Complete Guide to Heat Rash Types: Causes and Solutions

With the arrival of higher temperatures, many people experience skin discomfort, including itching and irritation in different areas of the body. The types of rashes that appear during intense heat and excessive humidity are common conditions that especially occur on the neck, shoulders, chest, and skin folds. But understanding what heat rash types are and how to address them is essential for proper care.

Understanding miliaria: why it occurs

Although popularly known as “heat rash,” this term is not the official diagnosis used by specialists. Miliaria, as it is technically called, occurs when sweat glands and their ducts become blocked due to high heat and humidity. According to Dr. Angela Lamb, a board-certified dermatologist at Mount Sinai in New York, “when sweat gets trapped under the skin, small bumps or vesicles appear that usually itch or cause discomfort.”

This heat irritation, also known as prickly heat or sweat rash, almost always causes a sensation of itching. Experts recognize that the severity varies depending on where the blockage is located within the skin layers.

Three categories of heat irritation you should know

Heat rash types are classified into three distinct categories based on the depth of the blockage:

Miliaria crystallina - The mildest form mainly occurs in newborns when the obstruction happens at the superficial level of the sweat duct opening. It appears as tiny sweat droplets trapped under raised skin, without inflammation or significant itching, and generally has a very clear coloration, sometimes without visible redness.

Miliaria rubra - The most common type, affecting newborns and up to 30 percent of adults in warm, humid regions. Dr. Rajani Katta, a board-certified dermatologist in Houston, describes it as “characterized by its intense red color, pronounced itching, and appearance of small bumps.” This variant occurs when sweat is blocked in the middle layer of the epidermis, a deeper layer than the previous one.

Miliaria profunda - The least common presentation occurs when the obstruction affects the dermis, the deepest layer of the skin. Although it causes less itching compared to rubra, the bumps tend to be firmer, more red, and cause more noticeable pain.

These three categories usually develop in areas where the skin overlaps, such as armpits, groin, neck, abdomen, and under the breasts. In babies, it frequently appears on the neck, shoulders, and torso. Tight clothing increases the likelihood of developing this condition. Newborns are more vulnerable due to their underdeveloped sweat ducts and greater number of skin folds, especially if kept very warm in hot environments.

Key differences from other skin conditions

Distinguishing heat rash from other dermatological issues is essential. Dr. Lamb notes that it is often confused with eczema, “which can worsen during extreme and humid summer climates.” Eczema is an inflammatory condition that causes itching, dryness, rashes, blisters, and potential infections.

With mild eczema, symptoms may not be experienced in temperate weather, but flare-ups can occur during heat that resemble heat irritation. Dr. Katta adds that “both can appear red and itchy, and sometimes occur in similar areas.” The main difference is that eczema tends to look more irregular and flaky, with imprecise borders and flat areas, while heat rash forms clearly defined bumps.

Another condition often confused is polymorphic light eruption, characterized by inflamed bumps or slightly raised patches that cause itching or burning. According to Dr. Lamb, people often notice it “during prolonged sunny vacations after months of low sun exposure.” Although it can occur at any time, it typically appears in spring or early summer when traveling to areas with higher solar radiation. The distinctive feature of this rash is that “unlike heat rash, it is not caused by temperature or humidity, but specifically by solar radiation.”

Treatment and prevention strategies

Anyone can develop heat irritation. If it appears, the first recommended step by Dr. Lamb is “to move to a cooler environment, seek shade, and avoid the hottest and most humid hours.” Dr. Nadine Kaskas, also from Mount Sinai, suggests “removing tight clothing and washing thick lotions like sunscreens that hinder skin breathing.”

Cold compresses with a clean towel or a cold shower provide immediate relief. Over-the-counter ointments like calamine lotion can help reduce itching, but if discomfort persists, consulting a doctor for prescription topical steroids is necessary.

Without treatment, this condition usually resolves on its own after leaving hot and humid environments, although there is a risk of infection if vesicles open without proper hygiene.

Effective preventive measures: To avoid overheating, Dr. Kaskas recommends seeking shade, taking breaks from activities, avoiding excessive exertion, and maintaining constant hydration. Dr. Lamb advocates for portable fans that can be hung around the neck. Dr. Katta emphasizes the importance of wearing breathable, loose, and lightweight clothing that “allows sweat to evaporate from the skin.”

Finally, Dr. Katta warns that “this irritation serves as a warning sign that sweat glands are not functioning optimally, which could increase vulnerability to heat exhaustion or heatstroke.” In case of any irritation during high temperatures, it is wise to take immediate measures to cool down.