Heat Rash
An itchy rash from sweat trapped under the skin
Quick Facts
- Type: Common skin condition
- Cause: Blocked sweat ducts in hot, humid conditions
- Common areas: Skin folds, neck, chest, back, areas under clothing
- Treatment: Cooling the skin and keeping it dry
Overview
Heat rash, often called prickly heat, is a common, harmless skin condition that develops when sweat becomes trapped beneath the surface of the skin. This happens most often in hot, humid weather or when the skin is covered, leading to clusters of tiny bumps or blisters, redness, and a prickly or itchy feeling.
The rash occurs when the small ducts that carry sweat to the skin's surface become blocked, so sweat builds up under the skin instead of evaporating. Heat rash is especially common in babies, whose sweat glands are still developing, but it can affect anyone. It is usually mild and clears on its own once the skin cools and dries, though it can be uncomfortable while it lasts.
Symptoms
Heat rash appears in areas where sweat collects, such as skin folds and places covered by clothing. Symptoms include:
- Clusters of small red bumps or tiny clear blisters
- An itchy, prickly, or stinging sensation
- Redness in affected areas
- Mild swelling in some cases
- Most often on the neck, chest, back, groin, elbow creases, and under the breasts
There are different forms ranging from very superficial clear blisters with little discomfort to deeper, red, itchy bumps. While heat rash itself is not serious, signs of infection such as increasing pain, warmth, swelling, pus, or fever, or signs of overheating such as dizziness and a high body temperature, need medical attention.
Causes
Heat rash is caused by blocked sweat ducts that trap sweat under the skin. Common contributing factors include:
- Hot, humid weather: Increases sweating and makes blocked ducts more likely.
- Heavy clothing or coverings: Clothing or bedding that traps heat and moisture against the skin.
- Physical activity: Exercise or hard work that causes heavy sweating.
- Immature sweat glands: In babies, whose sweat ducts develop more easily blocked.
- Prolonged bed rest: Especially with fever or in warm conditions.
Anything that increases sweating or prevents sweat from evaporating can contribute to heat rash.
Risk Factors
- Living in or visiting hot, humid climates
- Being an infant or young child
- Wearing tight or heavy clothing that traps heat
- Intense physical activity that causes heavy sweating
- Being overweight, with more skin folds where sweat collects
- Prolonged bed rest, especially with fever
Diagnosis
Heat rash is usually diagnosed by its appearance and the situation, without special tests:
- Visual examination: A clinician can typically recognize heat rash by looking at the skin.
- History: Recent heat, sweating, or being covered up supports the diagnosis.
- Further evaluation: Rarely needed, but a clinician may consider other causes if the rash is unusual, widespread, painful, or does not improve.
Treatment
Heat rash usually clears on its own once the skin cools and dries. Helpful measures include:
- Cool the skin: Move to a cooler, less humid environment or use a fan or air conditioning.
- Keep the skin dry: Gently dry affected areas and avoid heavy creams that can block sweat ducts further.
- Wear loose clothing: Choose lightweight, breathable fabrics.
- Soothe irritation: Cool baths or showers and gentle, non-greasy lotions can ease itching; a clinician may suggest specific soothing products.
- Avoid scratching: To reduce irritation and lower the risk of infection.
Most heat rash improves within a few days. See a clinician if it does not clear, becomes very itchy or painful, or shows signs of infection.
Prevention
- Stay in cool, well-ventilated environments during hot weather
- Wear lightweight, loose, breathable clothing
- Avoid overdressing babies and check for sweating in skin folds
- Keep the skin clean and dry, especially in skin folds
- Take breaks from heavy activity in the heat
- Avoid heavy ointments and creams that can block sweat ducts
When to See a Doctor
Heat rash is usually mild and clears on its own. See a clinician if:
- The rash does not improve within a few days of cooling and drying the skin
- It becomes increasingly painful, swollen, warm, or develops pus
- There is a fever along with the rash
- The rash is widespread or very uncomfortable
Seek prompt care if there are signs of overheating, such as a high body temperature, dizziness, weakness, or confusion, as these can indicate a more serious heat-related illness rather than a simple rash.
Frequently Asked Questions
What causes heat rash?
Heat rash develops when sweat ducts become blocked and trap sweat under the skin, most often in hot, humid conditions or when the skin is covered. It is especially common in babies, whose sweat glands are still developing.
How do I get rid of heat rash?
Cool and dry the affected skin by moving to a cooler place, wearing loose, breathable clothing, and avoiding heavy creams that block sweat ducts. Most heat rash clears within a few days once the skin can cool and the sweat can evaporate.
Is heat rash dangerous?
Heat rash itself is usually harmless and clears on its own. However, see a clinician if it becomes painful, swollen, or develops pus, which may mean infection, or if there are signs of overheating like a high temperature or dizziness.
Why do babies get heat rash so easily?
Babies have immature sweat ducts that block more easily, and they are often dressed in extra layers. Keeping babies cool, avoiding overdressing, and checking skin folds for sweat helps prevent heat rash.
How can I prevent heat rash?
Stay in cool, ventilated spaces in hot weather, wear lightweight loose clothing, keep skin clean and dry, avoid overdressing, and take breaks from heavy activity in the heat. Avoiding thick ointments that clog sweat ducts also helps.
References
- American Academy of Dermatology. Heat rash.
- MedlinePlus, U.S. National Library of Medicine. Heat rash.
- Mayo Clinic. Heat rash — Symptoms and causes.
- Centers for Disease Control and Prevention (CDC). Heat-related illnesses.