What does heat rash look like?: Causes and treatment

Heat rash, also known as miliaria rubra, prickly heat, summer rash, or wildfire rash is common and can be uncomfortable.

It happens when a blockage of the sweat glands causes perspiration to be caught in the deeper layers of the skin. Inflammation, redness, and blister-like lesions can result.

People who are overweight, and those who sweat easily, are more likely to get prickly heat. Babies and children are more prone to it because their sweat glands are not fully developed.

Fast facts on heat rash

  • Blockage of the sweat glands is the primary cause.
  • Symptoms include red bumps on the surface of the skin.
  • The rash is often described as ‘prickly’.
  • Over-the-counter (OTC) topical antibacterials are a common treatment

Symptoms of heat rash

Symptoms include small red bumps, called papules, which may itch or cause an intense, prickling sensation. They can appear in different parts of the body at the same time.

The most common places for heat rash to occur are the face, neck, under the breasts, and under the scrotum. It can also appear in skin folds and in areas of the body that rub against clothing, such as the back, chest, and stomach. These are all places that tend to sweat more often.

A related condition, which may happen at the same time, is folliculitis. This occurs when hair follicles become plugged with foreign matter, such as dead skin cells and sebum, that can later become infected, also causing inflammation.

What does heat rash look like?

Close-up image of heat rash, red bumps (papules) on the skin
This is what heat rash looks like, small red bumps (papules) on the skin.

Heat rash is sometimes broken down into three types:

Miliaria crystalline – the most common form. Includes small clear (or white) bumps filled with fluid (sweat) on the surface of the skin. There is no itching or pain. This is more common in babies than adults.

Miliaria rubra – also called prickly heat, it is associated with red bumps on the skin, inflammation, and a lack of sweat in the affected area. It occurs in deeper layers of the skin and is therefore more uncomfortable. If the pumps progress and become pus-filled, it is referred to as miliaria pustulosa.

Miliaria profunda – least common form of heat rash. Occurs in the dermis – the deepest skin layer. It can recur and become chronic. Miliaria profunda produces relatively large, tough, flesh-colored bumps.

Causes of heat rash or prickly heat

Woman's face sweating excessively.
Heat rash occurs when sweat glands are blocked.

Heat rash, or miliaria, happens when the sweat gland ducts get plugged due to dead skin cells or bacteria, such as Staphylococcus epidermidis, a common bacterium that occurs on the skin and is also associated with acne.

If the bacteria get inside the plugged sweat glands, it can lead to inflammation that appears as a rash.

Anything that causes a person to sweat more can lead to miliaria. It is common in humid, tropical climates.

Long periods of bed rest, due to immobility, and illness, can make a patient sweat, especially if using an electric blanket and other warm bedding.

Wearing too much clothing in winter, or sitting too close to a fire or heater can induce a rash.

Certain medications make it more likely, for example, psychotropics, which affect mental functions or behavior, and can raise the body’s temperature.

Medications for Parkinson’s disease can inhibit perspiration, so they too, increase the risk.

Drugs that alter the fluid balance in the body, such as tranquilizers, diuretic medications, or water pills, increase the tendency to develop prickly heat symptoms.

Diagnosing heat rash

Heat rashes are not often dangerous, but it is better to seek advice from a doctor if symptoms last for longer than a few days, in case the rash is more serious.

There are a number of conditions that can cause a rash, because “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.

It is important to take note of other symptoms associated with the rash, such as fever, cough, runny nose, fatigue, enlarged lymph nodes, or muscle aches.

If any of these other symptoms do occur, they could be a sign of a more serious infection that needs immediate medical attention.

Treatment for heat rash

Rashes like prickly heat often heal without intervention. Dry, itchy skin may disappear after being treated for a few days with over-the-counter (OTC) preparations.

  • Topical antibacterials – for example, antibacterial soaps, may shorten the duration of symptoms, even if there are obvious signs of infection.
  • Keep cool – Patients should keep the skin cool, and try to prevent sweating. Staying in an air-conditioned environment, avoiding activities that cause sweating, wearing loose clothing, and taking frequent cool showers can help.
  • Anti-itch preparations – such as calamine or menthol, or camphor-based preparations can help, as can topical steroid creams; it is important to use oil-based preparations with care because they can block the sweat glands further, encouraging the rash to persist.
  • Powder talc admixture – that contains the drying milk protein, labilin, and triclosan, an antibacterial, can be used to prevent infection. The powder stays on the skin and treats bacteria dispersed into bed linens, providing a reasonably dry refuge area for healing.
  • Cooling menthols – may make it easier to get to sleep.

Severe cases can last for several weeks and may cause significant disability. This may lead to an inability to sweat in response to heat. Secondary infections may occur, leading to abscesses.

If the rash develops into open blisters or pustular lesions, a doctor should be consulted. This may need more aggressive, medically monitored treatment.


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