Heat Rash (Prickly Heat): Complete Guide to Symptoms, Types, Causes, and Treatment
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
Heat Rash (Prickly Heat): Complete Guide to Symptoms, Types, Causes, and Treatment
TL;DR
Heat rash (prickly heat, miliaria) forms when a blocked or inflamed sweat duct traps sweat beneath the skin instead of letting it evaporate. It ranges from tiny clear bumps that don't itch (miliaria crystallina) to deep, painful, goosebump-like lumps (miliaria profunda). It is not just a baby problem — adults get it in skin folds and clothing friction areas. Mild heat rash usually clears quickly once the skin cools down. See a doctor if the rash lasts more than a few days or keeps worsening.
Quick Answer
Heat rash (also known as prickly heat and miliaria) occurs when sweat is trapped in the skin because a sweat duct leading to the skin's surface is blocked or inflamed. Instead of evaporating, sweat sits beneath the skin and causes irritation and bumps. The four types are classified by how deep the sweat is trapped: miliaria crystallina (mildest, clear bumps with no itch), miliaria rubra (itchy "prickly heat"), miliaria pustulosa (pus-filled bumps), and miliaria profunda (deep, firm, goosebump-like lumps). Treatment for mild heat rash is simply cooling the skin and avoiding the heat that caused it — the rash usually clears quickly. See a health care provider if symptoms last longer than a few days or the rash seems to be getting worse.
What Is Heat Rash?
Heat rash is a skin condition that occurs when sweat is trapped in the skin. It is also known as prickly heat and miliaria.
Heat rash is not just for babies. It affects adults too, especially in hot, humid conditions. Symptoms can range from small blisters to deep, inflamed lumps, and some forms are very itchy.
The good news: heat rash usually goes away once the skin cools down. Severe forms of the condition might need treatment from a health care provider.
How Trapped Sweat Causes Heat Rash
Your skin is full of sweat glands whose ducts lead to the surface. The most common type, the eccrine sweat gland, occurs over most of the body and opens directly onto the skin's surface through a tiny opening called a sweat pore. A second type, the apocrine gland, opens into the hair follicle and is found in areas with many hair follicles, such as the scalp, armpits, and groin.
Heat rash develops when a duct that leads from a sweat gland to the surface of the skin becomes blocked or inflamed. This blocks the opening of the sweat duct on the surface of the skin — the sweat pore. Instead of evaporating, sweat is trapped beneath the skin, causing irritation and bumps on the skin.
Where Does Heat Rash Appear?
Location depends on age. Adults usually develop heat rash in skin folds and where clothing rubs against the skin. In infants, the rash is mainly found on the neck, shoulders, and chest. It can also show up in the armpits, elbow creases, and groin.
| Age group | Where heat rash typically appears | | --- | --- | | Adults | Skin folds; areas where clothing rubs against the skin | | Infants | Neck, shoulders, chest; also armpits, elbow creases, groin |
The Four 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 | Depth | What it looks like | How it feels | | --- | --- | --- | --- | | Miliaria crystallina | Most superficial — blocked sweat pore at the skin surface | Tiny, clear, fluid-filled bumps that break easily | Does not hurt or itch | | Miliaria rubra ("prickly heat") | Deeper in the skin | Clusters of small, inflamed blister-like bumps | Itching or prickling in the affected area | | Miliaria pustulosa | Same depth as miliaria rubra | Inflamed bumps filled with pus | Itchy; a variant of miliaria rubra | | Miliaria profunda | Deepest layer of the skin (dermis); less common | Firm, inflamed bumps that look like goose bumps and may break open | Painful or itchy |
The mildest form, miliaria crystallina, occurs when the opening of the sweat duct on the surface of the skin (sweat pore) is blocked. Miliaria rubra occurs deeper in the skin. Occasionally, the inflamed bumps of miliaria rubra fill with pus, forming miliaria pustulosa. Miliaria profunda is the least common form and affects the dermis.
Risk Factors
Certain conditions make it easier for sweat ducts to become blocked or inflamed. Factors that increase the risk of heat rash include being a newborn, since newborns have immature sweat ducts; living in a hot, humid climate; being physically active; and being on bedrest for a long time while having a fever.
| Risk factor | Why it raises risk | | --- | --- | | Being a newborn | Newborns have immature sweat ducts that block easily | | Living in a hot, humid climate | More sweating under conditions that slow evaporation | | Being physically active | Increased sweat production | | Prolonged bedrest with a fever | Persistent sweating while heat cannot escape |
Complications
Heat rash usually heals without scarring. One complication to be aware of: people with brown or Black skin are at risk of spots of skin that get lighter or darker in response to inflammatory skin conditions — postinflammatory hypopigmentation or hyperpigmentation. These changes usually go away within weeks or months.
A common complication is infection with bacteria, causing inflamed and itchy pustules. If bumps begin filling with pus or the rash is clearly worsening, it is time to get it checked.
How Heat Rash Is Diagnosed
You do not need tests to diagnose heat rash. Your health care provider is usually able to diagnose it by examining the skin.
There is one condition that looks like heat rash worth knowing about. 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. A provider can tell these conditions apart on examination.
Treatment and Self-Care
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. That is often the only treatment needed.
For comfort while it heals, press a cool cloth on your skin or take a cool shower or bath. It may help to let your skin air-dry.
