Skin rash caused by heat: symptoms, causes, and treatment

Extreme heat and high humidity create the perfect environment for skin rashes to appear, a common condition during the summer months. This dermatological issue, medically known as miliaria, occurs when the skin cannot properly regulate sweating, resulting in irritation, itching, and inflammation in different areas of the body. As temperatures rise, it is crucial to understand what causes this skin rash, how to identify it, and when to seek medical help.

How does skin rash form during summer?

The mechanism behind skin rash is relatively simple: when heat and humidity are excessive, sweat glands and their ducts become blocked. Sweat gets trapped under the skin, creating small bumps, blisters, or inflamed bumps. Although commonly called “heat rash,” certified dermatologists like Dr. Angela Lamb from Mount Sinai in New York explain that miliaria is the precise medical term for this condition.

This skin rash tends to develop in areas where the skin folds over itself: armpits, groin, neck, abdominal folds, and under the breasts. In babies, it frequently appears on the neck, shoulders, and chest, as their sweat ducts are still developing and their multiple skin folds facilitate obstruction.

Tight clothing worsens the problem by preventing the skin from breathing properly. Newborns are more vulnerable, especially if they are overdressed during hot days, although anyone can develop this condition if exposed to sustained heat and humidity.

Three types of miliaria and their different characteristics

There are three categories of miliaria, each determined by the depth of obstruction in the skin layers:

Miliaria crystallina: The mildest and most common in newborns. It occurs when obstructions form at the superficial openings of sweat ducts. Visually, it appears as small sweat droplets trapped under raised skin, with no significant inflammation, itching, or redness. In some cases, it is barely noticeable.

Miliaria rubra: The most common type in adults, affecting up to 30% of people living in warm, humid climates. It is characterized by intense redness, pronounced itching, and a texture of small inflamed bumps. According to Dr. Rajani Katta, a certified dermatologist in Houston, this type occurs when sweat is blocked in the middle epidermis, a deeper layer of the skin. It is the most bothersome version and requires attention.

Miliaria profunda: The least common form, arising when the obstruction reaches the dermis, the deepest layer of the skin. Although it causes less itching than miliaria rubra, the bumps are firmer, more red, and generally more painful.

Differences between heat rash and other skin conditions

Skin rash is often confused with other dermatological conditions, which can lead to inappropriate treatments. Correctly distinguishing them is essential for proper management.

Skin rash vs. eczema: Eczema is a chronic inflammatory condition that can worsen dramatically with summer heat and humidity. Both conditions can be red, itchy, and appear in similar areas of the body. However, eczema tends to look irregular and scaly, with areas that itch more flat and poorly defined at the edges. In contrast, skin rash presents with more defined and distinct bumps. People with mild eczema may not notice symptoms in mild weather but experience intense flare-ups when it gets hot.

Skin rash vs. polymorphic light eruption: This is a unique condition characterized by small inflamed bumps or slightly raised patches of skin with itching or burning. Unlike heat rash, polymorphic light eruption is not caused by temperature or humidity but by sun exposure. It typically occurs when people take sunny vacations after spending months in winter, exposing their skin to much more solar radiation than usual. Symptoms mainly appear in areas directly exposed to the sun.

Immediate treatment for skin rash

If you develop a skin rash, the first step is to move away from the warm, humid environment. Seek shade, go to an air-conditioned or well-ventilated area, and avoid peak heat hours.

Quick measures that work:

• Remove tight clothing: Switch to loose garments that allow your skin to breathe
• Wash the skin: Remove thick lotions like sunscreen or moisturizers that could clog pores
• Apply cold: Take a cold shower or use cold compresses with a clean cloth to soothe irritation
• Use over-the-counter ointments: Calamine lotion helps calm itching
• Consult a doctor if it persists: If the rash becomes especially uncomfortable or does not improve, a dermatologist can prescribe topical steroid creams

When untreated, skin rash usually resolves on its own once you move away from heat and humidity. However, there is a risk of infection if blisters open and the skin is not kept clean.

Prevention strategies: keep your skin safe

If you need to spend time outdoors during extreme heat, adopt preventive measures to avoid overheating:

• Seek shade regularly: Do not stay under direct sunlight continuously
• Take frequent breaks: Interrupt physical activities
• Avoid excessive exertion: Do not overexert yourself in hot weather
• Stay hydrated: Drink water constantly
• Use portable fans: Many dermatologists recommend small neck fans to maintain airflow
• Choose breathable clothing: Wear lightweight, loose garments that allow sweat to evaporate properly. Fabrics like cotton and quick-drying technical materials are ideal

Dr. Nadine Kaskas from Mount Sinai emphasizes the importance of wearing clothing that keeps your body cool and allows proper sweat evaporation.

An important warning about skin rash

According to Dr. Katta, skin rash serves as a warning sign that your sweat glands or ducts are not functioning optimally. This could indicate that you are more vulnerable to more serious heat-related conditions, such as heat exhaustion or heatstroke. If you notice skin irritation while exposed to heat, take immediate measures to cool down and prevent more serious complications.

Anyone can develop skin rash, but awareness of its causes, symptoms, and treatment allows effective management during the hottest months.