Heat rash, sometimes called prickly heat, sweat rash, or miliaria, is a skin condition that develops when the sweat gland ducts become inflamed or blocked.
It often appears on areas of the body where people experience friction: the skin folds of the neck, underarms, groin, shoulders, chest, and elbow creases.
People who wear tight clothing, engage in intense physical activity, or live in a hot environment are most likely to experience heat rash.
Heat rash can affect both children and adults. Researchers believe children and infants may be especially prone to the condition because their immature sweat glands don’t always efficiently eliminate the sweat they produce.
Heat rash can look and feel uncomfortable, but it is not contagious.
Most cases of heat rash clear up as soon as patients remove themselves from the high-temperature situation and allow their skin to cool off.
In rare cases, when heat rash is more severe, a healthcare provider will recommend ointments, creams, or other rash treatments to help soothe symptoms and relieve discomfort.
In this article, I’ll tell you more about what heat rash is, including its symptoms and causes. I’ll also talk about how it can be treated and prevented.
What is Heat Rash?
Heat rash is a common skin condition that occurs when sweat gland ducts are inflamed or blocked, trapping sweat and causing it to flow back under and into the skin.
When this happens, sweat becomes channeled into a rash of fluid-filled sacs, bumps, or blisters that appear on the surface of the skin on and around the affected area.
People can develop different types of heat rash:
- Miliaria crystallina: The mildest form of heat rash, miliaria crystallina, affects sweat gland ducts near the top or surface of the skin. People with miliaria crystallina develop clear or white fluid-filled bumps that rupture easily with light pressure.
- Miliaria rubra: Sometimes called prickly heat or prickly heat rash, miliaria rubra appears when sweat gets channeled into deeper layers of the skin. Symptoms include skin itchiness, an uncomfortable prickling sensation, and a rash of several small bumps. The rash may be light to dark red depending on the skin tone and type.
- Miliaria pustulosa: Occasionally, a patient with miliaria rubra can develop a secondary bacterial infection inside their skin rash. Pustules, pockets of skin filled with pus, can form. When this happens, the condition is called miliaria pustulosa.
- Miliaria profunda: The rarest and most severe form of heat rash, miliaria profunda, occurs when sweat gets trapped in the deepest layer of the skin, resulting in large, firm, flesh-colored bumps that appear on the skin’s surface. Research suggests that individuals who have miliaria profunda have a history of experiencing episodes of miliaria rubra or who are brand-new to humid, tropical climates.
Some skin conditions share symptoms with heat rash. If you are experiencing abnormal skin irritation and aren’t sure what may be causing your symptoms, contact a healthcare provider.
Symptoms of Heat Rash
Heat rash can affect individuals of any age, race, or gender, but some people are more vulnerable to developing symptoms than others.
People who live in a hot, humid climate or experience very hot weather during the summer are most likely to develop heat rash.
Likewise, those who wear tight clothes or engage in strenuous physical activity in warm weather can develop symptoms.
Patients on bed rest, including pregnant women, are also at high risk for heat rash.
Heat rash in adults
Adults experience heat rash symptoms that can range from mild to severe, including:
- Skin irritation
- Skin inflammation or swelling
- Clear, white, or red bumps
- Small blisters
- Raised welts or lumps
- An itchy or prickly feeling
Typically, adults with heat rash will see their symptoms develop in areas that sweat or experience friction.
The underarms , insides of the elbows, groin, inner thighs and the area under the breasts are all susceptible to heat rash.
If you believe you have heat rash and begin to experience additional symptoms such as a fever, chills, increasing pain, or if you start to see pus draining from the rash area or notice other signs of infection, you may require medical attention.
Make an appointment to see a primary care provider or dermatologist to ensure you have the proper diagnosis and treatment plan.
Heat rash in infants
It is very common for infants and babies to develop heat rash because their sweat glands have not yet fully developed. Symptoms include:
- Clusters of red bumps, blisters, or pimples
- Tiny water- or fluid-filled blisters
- Raised red bumps that feel moist to the touch
Heat rash in infants can appear on the face, shoulders, and upper chest. It is also likely to develop in the skin folds of the neck, elbow, knees, and diaper area.
You can treat your infant’s heat rash at home to relieve itchiness and soothe the rash.
However, if your baby’s skin does not resolve in two to three days, or if they develop a fever, chills, or other symptoms, or if the rash gets worse, call a healthcare provider or go to the nearest healthcare facility to seek medical care.
Causes of Heat Rash
Heat rash happens when an individual is exposed to too much heat and their sweat glands cannot efficiently manage the perspiration that is needed to cool their body.
