dermis, and cause miliaria profunda. This rash is made up of larger, harder bumps that are more skin colored. The rash begins almost immediately after exercise, and no sweat can be found on the affected areas. This type of heat rash may be potentially more dangerous if enough skin is involved, since the lack of sweating can lead to heat-related illnesses like heat cramps, heat exhaustion, or heat stroke.
What Are the Causes of Heat Rash?
It is uncertain why some people get heat rashes and others don't. As mentioned, sweat gland ducts can get blocked if excessive sweating occurs, and that sweat is not allowed to evaporate from a specific area. Some examples of how blockage may occur include the following:
- Creases in the skin like the neck, armpit, or groin have skin touching adjacent skin, which makes it difficult for air to circulate, preventing sweat evaporation.
- Tight clothing that prevents sweat evaporation.
- Bundling up in heavy clothing or sheets. This may occur when a person tries to keep warm in wintertime or when chilled because of an illness and fever.
- Heavy creams or lotions can clog sweat ducts.
- Heat rash may occur as a side effect of some medications (for example, isotretinoin [Accutane] or clonidine [Catapres]).
Who Is At Risk for Heat Rash?
Newborns, infants, and the elderly are at risk for developing heat rash. They are especially at risk if they are immobile for long periods of time and parts of the skin aren't exposed to circulating air, which results in the inability of the sweat ducts to "breathe" (evaporative cooling). Heat rashes are more common in places with hot, humid climates because people sweat more. Intense exercise associated with lots of sweating may cause a heat rash, especially if the clothing worn does not allow adequate air circulation.
Why Are Babies So Prone to Heat Rash?
Babies have immature sweat glands that aren't able to get rid of all the sweat they produce, which can cause a heat rash if they are exposed to warm weather, are overdressed, excessively bundled, or have a fever.
How Is Heat Rash Diagnosed?
The diagnosis of heat rash or prickly heat is made by physical examination. Knowing that the rash appears during sweating or heat, appreciating the location on the body (in skin creases or where clothes fit tightly) and seeing what the rash looks like is enough to make the diagnosis. As with many rashes, the health care practitioner can look at the involved skin and make the diagnosis.
Persistent heat rash is typically diagnosed from the characteristic skin appearance on exam and a history of recent heat exposure. Atypical or more resistant cases of heat rash may require skin culture, microscopic exam from skin scrapings, or less commonly a microscopic exam from a skin biopsy (surgically removing a very small piece of skin using a local anesthetic). Additional tests may be required to exclude other causes of skin rashes such as bacterial infections, allergic reactions, eczema, and fungal infections.
Home Remedy Treatments for Heat Rash
Heat rash often resolves on its own when the skin cools. If the prickly sensation persists, calamine lotion may be helpful. Some clinicians also recommend over-the-counter hydrocortisone creams or sprays. Some people suggest that vitamin A or vitamin C creams may be effective to treat heat rash, and though there is no evidence that they work, there is little harm in these treatments.
Medical Treatment for Heat Rash
Heat rash or prickly heat resolves on its own once the skin cools, but on occasion the sweat glands can become infected. The signs of infection include pain, increased swelling, and redness that does not resolve. Pustules may form at the site of the rash. This infection occurs because bacteria have invaded the blocked sweat gland. Antibiotic treatment may be required. Chronic and recurrent heat rash may need to be treated by a health care practitioner or dermatologist (skin specialist).
How Can Heat Rash Be Prevented?
Prevention is the most important treatment for heat rash. By allowing the skin to be exposed to circulating air, the potential for sweat glands to become inflamed decreases.
Other strategies to prevent heat rash include:
- avoid exercising in hot, humid weather,
- wear loose clothing made of breathable fabrics like cotton,
- use air conditioning, and
- keep the skin clean with frequent baths or showers to prevent sweat glands from becoming clogged.
How to Protect Yourself When Temperatures Are Extremely High
The body can adapt very well in hot weather, but it takes time to acclimate. The actual temperature is just one factor when a person decides to work, play, or exercise in the heat. The heat index adds humidity to the equation since sweat cannot evaporate if the water content in the air (humidity) is high. If the air holds as much water as it can there is no place for sweat to go, and evaporation cannot cool the body.
To avoid heat-related illnesses, avoid working or exercising in extreme heat. If it is required, to avoid dehydration and other complications, take frequent breaks to get out of the heat and drink plenty of fluids to replenish fluid lost via sweat.
How Much Water Should I Drink in Hot Weather?
It is hard to gauge how much water is lost through sweat, and the thirst mechanism may not be sensitive enough to remind a person to drink enough. In general, the kidneys are a good guide to whether there is enough water in the body. If the body is dehydrated, the kidneys will try to hold on to as much water as possible. Symptoms and signs of the kidneys preserving water are decreased urine production, urine concentrated in color, and a strong urine odor. Urine is clear when there is enough fluid in the body.
In a hot environment, a person should drink enough water to make the urine clear, and make sure the body is producing sweat.
Should I Take Salt Tablets During Hot Weather?
Taking salt tablets is rarely a good idea. While the body loses many electrolytes when it sweats, there are mechanisms in place to compensate for the loss. Usually, keeping the body hydrated with plain water is adequate but does not resupply electrolytes. Sports drinks (for example, Powerade, Gatorade) may be reasonable alternatives.
What Is the Best Clothing for Hot Weather or a Heat Wave?
Evaporation works to cool the skin only if the sweat that the body produces is allowed to evaporate. Lightweight, loose clothing allows air circulation to the body's surface and helps promote cooling. While cotton is the classic fabric that can be used, some synthetic fabrics have been developed to wick sweat from the skin and allow more efficient skin or body cooling.
More Reading on Heat-Related Illnesses