Heat Rash: Symptoms, Types, Causes & How to Treat It
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
At a Glance
TL;DR: Heat rash — also called prickly heat or miliaria — happens when sweat is trapped in the skin because a sweat duct gets blocked. It isn't just a baby problem: adults get it too, especially in hot, humid conditions, often in skin folds or where clothing rubs. There are four types, from the mildest clear-bump form (crystallina) to the deeper, painful goose-bump-like form (profunda). The good news is that it usually heals on its own once the skin cools down — no tests are needed for diagnosis, just a skin exam. Cooling the skin, wearing loose clothing, and using a lanolin-based moisturizer help it clear faster, while oily or greasy products can make it worse.
Quick Answer:
What is it? A skin condition that occurs when sweat is trapped beneath the skin by a blocked or inflamed sweat duct; also known as prickly heat or miliaria.
Who gets it? Both adults and babies, especially in hot, humid conditions.
Where does it appear? Adults: skin folds and where clothing rubs. Babies: neck, shoulders, and chest (also armpits, elbow creases, groin).
How many types? Four — crystallina (clear bumps, mildest), rubra (“prickly heat”), pustulosa (pus-filled), and profunda (deep, less common).
How is it diagnosed? No tests needed — a provider usually diagnoses it just by examining the skin.
How is it treated? Cooling the skin and avoiding heat; mild heat rash tends to clear quickly once the skin is cool.
When should you see a doctor? If the rash lasts more than a few days, gets worse, or is more severe.
Note: This article reflects current clinical information as of its sources' last review (May 2022).
What Is Heat Rash?
Heat rash — also known as prickly heat and miliaria — isn't just for babies. It affects adults, too, especially in hot, humid conditions.
Heat rash occurs when sweat is trapped in the skin. Symptoms can range from small blisters to deep, inflamed lumps. Some forms of heat rash are very itchy.
The condition usually goes away once the skin cools down. Severe forms might need treatment from a healthcare provider.
Why Does Sweat Get Trapped?
Heat rash develops when a duct that leads from a sweat gland to the surface of the skin is blocked or inflamed. This then blocks the opening of the sweat duct on the surface of the skin, called the sweat pore.
Instead of evaporating, sweat is trapped beneath the skin, causing irritation and bumps on the skin.
Two kinds of sweat glands play a role in how your body sweats. Eccrine sweat glands occur over most of the body and open directly onto the skin's surface. Apocrine glands open into the hair follicle, leading to the surface of the skin, and develop in areas with many hair follicles, such as the scalp, armpits, and groin.
The 4 Types of Heat Rash
The types of heat rash are classified according to how deep the sweat is trapped in the skin. Signs and symptoms for each type vary:
Type | How Deep? | What It Looks and Feels Like |
Miliaria crystallina | Surface (mildest form) | When the opening of the sweat duct (sweat pore) is blocked, tiny, clear, fluid-filled bumps appear that break easily |
Miliaria rubra | Deeper in the skin | Also called prickly heat; small, inflamed blister-like bumps with itching or prickling in the affected area |
Miliaria pustulosa | Deeper (variant of rubra) | The inflamed bumps of miliaria rubra fill with pus |
Miliaria profunda | Deepest layer (dermis); less common | Firm, painful or itchy inflamed bumps that look like goose bumps and may break open |
Figure 2: Where heat rash shows up on adults and babies, the four types of miliaria, and the five main risk factors.
Where Does Heat Rash Appear?
The location depends on age:
Who | Where It Shows Up |
Adults | Usually in skin folds and where clothing rubs against the skin |
Infants | Mainly on the neck, shoulders, and chest; can also appear in the armpits, elbow creases, and groin |
What Are the Risk Factors?
Factors that increase the risk of heat rash include:
Risk Factor | Why It Raises Risk |
Newborn age | Sweat ducts are still immature and block more easily |
Hot, humid climate | Heavy sweating increases the chance of ducts getting blocked |
Physical activity | More sweat production means more opportunity for trapping |
Long bedrest with fever | Fever-driven sweating combined with lying still traps heat against the skin |
What Are the Possible Complications?
Heat rash usually heals without scarring.
There are two complications worth knowing about. People with brown or Black skin are at risk of spots of skin that get lighter or darker in response to inflammatory skin conditions — called postinflammatory hypopigmentation (lighter spots) or hyperpigmentation (darker spots). These changes usually go away within weeks or months.
A common complication is infection with bacteria, causing inflamed and itchy pustules.
When to See a Doctor
Heat rash usually heals by cooling the skin and avoiding exposure to the heat that caused it. See your healthcare provider if you or your child has symptoms that last longer than a few days or the rash seems to be getting worse.
Situation | What to Do |
Rash appears and you can cool the skin | Try self care first — most cases clear quickly |
Rash lasts longer than a few days | See your healthcare provider |
Rash seems to be getting worse | See your healthcare provider |
Rash is more severe | See a primary care provider or a skin specialist (dermatologist) to confirm it's heat rash and not another skin disorder |
How Is Heat Rash Diagnosed?