Product choice matters too. Avoid using oily or greasy 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.
| Self-care step | Detail | | --- | --- | | Cool the skin | Press a cool cloth on the skin, or take a cool shower or bath | | Air-dry | Let the skin air-dry after cooling | | Avoid pore-blockers | Skip oily or greasy moisturizers, cosmetics, and sunscreens that can block pores further | | Choose lanolin | Use a moisturizer with wool fat (anhydrous lanolin) to help prevent clogged sweat ducts |
Prevention
Prevention targets the two sides of the equation: less trapped sweat and fewer blocked pores.
In hot weather, dress in loose, lightweight clothing that wicks moisture away from the skin. Do not wrap newborns in too many layers. Limit physical activity in the heat — stay in the shade or in an air-conditioned building, or use a fan to circulate the air. Keep your sleeping area cool and well ventilated.
Avoid creams and ointments that can block pores. Also avoid drugs that cause sweating, such as clonidine, beta blockers, and opioids. If you take one of these medicines, that may be one more reason to stay extra cool in hot weather.
| Prevention habit | Practical tip | | --- | --- | | Dress for evaporation | Loose, lightweight, moisture-wicking clothing in hot weather | | Protect newborns | Do not wrap newborns in too many layers | | Limit heat exposure | Limit physical activity in hot weather; stay in shade or air conditioning, or use a fan | | Cool sleep space | Keep your sleeping area cool and well ventilated | | Avoid pore-blockers | Skip creams and ointments that can block pores | | Watch drug-triggered sweating | Clonidine, beta blockers, and opioids can cause sweating — plan cooling accordingly |
When to See a Doctor
A visit with a health care provider usually is not necessary for heat rash. It usually heals by cooling the skin and avoiding exposure to the heat that caused it.
See your health care provider if you or your child has symptoms that last longer than a few days or the rash seems to be getting worse. If the rash is more severe, you may want to see your primary care provider or a dermatologist (a doctor who specializes in skin disorders) to be sure it is heat rash and not another skin disorder.
Preparing for Your Appointment
Before you go, list the questions you have about your condition. Questions worth asking your health care provider for heat rash include what could have caused the rash, how you can treat it, whether you need to limit physical activity until the rash clears, and how you can prevent it in the future.
| 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
Heat rash is a common, usually harmless condition that forms when a blocked or inflamed sweat duct traps sweat beneath the skin. It comes in four types based on depth — from painless clear bumps (miliaria crystallina) to itchy prickly heat (miliaria rubra), pus-filled variants (miliaria pustulosa), and the rare deep dermal form (miliaria profunda). The treatment for mild cases is beautifully simple: cool the skin, avoid the heat that caused it, and keep pores clear with lanolin-based moisturizers instead of greasy products. The rash usually clears quickly once the skin cools.
If your rash is not improving after a few days, or if it is getting worse, do not guess at it — have a health care provider confirm it is heat rash and not another skin condition.
Frequently Asked Questions
What is heat rash and why does it happen?
Heat rash (prickly heat, miliaria) develops when a duct that leads from a sweat gland to the surface of the skin is blocked or inflamed, blocking the sweat pore. Instead of evaporating, sweat is trapped beneath the skin, causing irritation and bumps. It is common in hot, humid conditions and affects both babies and adults.
What are the four types of heat rash?
The types are classified by how deep the sweat is trapped. Miliaria crystallina (mildest) causes tiny clear fluid-filled bumps that break easily and don't itch. Miliaria rubra (prickly heat) causes small inflamed blister-like bumps with itching or prickling. Miliaria pustulosa is miliaria rubra with pus-filled bumps. Miliaria profunda (less common) affects the dermis and causes firm, painful or itchy bumps that look like goose bumps and may break open.
Does heat rash itch?
It depends on the type. Miliaria crystallina does not hurt or itch. Miliaria rubra, the most common itchy form, causes itching or prickling. Miliaria profunda can be painful or itchy.
How long does heat rash last?
Heat rash usually goes away once the skin cools down, and mild heat rash tends to clear quickly once the skin is cool. If symptoms last longer than a few days or the rash seems to be getting worse, see a health care provider.
How do you treat heat rash fast?
Treatment for mild heat rash is cooling the skin and avoiding exposure to the heat that caused it — press a cool cloth on the skin or take a cool shower or bath, and let the skin air-dry. Avoid oily or greasy moisturizers, cosmetics, and sunscreens that block pores, and use a moisturizer with wool fat (anhydrous lanolin), which helps keep sweat ducts unclogged.
Is heat rash contagious?
Heat rash is not an infection and cannot spread to other people. However, a common complication is bacterial infection of the rash, which causes inflamed and itchy pustules and should be evaluated by a provider.
Can adults get heat rash, or is it only for babies?
Heat rash affects adults as well as babies. Newborns are at higher risk because their sweat ducts are immature, but adults commonly develop heat rash in skin folds and where clothing rubs against the skin, especially in hot, humid conditions.
When should I see a doctor about heat rash?
A visit usually is not necessary. See your health care provider if you or your child has symptoms that last longer than a few days or the rash seems to be getting worse. For more severe rashes, a primary care provider or dermatologist can confirm it is heat rash and not another skin disorder.
Further Reading
Medical disclaimer: This article is for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified health care provider with any questions you may have regarding a skin condition or other health concern. Never disregard professional medical advice or delay seeking it because of content you have read on this site.
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