Many different types of skin rashes exist. They can be concerning, uncomfortable, or downright painful. One of the most common types of rash is heat rash, also called miliaria.
Prickly heat, also known as miliaria rubra, is an itchy rash of small, raised red spots that causes a stinging or prickling sensation on the skin usually found on body areas covered by clothing. It can develop when the sweat ducts become clogged, can’t expel sweat and swell and often leads to discomfort and itching. This is more likely to happen in warmer months, in warmer climates, and after intense exercise. Wearing certain clothing can trap sweat leading to heat rash and using thick lotions and creams can also lead to heat rash.
It’s possible to get heat rash in cooler temperatures if you wear clothes or sleep under covers that lead to overheating. Babies are more likely to develop heat rash because their sweat ducts are underdeveloped.
In babies, heat rash can be caused by well-meaning parents who dress their baby too warmly, but it can happen to any baby in very hot weather. A baby should be dressed as an adult would be to be comfortable at the same temperature and activity level. Babies' hands and feet may feel cool to your touch but that does not mean they need to be dressed too warmly in hot weather.
Heat rash looks like dots or tiny pimples. In young children, heat rash can appear on the head, neck, and shoulders. The rash areas can get irritated by clothing or scratching, and, in rare cases, a secondary skin infection may develop.
Different types of heat rash can range in severity, and they all look a little different.
Miliaria crystallina is the most common and mildest form of heat rash. If you have miliaria crystallina, you’ll notice small clear or white bumps filled with fluid on the surface of your skin. These bumps are bubbles of sweat. The bumps often burst.
Contrary to popular belief, this type of heat rash doesn’t itch and shouldn’t be painful. Miliaria crystallina is more common in young babies than in adults.
Miliaria rubra, or prickly heat, is more common in adults than in children and babies. Miliaria rubra is known to cause more discomfort than miliaria crystalline because it occurs deeper in the outer layer of the skin, or the epidermis.
Miliaria rubra occurs in hot or humid conditions and may cause:
itchy or prickly sensations
red bumps on the skin
a lack of sweat in the affected area
inflammation and soreness of the skin because the body can’t release sweat through the skin’s surface
Bumps that appear due to miliaria rubra can sometimes progress and be filled with pus. When this happens, doctors refer to the condition as miliaria pustulosa.
Miliaria profunda is the least common form of heat rash. It can recur often and become chronic. This form of heat rash occurs in the dermis, which is the deeper layer of skin. Miliaria profunda typically occurs in adults after a period of physical activity that produces sweat.
If you have miliaria profunda, you’ll notice larger, tough, flesh-coloured bumps.
Classification of miliaria types are based on how deep the blocked sweat ducts are. Because heat rash prevents sweat from leaving your skin, it may lead to nausea and dizziness.
Major Causes of Heat Rash
Heat rash develops when some of your sweat ducts clog. Instead of evaporating, perspiration gets trapped beneath the skin, causing inflammation and rash.
It's not always clear why the sweat ducts become blocked, but certain factors seem to play a role, including:
Immature sweat ducts. A newborn's sweat ducts aren't fully developed. They can rupture more easily, trapping perspiration beneath the skin. Heat rash can develop in the first week of life, especially if the infant is being warmed in an incubator, is dressed too warmly or has a fever.
Tropical climates. Hot, humid weather can cause heat rash.
Physical activity. Intense exercise, hard work or any activity that causes you to sweat heavily can lead to heat rash.
Overheating. Overheating in general — dressing too warmly or sleeping under an electric blanket or sitting too close to a fire or heater — can lead to heat rash.
Prolonged bed rest. Heat rash can also occur in people who are confined to bed for long periods, especially if they have a fever.
Being overweight or obese – which is more likely to lead to excessive sweating.
Heat rash usually heals without problems, but it can lead to infection with bacteria, causing inflamed and itchy pustules.
How is Heat Rash Diagnosed?
Heat rash can usually be identified by its appearance and does not usually require medical attention. But if it doesn't go away after 3 or 4 days, or if it appears to be getting worse, or if your child develops a fever, contact your doctor right away.
When you or your child has a rash, be sure to watch for signs of infection, including:
Increased pain, swelling, redness, or warmth around the affected area.
Red streaks extending from the affected area.
Drainage of pus from the area.
Swollen lymph nodes in the neck, armpit, or groin.
Fever of 100.4°F (38°C) or higher, or chills with no other known cause.
If any of these symptoms develop, contact your doctor immediately.
What is the Treatment for Heat Rash?
Most heat rashes heal on their own. The following steps can help relieve symptoms.
Start by removing or loosening your baby's clothing and move him or her to a cool, shady spot.
Let the skin air-dry instead of using towels.
Apply cool packs over the affected areas (do not leave packs on longer than 20 minutes per hour).
Avoid ointments or other lotions, because they can irritate the skin.
Don't scrub or rub the skin to remove heat rash bumps.
Avoiding overheating may be all you need to do for mild heat rash. Once skin is cool, heat rash tends to clear quickly.
More-severe forms of heat rash may require ointments you apply to your skin to relieve discomfort and prevent complications. Such topical treatments may include:
Calamine lotion to soothe itching
Anhydrous lanolin, which may help prevent duct blockage and stop new lesions from forming
Topical steroids in the most serious cases
Try hydrocortisone cream – low-strength hydrocortisone cream is also available from pharmacies and is effective at treating very itchy and irritated areas of skin. However, avoid using it on your face and always follow the instructions.
Antihistamine tablets may help control itching – but consult your doctor first as they're not always suitable
The following tips can help prevent future episodes of the rash:
Dress your child in as few clothes as possible during hot weather.
Keep the skin cool and dry.
Keep the sleeping area cool.
After the rash is gone, gradually expose your child to warmer temperatures so that his or her skin can acclimate.
Tips for Prevention
Follow these tips to prevent heat rash:
Avoid wearing tight clothing that doesn’t allow your skin to breathe.
Don’t use thick lotions or creams that can clog your pores.
Try not to become overheated, especially in warmer months. Seek out air-conditioning.
Use a soap that won’t dry your skin and doesn’t have fragrances or dyes.
Keep your sleeping area cool and well-ventilated.
Don't wear polyester and nylon fabrics in the summer.
Don't use plastic mattresses or mattress protectors; use a sheepskin underlay if possible.
Heat rash is a minor discomfort that will resolve itself in a matter of days for most people. Talk with your doctor if you believe you may have something more serious or if you have heat rash that frequently recurs.
Conditions That Are Not Heat Rash
Many other rashes can look like heat rash. Some of these other conditions include:
Folliculitis (a bacterial infection of the skin commonly with "staph")
Medication reaction or drug eruption
Grover's disease (also called transient acantholytic dermatosis) causes itchy bumps on the abdomen and chest that worsen with heat)
Niacin medication (in some individuals, cause a temporary overall body flushing and heat rash like appearance that improves in a few hours)
There are a number of conditions that can be called a rash, because a rash is a general term for an outbreak of bumps on the body that changes the way the skin looks and feels.
Heat rash can be confused with other conditions, including viral infections like chickenpox or measles, and bacterial infections such impetigo.
A rash can also be the result of an allergic reaction to a food or drug.
Heat rashes are not often dangerous, but it is better to seek advice from a health-care professional if symptoms last for longer than a few days, in case the rash is more serious.
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