You don't need tests to diagnose heat rash. Your healthcare provider is usually able to diagnose it by examining the skin.
One condition can look like heat rash. Transient neonatal pustular melanosis (TNPM) mainly affects newborns with brown or Black skin. It is harmless and clears up in a couple of days without treatment.
How Is Heat Rash Treated?
Treatment for mild heat rash is cooling the skin and avoiding exposure to the heat that caused the condition. Once the skin is cool, mild heat rash tends to clear quickly.
Self-Care Tips
Tips to help your heat rash heal and to be more comfortable include:
Press a cool cloth on your skin or take a cool shower or bath. It may help to let your skin air-dry.
Avoid oily or greasy products — moisturizers, cosmetics, sunscreens, and other products that can block pores further. Instead, use a moisturizer with wool fat (anhydrous lanolin), which helps prevent sweat ducts from getting clogged.
Figure 3: The care pathway — from noticing the rash, to self care at home, to when to see a provider — plus hot-weather prevention steps and two side notes about medicines and bacterial infection.
How Can You Prevent Heat Rash?
To help protect yourself or your child from heat rash:
Prevention Step | What to Do |
Dress for the heat | In hot weather, wear loose, lightweight clothing that wicks moisture away from the skin. Don't wrap newborns in too many layers |
Limit heat exposure | In hot weather, limit physical activity. Stay in the shade or in an air-conditioned building, or use a fan to circulate the air |
Cool your sleeping area | Keep your sleeping area cool and well ventilated |
Choose skin products carefully | Avoid creams and ointments that can block pores |
Review your medicines | Avoid drugs that cause sweating, such as clonidine, beta blockers, and opioids |
Preparing for Your Appointment
A visit with a healthcare provider usually isn't necessary for heat rash. If your rash is more severe, you may want to see your primary care provider or a doctor who specializes in skin disorders — a dermatologist — to be sure it's heat rash and not another skin disorder.
Before you go, it's a good idea to list questions you have about your condition. For heat rash, questions to ask your healthcare provider include:
Questions to Ask Your Provider |
What could have caused this rash? |
How can I treat it? |
Do I need to limit physical activity until the rash clears? |
How can I prevent it in the future? |
Conclusion and Next Steps
Heat rash looks alarming — clusters of red bumps or clear fluid-filled blisters can make anyone worry. But the mechanism is simple: a blocked sweat duct traps sweat under the skin, and the skin responds with bumps. The fix is just as straightforward: cool the skin, get out of the heat, and let it heal.
Most cases clear quickly with no treatment at all. Reach for a cool cloth, a cool shower, and a lanolin-based moisturizer instead of anything oily or greasy. Dress in loose, breathable clothing, keep your sleeping area ventilated, and keep babies from being over-wrapped in hot weather.
Call to action: If your rash lasts more than a few days, keeps getting worse, or looks more severe than a typical summer rash, book a visit with your provider — or a dermatologist for a definitive check that it's heat rash and not something else. Bring your medication list, since clonidine, beta blockers, and opioids can increase sweating and raise your risk.
Frequently Asked Questions
What is the difference between heat rash and prickly heat?
There is no difference. Prickly heat is simply another name for heat rash (miliaria rubra specifically), describing the itching or prickling sensation that comes with the inflamed blister-like bumps.
Does heat rash go away on its own?
Yes, usually. Heat rash typically heals by cooling the skin and avoiding the heat that caused it, and mild heat rash tends to clear quickly once the skin is cool.
How long does heat rash last?
Most cases clear within a few days of cooling the skin. See a provider if symptoms last longer than a few days or the rash seems to be getting worse.
Is heat rash contagious?
No. Heat rash is caused by blocked sweat ducts trapping sweat under the skin — it cannot spread from person to person.
Can heat rash get infected?
Yes. A common complication is infection with bacteria, which causes inflamed and itchy pustules. Providers can treat this if it occurs.
What should I avoid when I have heat rash?
Avoid oily or greasy moisturizers, cosmetics, and sunscreens that can block pores further. Avoid creams and ointments that block pores, and avoid the heat and activity that caused the rash.
What is the best moisturizer for heat rash?
A moisturizer containing wool fat (anhydrous lanolin) helps prevent sweat ducts from getting clogged, unlike oily or greasy products that can block pores further.
Why do newborns get heat rash?
Newborns are at higher risk because their sweat ducts are immature and block more easily. Avoid wrapping babies in too many layers in hot weather.
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References
Heat rash: Symptoms & causes. mayoclinic.org
Heat rash: Diagnosis & treatment. mayoclinic.org
Disclaimer: This article is for general educational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. Always seek the guidance of your healthcare professional with any questions about a medical condition. In a medical emergency, call 911 or your local emergency number.
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