Prickly heat is a skin rash that happens when sweat gets trapped beneath the surface of your skin. Sweat ducts become blocked, and instead of evaporating normally, moisture builds up under the skin and forms small bumps that can itch, sting, or burn. The rash typically clears up on its own within a few days once you cool down, but in some cases it can lead to complications worth knowing about.
How Sweat Gets Trapped
Your body has millions of sweat glands designed to release moisture onto the skin’s surface, where it evaporates and cools you down. In hot, humid conditions, or when clothing traps heat against the body, sweat ducts can become clogged with dead skin cells or bacteria. When that happens, sweat has nowhere to go. It leaks into the surrounding skin tissue instead of reaching the surface, triggering inflammation and those characteristic tiny bumps.
The depth of the blockage determines how the rash looks and feels. There are three main forms, each progressively deeper in the skin:
- Crystallina (superficial): The mildest type. Sweat is trapped just below the outermost layer of skin, producing tiny, clear, fluid-filled blisters that break easily. There’s usually no itching or pain, and these resolve fastest.
- Rubra (mid-level): The classic “prickly heat.” The blockage occurs deeper, causing small red bumps with an itching or stinging sensation. This is the most common form people notice and search for.
- Profunda (deep): The rarest form. Sweat is trapped in the deeper layers of skin, producing firm, flesh-colored bumps. Because sweat can’t reach the surface at all in affected areas, the skin there stops sweating entirely.
What It Looks and Feels Like
Prickly heat shows up as clusters of small bumps, typically in areas where skin folds or clothing creates friction: the neck, chest, groin, armpits, inner elbows, and back. In the rubra form, the bumps are red and surrounded by irritated skin. You may feel a prickling or burning sensation, especially when you start sweating again. Some people describe it as feeling like tiny needles pressing into the skin, which is where the name comes from.
The rash can look similar to other skin conditions, so it helps to know what sets it apart. Unlike eczema, which is a chronic immune-driven condition that causes dry, scaly, cracked skin, prickly heat produces fluid-filled bumps in sweaty areas and is directly tied to heat exposure. Eczema tends to flare in response to allergens, stress, or dry air, while prickly heat follows a clear pattern: you got hot, you sweated, and the rash appeared. Unlike hives, which produce raised welts that can appear anywhere and shift location within hours, prickly heat bumps stay put in the areas where sweating was heaviest.
Who Gets It
Anyone can develop prickly heat, but certain groups are more vulnerable. Newborns and infants are especially prone because their sweat glands are still developing and clog more easily. Overdressing a baby or swaddling in warm environments is a common trigger. Adults who move to tropical climates, exercise heavily in humidity, or are on bed rest with a fever also face higher risk. People who are overweight may be more susceptible because of increased skin-on-skin contact in folds where heat and moisture accumulate.
How to Treat It
The most effective treatment is also the simplest: cool down. Get out of the heat, move to an air-conditioned space, take a cool shower, or apply cool compresses to the affected skin. In most cases, the rash resolves on its own within a few days once the skin dries and the sweat ducts unblock.
While the rash is active, you generally want to keep your pores open, which means avoiding heavy creams and ointments that could make the blockage worse. If the itching is intense, calamine lotion can help. Beyond that, keeping the skin dry and exposed to air does most of the work. Resist the urge to scratch, since broken skin in a warm, moist environment is an invitation for bacteria.
Preventing Flare-Ups
Clothing choices matter more than most people realize. Synthetic fabrics trap heat against the skin, even moisture-wicking athletic wear, which can fit too tightly and press against sweat ducts. Light, loose-fitting cotton is a better option because it allows airflow across the skin’s surface. If you develop a heat rash around your groin, skipping undergarments until it clears can speed recovery.
Beyond clothing, the basics are straightforward: stay in cool environments when possible, use fans or air conditioning during heat waves, shower after sweating, and pat skin dry rather than rubbing. If you know you’re prone to prickly heat, limit time spent in hot, humid conditions and take breaks in cooler spaces throughout the day.
When Prickly Heat Becomes Serious
Most prickly heat is a nuisance, not a danger. But two complications are worth watching for.
The first is bacterial infection. When the inflamed bumps fill with pus instead of clear fluid, bacteria have likely moved in. This can progress to deeper skin infections or abscesses if left untreated. Signs to look for include increasing pain, swelling, warmth around the bumps, pus drainage, or fever. Infected prickly heat typically needs topical antibiotics to clear.
The second is overheating. In both the rubra and profunda forms, the blocked sweat glands stop functioning in the affected areas. If the rash is widespread enough, your body loses a significant portion of its cooling ability. This can lead to heat exhaustion or heat stroke, particularly in people exercising or working outdoors. A spreading heat rash combined with dizziness, rapid heartbeat, or a body temperature that keeps climbing is a medical concern, not just a skin issue.
If a rash you think is prickly heat doesn’t improve within a few days of cooling down, it’s worth having it evaluated. Several other skin conditions can mimic prickly heat, and a persistent rash may be something else entirely.