When this happens, sweat backs up and begins to be channeled into the skin, leading to an itchy rash and other symptoms.
Underdeveloped sweat ducts
From the time they are newborn babies until they reach around two years of age, children have underdeveloped sweat ducts that cannot adequately regulate body temperature.
If young children are bundled up too warmly, spend too much time outside on hot days, or are exposed to too much sun, too much heat, or too much humidity, their bodies can have trouble keeping their skin cool.
As a result, they are considered highly vulnerable to heat rash and other serious heat-related illnesses like heat exhaustion, heatstroke, and heat cramps.
If your child shows signs of overheating, including vomiting, extreme drowsiness, rapid heartbeat, not eating or drinking, uncontrollable crying, a body temperature above 102° degrees Fahrenheit or red, hot, dry skin, they may require emergency medical care.
Take immediate steps to gradually cool them down and seek medical attention as quickly as possible.
People who live in humid, tropical climates or experience hot weather are more prone to developing heat rash than others. Warm weather causes frequent perspiration.
This can contribute to sweat glands clogging and sweat being trapped under the skin.
Individuals who participate in strenuous exercise or rigorous outdoor activity, particularly in warm weather, are at high risk of developing heat rash.
Being physically active can trigger excessive sweating. When the body can’t efficiently channel the sweat produced, a heat rash may form.
Patients on bed rest for medical reasons, including pregnant women, immobilized patients, and the elderly, can develop heat rash if they lay in one position for too long.
Lying against a surface can block sweat glands, causing a backflow of sweat into the skin.
Heat Rash Treatment
If you or your child’s skin feels prickly, irritated, or showing other signs of heat rash, there are steps you can take at home to help soothe your symptoms and relieve your discomfort.
If your heat rash is bothersome after cooling the skin, you can use topical treatments to alleviate your symptoms and discourage complications such as bacteria formation.
- Anhydrous lanolin ointment or balm: Over-the-counter anhydrous lanolin products can be used as a moisturizer and barrier, protecting the affected area and preventing new bumps from forming. A very light layer can be applied to the rash area.
- Topical anti-inflammatories: Available over-the-counter medications, such as hydrocortisone cream, can be used to treat inflammation and relieve other symptoms related to heat rash. The cream should not be applied to open skin. Discontinue the cream if there is any worsening or the rash has not resolved in 2-3 days.
- Prescription medications: If your heat rash is severe, a healthcare provider may prescribe other topical medications such as antibiotic or steroid creams.
Tight, synthetic fabrics can trap body heat and worsen heat rash symptoms, particularly if people wear them during warm weather or other conditions involving excessive sweating.
If you have a heat rash, dress in loose-fitting clothing made from natural materials like cotton, linen, or silk.
These loose, breathable fabrics will allow air to circulate near your body and keep you cool.
Taking a shower with cool water or a cool bath is one of the best ways to bring your body temperature down and keep heat rash from worsening. The water should be cool but not cold.
After you are finished bathing, allow your skin to air dry rather than toweling off to avoid blocking skin pores or exacerbating symptoms.
Use non-drying soap
Washing with a non-drying soap can help skin stay moisturized and healthy.
Use a soap that does not contain fragrances or dyes, as those additives can cause skin condition symptoms to flare.
Using cool compresses is one of the best ways to treat heat rash and find quick relief.
Begin by rinsing a clean washcloth in cool water, and then squeeze out excess liquid. Next, apply the cool compress directly to your skin to reduce pain and inflammation.
Heat Rash Prevention
It’s not always possible to avoid heat rash, but there are steps you can take to decrease your risk of developing symptoms.
Take precautionary measures during hot or humid weather, including:
- Staying in air-conditioned, shady, or cool areas when possible
- Drinking water and avoiding dehydration
- Wearing loose-fitting, light clothing made from breathable fabrics
- Reduce physical exertion or exercise during the hottest times of the day
- Take cool showers and baths regularly
- Carry a portable fan or water mister to help cool you on the go
If you want to keep your children from experiencing heat rash, make sure that you keep them cool, hydrated, and out of the sun.
In addition, they should be dressed comfortably in light, loose-fitting clothing and should always have a clean, dry diaper.
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Frequently Asked Questions
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.
K Health has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references.
Frequently Asked Questions (FAQ) About Extreme Heat (2012).
Heat Rash (prickly heat). (2021).
Newborn Skin: Common Skin Problems. (2017).
Thermoregulatory responses of children exercising in a hot environment. (2013).