Why do I have heat rash on my buttocks, and what should I do?

A heat rash on the buttocks has nothing to do with acne or folliculitis. In this case, it’s not the hair follicle that becomes inflamed—it’s the duct of a sweat gland that becomes blocked. Sweat becomes trapped beneath the skin’s surface, causing a rash of small red lesions accompanied by an unpleasant tingling sensation. The cause is mechanical, not bacterial. This condition is known as miliaria, or “prickly heat” in babies.

The good news: It usually goes away within a few days once the skin is exposed to air and feels refreshed. The bad news: most standard skincare routines—especially rich creams—make the problem worse instead of soothing it. Even a purifying diaper rash cream has its place in your routine once the flare-up has passed, but not while it’s still active: if applied too early, it won’t have any effect and may even irritate the skin. Here’s how to recognize heat rash, treat it, and prevent it from coming back.

What exactly is a heat button?

The skin releases heat by producing sweat, which is carried to the surface through tiny channels. When it is hot and humid, sweating is excessive, and nothing evaporates, these channels become blocked. Sweat accumulates beneath the skin’s surface, causing maceration and triggering a local inflammatory reaction due to this trapped moisture. This condition is known as miliaria, more commonly called heat rash.

It takes three forms. The most superficial form produces tiny, translucent blisters—without redness or pain—that burst at the slightest touch. The most common form, which affects the buttocks, results in small red papules accompanied by a tingling sensation and sometimes itching. The deep form, which is rarer, tends to appear in adults after repeated episodes and produces flesh-colored lesions that do not itch. In all cases, the cause is the same: trapped moisture and zero evaporation.

How to Recognize a Heat Rash

This is the key question, because the approach differs completely depending on the answer. The factors that help determine the answer:

• The lesions are numerous, tiny, and all identical, distributed evenly across the area. Folliculitis, on the other hand, causes pimples of varying sizes, each centered around a hair.
• The predominant sensation is a tingling or mild burning sensation, not deep pain. A buttock boil, on the other hand, is genuinely painful—so much so that it makes it impossible to sit down—so there’s no mistaking it.
• There are no pus, whiteheads, or blackheads. Comedones and pores clogged with sebum are symptoms of acne, a different type of condition that is more common in acne-prone skin.
• The symptoms appear suddenly, within a few hours, after exposure to heat, a workout, a long trip in tight jeans, or a day spent in a wet swimsuit.
• The rash disappears quickly once the area is cooled. The lesions appear quickly and fade quickly: irritation that lasts longer than a week is probably not heat rash.

If the bumps persist, and if they’re rough and dry rather than red, it could be keratosis pilaris. If they’re centered around a hair after hair removal, check for ingrown hairs. And for blemishes caused by sebum, see the sections on body acne and back acne.

Why the buttocks Are a High-Risk Area

• Prolonged sitting presses the skin against a seat and prevents evaporation: this is the primary factor.
• Tight-fitting clothing and synthetic fabrics trap moisture against the skin. Summer jeans are a classic example.
• Constant friction from the fabric damages the hydrolipidic film and can contribute to the development of pimples in the areas where the fabric comes into contact with the skin.
• Leaving a swimsuit on while it's still wet after swimming creates an ideal warm, humid environment.
• Excessive sweating—whether caused by exercise, a fever, or simply the summer heat—clogs the sweat ducts.
• Thick creams and oils applied to the area further clog the pores. To understand the underlying mechanism, see where sweat comes from.

What to Do When It Appears

The principle can be summed up in one word: cooling. Everything else follows from that.

• Refresh the area. Take a lukewarm or cool shower, then pat the skin completely dry. A spritz of thermal water soothes the tingling sensation.
• Let your skin breathe. Wear loose-fitting cotton clothing, avoid synthetic underwear, and spend as little time as possible sitting on the affected area.
• Clean with a mild soap or a fragrance-free cleansing cream. Gentle cleaning is sufficient—no need to scrub.
• Avoid rich creams, thick oils, and occlusive balms, which can make the blockage worse. A light, soothing aloe vera gel—or any soothing, non-occlusive formula—is best; otherwise, use nothing at all.
• Do not scratch or pierce the lesions: they are fragile, and a secondary bacterial infection would worsen the developing infection and turn a minor problem into a painful lesion that requires treatment.
• Wait. Within two to five days in a cool place, the rash will go away on its own, without treatment.

Once the breakout has subsided, your skin may remain dry or slightly irritated. This is when moisturizing comes back into play—with a lightweight, non-comedogenic moisturizer rather than a rich formula: a serum or a lightweight emulsion helps your skin shed dead skin cells and restore a healthy barrier. This is the time to moisturize—not before. Exfoliating ingredients like salicylic acid, a gentle scrub, or a treatment for blemishes should only be reintroduced afterward—never during a breakout. And if you’re spending time in the sun, apply a non-greasy sunscreen to exposed areas.

In Infants and Children

Heat rash is very common in infants, whose sweat glands are still underdeveloped. It’s called “prickly heat.” It appears on the neck, back, forehead, and bottom, often as a result of wearing too many layers or being in an overheated room. The solution is simple, and this is the basic advice: remove a layer of clothing, aim for a room temperature of 19 °C, opt for cotton, give the baby a lukewarm bath, and dry the skin folds thoroughly. This is a natural, chemical-free tip that’s essential at this age.

Be careful not to confuse this with diaper rash, which is caused by moisture in the diaper and prolonged contact with urine: diaper rash is treated with frequent diaper changes and a protective ointment. If you have any doubts, or if the rash spreads, oozes, or is accompanied by a fever, consult your pediatrician.

When to See a Doctor or Dermatologist

A heat rash does not normally require a doctor’s visit. Seek medical advice if the rash lasts more than a week despite applying a cool compress, if the lesions become painful, if pus appears, if you have a fever or swollen lymph nodes, if the affected area spreads rapidly, or if you have diabetes, a weakened immune system, or are taking medication that suppresses your immune system. These situations suggest a secondary infection, and antibiotic treatment should be prescribed following a clinical examination—never self-administered.

It is also helpful to consult a dermatologist in cases of recurring flare-ups, when deep miliaria develops in adults, or to rule out other skin conditions: eczema, mycosis, or fungal infections can sometimes present with similar symptoms that only a professional diagnosis can distinguish.

Preventing Heat Rash

• Choose cotton and breathable fabrics, and avoid tight-fitting clothes in the summer.
• Change clothes immediately after exercising or swimming, without letting your swimsuit dry on you.
• Get up regularly when working in a seated position, and avoid prolonged exposure to hot surfaces.
• Refresh your skin throughout the day with a quick shower or a spritz of water.
• Simplify your routine in hot weather: opt for lightweight, fluid textures rather than balms, both on your body and face. Avoid using essential oils on skin experiencing a flare-up.
• Maintain a gentle daily skincare routine and use a light moisturizer to keep your skin healthy without clogging your pores.

For ongoing care—not just as a quick fix—a body treatment for blemishes like Fesse Time, our best-selling lactic acid product suitable for ages 3 and up, smooths the skin texture on the buttocks, back, and arms. The complete routine is detailed in the guide to getting rid of pimples on the buttocks. Check it out on our website or at retail locations, with free shipping on orders of €50 or more.

FAQ

This article is published for informational purposes only; it is not a substitute for medical advice.