What to Know About Heat Rash
- Heat rash is a term for a number of skin problems that arise or worsen because of heat exposure or overheating.
- Common names for heat rash include prickly heat or miliaria
- Heat rash is caused by exposure to a hot environment.
- Symptoms of heat rash are the appearance of a rash and itching.
- Heat rash is diagnosed by looking at skin changes and a history of exposure to heat.
- Treatments for heat rash include cleaning the area with water and mild soap and in more persistent cases a mild steroid cream (cortisone )
- Heat rash can be prevented by staying in cool areas and wearing loose clothing.
What Does Heat Rash Look Like? Pictures
The Four Types of Heat Rash
The four types of heat rash (miliaria) are named by the way they look on the skin (visual characteristics):
- Clear (miliaria cystallina)
- Red (miliaria rubra)
- White/yellow (miliaria pustulosa)
- Deep (miliaria profunda)
What Are the Symptoms of Heat Rash?
Heat rash usually appears as very small pinpoint bumps at the entrances to sweat glands. In some areas, there may be red or pink patches of skin. More advanced heat rash may have greater degrees of irritation and large welts and raised red bumps. Some people with heat rash are very itchy while others may have no irritating symptoms.
Any body part with sweat glands may be affected. Characteristic heat rash areas include the following:
- Under the breasts
- Elbow folds
What Are the Types of Heat Rash?
Clear (Miliaria Crystallina)
White/Yellow (Miliaria Pustulosa)
Miliaria is the medical term for heat-related skin conditions where tiny, pinpoint, and pink to clear bumps form over a body area like the face or neck. It is caused when small sweat droplets are trapped in the skin due to blocked pores. This trapping of sweat may cause inflammation and itching around the sweat pores. Miliaria is very common in infants but may also occur in adults. This condition occurs especially after repeated episodes of sweating in a hot, humid environment. Miliaria may look like small clear blisters or like gooseflesh.
There are four common types of miliaria:
- Clear (miliaria crystallina): Mildest form, usually the blisters aren't itchy or painful
- Red (miliaria rubra): Occur deeper in the outer skin layer and may be itchy with red bumps in infants and adults
- White/Yellow (Miliaria Pustulosa): When pustules form on a case of red heat rash it is called white/yellow heat rashand may be the first signs of a skin infection
- Deep (miliaria profunda): Least common form, usually occurs after repeated events of heat rash and causes flesh-colored lesions
What Causes Heat Rash?
Heat rash, or prickly heat, is thought to arise from plugging of sweat ducts and hair follicles on the skin. Occluded sweat glands with trapped sweat give rise to the tiny water bumps seen in this condition. Human sweat (with its high salt content) is a very potent skin irritant and may cause skin rashes. It is important to wash off sweat with gentle soap and water.
What Are the Risk Factors for Heat Rash?
Anyone can develop heat rash, especially in certain environments. Some individuals, however, are more prone to heat rash:
- Children under age 4
- Athletes or people who exercise in hot environments
- Obese or overweight persons
- Bedridden and non-ambulatory patients
- Individuals with congenital absence or decreased sweating
- Military troops
What Procedures and Tests Diagnose the Cause of Heat Rash?
Persistent heat rash is typically diagnosed from the characteristic skin appearance on the exam and a history of recent heat exposure.
Atypical or more resistant cases of heat rash may require skin culture, a microscopic exam from skin scrapings, or less commonly a skin biopsy (surgically removing a very small piece of skin using a local numbing agent. This skin is sent to a pathologist for closer examination.
Additional tests may be required to exclude other causes of skin rashes, for example:
What Are Home Remedies to Relieve Symptoms of Heat Rash?
Home remedies for treating heat rash include washing the affected area with mild soap and rinsing the area, then gently drying the area. Wear clothing that allows the skin to breathe in a hot environment. Stay hydrated and drink plenty of water to prevent dehydration in hot environments. Medical care may be necessary if the heat rash does not resolve with home remedies.
Most heat rash resolves without treatment, often within a day after changing to a cooler environment. The best way to prevent heat rash is to avoid sweating by staying in cooler areas, using fans, and limiting physical activity.
The following self-care steps and remedies may help with heat rash.
