Heat rash, also known as prickly heat, sweat rash, and miliaria, is a pimple-like rash caused by the blockage of sweat glands. The bumps or blisters associated with heat rash are sometimes referred to as sweat bumps or bubbles. Depending on the type of heat rash, it may be itchy or painful. In most cases, cooling the skin clears the rash.
Table of Contents
What is heat rash?
Heat rash is a skin condition that occurs when eccrine sweat glands or ducts become blocked, preventing sweat from escaping onto the surface of the skin. This leads to tiny bumps on the skin, which may resemble pimples.
The condition occurs commonly in hot and humid conditions. It is frequently seen in areas covered by heavy clothing or between skin folds where air cannot flow freely. It can affect individuals of all age groups.
Medical term for it
The medical term for heat rash is “miliaria.” The condition is categorized into various forms based on the depth of the sweat gland blockage: miliaria crystallina, miliaria rubra, and miliaria profunda. Each form has distinct characteristics and symptoms that can range from mild to severe.
Other names
Heat rash is also commonly known by other names such as:
- Prickly heat
- Sweat rash
- Summer rash.
Causes
The primary cause of heat rash is blocked sweat glands and ducts. This can occur for various reasons, including:
- Hot, humid weather
- Intense physical exercise
- Tight and/or synthetic clothing
- Fever
- Overheating due to blankets or heaters
- Occlusive skincare products
- Certain medications that induce sweating
- Babies are especially prone to heat rash, as their sweat glands are still developing.
Pictures
Below are pictures that show heat rash on different areas of the body.
Appearance
A heat rash looks like a cluster of small blisters or raised red bumps on the skin (depending on the type of heat rash). These sweat bumps may sometimes resemble pimples. The skin surrounding these bumps can be red and irritated forming red patches.
In people with darker skin tones, including brown, dark brown, or black skin, the bumps of heat rash may appear as white, gray, purple, or dark brown. Sometimes, it may be challenging to spot heat rash in darker skin tones.
Associated symptoms
Symptoms can vary depending on the severity of the condition and may include:
- Redness or a pinkish color around the affected area
- An itchy or prickly feeling
- Mild inflammation or swelling
- Tenderness to the touch
- Persistent itching, which may lead to sores
Location
Heat rash can appear anywhere on the body but more commonly tends to appear in areas where there’s friction or where sweat is likely to accumulate.
Common areas affected by heat rash include:
- Armpits
- Inner thighs
- Waistline
- Chest
- Back
- Belly or stomach area
- Under the breasts
- Groin
- Around the neck
- Arms and legs, especially behind the knees and on the inner side of the elbow
It often shows up in areas of the body covered by clothing, such as the waistband of pants or a dress. Another example would be heat rashes on the forehead due to a headband.
Occlusive patches and certain skincare products can also trigger heat rash. Similarly, thick and occlusive hair care products may cause heat rash on the forehead, hairline, or scalp. Masks and scarves can also lead to heat rash on the face.
Types
There are three distinct types of heat rash, each with a different appearance and symptoms.
1. Miliaria crystallina (Mild heat rash)
Also known as sudamina, miliaria crystallina is the mildest form of heat rash. It is characterized by small, clear, or white fluid-filled bumps on the skin’s surface.
These bumps are very superficial and are located in the stratum corneum of the skin (the topmost layer). They may resemble water droplets or dewdrops and can rupture easily.
This type can occur in both babies (especially those who are 2 weeks old or younger) and adults. It causes little or no inflammation and rarely leads to itching or discomfort.
2. Miliaria rubra
Miliaria rubra is the most common type of heat rash and is often referred to as prickly heat. This form occurs due to the obstruction of sweat ducts deeper within the skin, specifically in the middle of the epidermis, and is associated with inflammation.
Symptoms commonly include red spots or bumps, itching, and a prickly sensation. When pus-filled bumps or pustules are present, this condition is specifically called miliaria pustulosa.
In babies, miliaria rubra typically affects skin folds such as the groin, axilla, and neck. In adults, it is frequently seen on the chest, back, arms, legs, scalp, and neck, as well as in skin flexures, particularly in areas where clothing creates friction against the skin.
3. Miliaria profunda
Miliaria profunda is the least common type of heat rash and affects the deeper dermal layer of the skin. It often occurs in adults who have had repeated episodes of miliaria rubra or who have been exposed to a new hot climate.
The bumps are larger, flesh-colored, and can be painful. They may or may not cause itching. The trunk, specifically the chest and back, is usually the area most affected.
Read more: Is heat rash itchy?
How long does a heat rash last?
Mild heat rash usually lasts for 2-3 days. More severe forms can last for weeks if not properly treated. If your heat rash persists beyond 2-3 days, it’s best to consult a doctor for proper management.
Can heat rashes spread?
Heat rash can spread on the body if exposure to triggering factors such as hot weather persists, leading to continuous blockage of the sweat ducts.
Is it contagious or can it spread to others?
Heat rash is not contagious because it results from blocked sweat glands. It is not caused by bacteria, viruses, or fungi that could be transmitted to other people.
Diagnosis
The diagnosis is generally made through a visual examination of the skin lesions and by taking the patient’s history.
Factors such as recent exposure to hot and humid conditions often assist in making the diagnosis. Additional tests are seldom necessary unless there’s a possibility of infection or another underlying condition.
