What is heat rash?

If you experience a heat rash and it goes away after showering and thoroughly drying your skin, you may not need to see a doctor.
If you experience a heat rash and it goes away after showering and thoroughly drying your skin, you may not need to see a doctor.

If you live in a hot and humid climate or have vacationed in one, you know that you can sweat a lot. Sweating is the body’s mechanism for cooling down — as sweat leaves the pores in the skin, it evaporates, taking body heat with it.

If your skin’s ducts become clogged, sweat can’t make it to the surface to evaporate. It becomes trapped and causes irritation. This is known as a heat rash or prickly heat

If you’re in a warm climate or plan to go to one, it’s essential to know what causes heat rash so that you can prevent it. Equally important are the signs of heat rash so that you can treat it or see the doctor and help them diagnose it to get proper treatment.

There are four prickly heat types, which are classified by how deep the pore blockage is:

Miliaria crystallina is the mildest and most common form of heat rash. It occurs when pores become clogged on the top layer of skin. Miliaria rubra is the form of heat rash that causes the prickling sensation known as prickly heat. 

If Miliaria rubra becomes infected or the tissue becomes inflamed, the bumps tend to fill with pus. This is known as miliaria pustulosa.

If your pores are clogged deep enough to affect the dermis, lesions can form that closely resemble goosebumps. If this is your condition's cause, you have miliaria profunda, the least common form of heat rash.

Main symptoms

Heat rash commonly shows up as a red rash in the affected area. Not everyone experiences the same heat rash symptoms. It may also present as:

Main causes

Your skin has three types of glands that secrete sweat — the eccrine, apocrine, and apoeccrine glands. Of these three, eccrine glands produce the most sweat. Your pores can become clogged for a variety of reasons, which keeps the sweat from flowing correctly. 

The pores become blocked because of:

A keratin plug is a buildup of skin cells that combine with oil secreting through the pores in your skin. These plugs keep sweat from flowing out of the pores and cause irritation. Bacteria can get into your pores through damaged hair follicles and cause infections that can clog your pores and cause heat rash if it is combined with other causes.

Tight clothing can restrict airflow and keep sweat against your skin. Tight clothes trap sweat, which can clog your pores and lead to a heat rash. If you sweat excessively (hyperhidrosis), you are more prone to heat rash — especially if you wear tight clothing or sweat for long periods.

Some medicated patches can cause prickly heat because they stick to or leave residue on the skin. 

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Diagnosis for heat rash

If you have a heat rash for a long time, or if it keeps coming back, see your doctor. They will talk to you about your symptoms and conduct a physical exam. This exam will include a close examination of your skin.

Treatments for heat rash

If you experience a heat rash and it goes away after showering and thoroughly drying your skin, you may not need to see a doctor. Home remedies for heat rash often work without a doctor.

Doctors usually treat heat rash with a combination of medication and actions you can take at home to treat it. Home remedies are generally enough to keep the condition from occurring, but if you’re an active and outdoors type, you might need some help.

Medication

In some cases, topical steroids may be necessary to reduce any inflamed tissue that has resulted from the rash. If the itching is severe, your doctor can prescribe calamine lotion to keep it under control and make it more bearable until the rash goes away.

If your heat rash is caused by skin cells collecting in your pores (keratin plugs), your doctor might give you some anhydrous lanolin ointment. This medicinal lotion helps dead skin cells fall off of the skin and keeps the skin hydrated.

Home remedies

Many people can treat prickly heat at home. If you have a rash after being out in the heat and sweating, take a hot shower and use a mild antibacterial soap. Dry thoroughly and put on loose clothing. Prickly heat should subside within a few days. Often, it goes away as soon as you are dry.

If the home remedy doesn’t work, or you keep getting a heat rash, take a picture of the rash for your doctor to see. You might have other skin conditions that are causing your prickly heat and will need to diagnose any conditions further.

Possible complications and side effects

If your heat rash is recurring, you can’t get rid of it, or you don’t treat it, it can turn into infections within your pores. Infections can lead to more severe conditions, so it’s essential to see your doctor if your heat rash doesn’t go away following the home treatments.

You may develop staph infection, have trouble regulating your body heat, or develop hyperhidrosis in unaffected areas.

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Medically Reviewed on 1/29/2021
References
Cedars-Sinai: “Prickly Heat."

DermNet NZ: “Miliaria."

John Hopkins Medicine: "Prickly Heat."

Temperature, Medical Physiology and Beyond: "Physiology of sweat gland function: The roles of sweating and sweat composition in human health."

StatPearls: “Miliaria.”

University of Rochester Medical Center: "Prickly Heat."