The first step in treating heat rash is to wash the affected area with a gentle soap (for example, Dove non-soap cleanser or something similar). Next, rinse the area with water and gently pat dry with a towel. It is recommended to wash several times a day, especially after exercise, prolonged walking, or heat exposure.
- Remain in a cool environment and allow for adequate ventilation of the skin.
- Take cool showers or baths
- Rest in an air-conditioned room at 70 F to 72 F (21 C to 22 C). If no air conditioning is available at home, safe retreats include indoor shopping malls, grocery stores, movie theaters, hotel lobbies, ice-skating rinks, bowling alleys, etc.
- Avoid skin-to-skin contact by placing a clean cotton washcloth or material between skin folds like under the breasts or abdomen.
- Apply cool packs over the affected areas (do not leave packs on longer than 20 minutes per hour).
- Mild cortisone creams like hydrocortisone (Cortaid) or prescription cortisone creams like triamcinolone (Triesence, Trivaris Intravitreal) may be helpful for resistant rashes or resulting eczema. If it is necessary, apply these creams twice daily. For large areas, you should contact your healthcare professional.
- Oral antihistamines, such as diphenhydramine (Benadryl), can help decrease itching, mostly through the sedation associated with these medications.
Getting naked may keep the body cooler but it does not avoid the problem of sweat buildup especially under the breasts, abdomen fold, between buttock folds, and places where skin overhangs. It may be best to wear light, cotton, absorbent fabrics that separate out skin fold areas. Individuals who do not wear underwear usually notice more retained sweat and therefore more irritation in areas between the buttocks and groin. Short sleeves tops and shorts are often helpful.
Drink plenty of water for overall hydration. Water can help maintain cooler body temperatures. Dehydration may lead to weakness and generalized malaise.
What Factors Aggravate Heat Rash?
- High humidity
- High temperatures
- Jacuzzi's, saunas, and steam rooms
- Regular sweating or hyperhidrosis (excess sweating)
- Tight garments and non-breathable fabrics
What Are the Complications of Heat Rash?
While heat rash does not lead to heat stroke, both conditions may rarely occur in the same individual. Heat rash is a very common, self-limited skin condition while heat stroke is an uncommon more serious, generalized illness. Heat stroke requires immediate medical attention. Heat stroke is particularly life-threatening in the frail, ill, and elderly.
What Conditions Mimic 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")
- Allergic Rash
- 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, this can cause a temporary overall body flushing and heat rash-like appearance that improves in a few hours)
When Should You Call a Doctor for Heat Rash?
If the rash is not improving or resolving with the home treatment described or becomes worse after several days, the patient should see a physician to be sure there is not a bacterial infection or other cause for the rash. If the rash is accompanied by other significant symptoms (dizziness, chest pain, shortness of breath, etc.) the person should seek medical care.
Seek medical care immediately if you have a heat rash with these symptoms:
Can Heat Rash Be Prevented?
How to Prevent Heat Rash
- Move to cooler environments, for example:
- Air conditioning or oscillating fans.
- Limit your physical activity in a hot environment.
- Wear cool breathable fabrics such as cotton.
- Avoid polyester and nylon clothing.
- Maintain a comfortable room temperature with fans and air conditioning.
- Babies and infants should be kept comfortably cool and dry. Because babies and infants have more fat folds, they frequently get rashes on their diaper area and abdomen folds (diaper rash).
- Infant drooling may cause further occlusion of sweat ducts and hair follicles leading to heat rash on the face and cheeks.
- Bedridden and wheelchair-bound people should be rotated and moved to avoid constant sweating and occlusion in the same area.
Heat Rash Dos
- Get out of the heat.
- Wear cool, breathable fabrics, for example, cotton.
- Maintain comfortable temperatures with fans and air conditioning.
- Wash off the skin with mild soap and pat dry after sweating or exercising.
- Take a cool shower or bath.
Heat Rash Don'ts
- Don't wear polyester and nylon fabrics in the summer.
- Don't cover with ointments, Vaseline, or heavy creams.
- Don't scrub or rub the skin to remove heat rash bumps.
- Don't stay in the heat or humidity.
- Don't go in a hot tub, sauna, or Jacuzzi.
Reviewed on 9/30/2022
Levin, NA, MD. Miliaria. Medscape. Updated: May 24, 2018.
Rakel RE, Rakel D. "Textbook of Family Medicine." 9th edition. 2015 Saunders.