Look-alikes
Heat rash is often mistaken for other skin conditions or rashes, which are discussed below, due to its characteristic small red bumps.
- Keratosis pilaris: This condition presents with small, rough bumps which are usually seen on the upper arms, thighs, and sometimes the face. It is known for its “chicken skin” appearance. Keratosis pilaris typically doesn’t itch.
- Folliculitis: This condition is characterized by red, inflamed bumps that often contain pus and surround a hair follicle. They may be itchy or painful and can develop after activities like shaving or waxing, or from wearing tight clothing. Folliculitis can have various causes, including bacteria and fungi.
- Pimples (acne vulgaris): These appear as red or inflamed bumps, blackheads, whiteheads, or cysts and usually don’t itch. They are most commonly found on the face but can also appear on the back, shoulders, and chest. The bumps occur when pores become clogged with oil, dirt, and dead skin cells.
- Chickenpox: This disease presents as a red, itchy rash that turns into fluid-filled blisters. Initially, the rash appears on the face and trunk but can spread to other parts of the body. Chickenpox is often accompanied by other symptoms like fever, fatigue, and headaches. It is caused by the Varicella-Zoster virus and is contagious.
- Rashes in newborns: Conditions such as erythema toxicum neonatorum, transient neonatal pustular melanosis, and neonatal acne can be mistaken for heat rash.
Treatment
The treatment of heat rash will depend on the severity. In most cases, a heat rash resolves on its own. Home remedies or treatments may help in clearing them faster.
1. Home remedies
- Environment: To alleviate heat rash, consider staying in areas with an air conditioner or a fan to circulate the air. This can help reduce the likelihood of sweat accumulation, which can worsen the condition. Additionally, avoid strenuous exercise in hot and humid environments.
- Soothing oatmeal baths: An oatmeal bath can help relieve the irritation and itching associated with heat rash. Oatmeal has anti-inflammatory and moisturizing properties that can provide immediate relief.
- Apply a cold compress or take a cool bath: Cold compresses or a cool bath can reduce inflammation and provide instant relief from the burning sensation often associated with heat rash. For a cold compress, wet a clean cloth with cold water, or wrap a few ice cubes in a thin towel. Apply the compress to the affected area for 5-10 minutes.
- Wear appropriate clothing: The fabric of your clothing can either exacerbate or alleviate symptoms. Choose loose-fitting clothes made of breathable, natural fibers like cotton or linen. These fabrics allow the skin to breathe more easily, helping sweat to evaporate.
- Use lightweight skincare products: Use lightweight skincare products and avoid those that are heavy or occlusive.
- Avoid irritating substances: Stay away from products containing fragrances, essential oils, or other potential irritants that can worsen your condition.
2. Over-the-counter options for itch relief
For persistent itching, you can use over-the-counter options like calamine lotion or aloe vera gel. These products offer a cooling sensation and can soothe the skin.
Over-the-counter steroid creams like hydrocortisone can reduce inflammation and itching but should be used cautiously and for short periods unless advised otherwise by a healthcare provider.
Antihistamines can also help in relieving itching.
3. Prescription treatments
If your symptoms are severe or not improving with over-the-counter treatments, it may be necessary to consult a healthcare provider for a more detailed treatment plan.
Topical steroids could be prescribed to reduce inflammation. In severe cases, oral steroids such as prednisone may be considered.
These treatments have their own risks and side effects, so it’s important to always follow your doctor’s recommendations.
Complications
Though often considered a minor issue, untreated or severe heat rash can result in complications such as secondary bacterial infections, chronic itch, or scarring.
When a large area of the body is affected, there is also a risk of developing heat exhaustion. Therefore, it is important to consult a doctor for persistent or severe symptoms.
When to see a doctor
One should see a doctor if:
- The heat rash doesn’t go away within 3 days or worsens over time.
- The rash is causing significant pain or uncontrollable, intense itching.
- The rash is accompanied by systemic symptoms like fever, nausea, or vomiting.
- There’s pus or a foul-smelling discharge.
Prevention
To prevent heat rash, consider the following measures:
- Avoid hot environments and opt for cooler areas with air conditioning or fans.
- Avoid strenuous exercise in hot conditions. Instead, choose cooler times or environments for physical activity.
- Wear loose-fitting clothes made of breathable materials.
- Consider taking a cool bath if exposed to extreme heat.
- For babies, allow some diaper-free time to let the diaper area air-dry.
- Stay hydrated by drinking plenty of water.
- Avoid using thick ointments or occlusive creams.
Key points
Heat rash is also known as sweat rash, prickly heat, and summer rash. It is caused by blocked sweat glands and ducts.
There are different types of heat rash, with miliaria rubra being the most common. Symptoms may include sweat blisters or bumps surrounded by red skin and a prickly sensation.
Cooling the skin often clears the heat rash in 2-3 days, but if your rash worsens or doesn’t improve, it’s best to consult a healthcare provider for proper diagnosis and treatment.
References
- Guerra KC, Toncar A, Krishnamurthy K. Miliaria. [Updated 2023 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan.
- LUBOWE II, PERLMAN HH. Periporitis staphylogenes and other complications of miliaria in infants and children. AMA Arch Derm Syphilol. 1954 May;69(5):543-53. doi: 10.1001/archderm.1954.01540170013002. PMID: 13147561.
Disclaimer: This article is for information purposes only and does not replace medical advice.