Heat Rash – Symptoms and Causes

ByJanis Updated

Overview

Heat rash, also called prickly heat or miliaria, affects both children and adults. It happens when sweat gets trapped under the skin, usually in hot, humid weather.

The condition shows up in different ways on the skin. Some types form small blisters while others create deeper, inflamed bumps. Many people experience itching with heat rash, which can be quite intense.

Two common types of heat rash include:

  • Miliaria rubra: Small, red, inflamed bumps that often itch significantly.
  • Miliaria crystallina: Clear, fluid-filled bumps that don’t cause pain or itching.

Most cases of heat rash clear up on their own once the skin cools down. However, severe cases might require help from a doctor.

Several products can help manage heat rash symptoms:

  • Cooling powders
  • Calamine lotion
  • Gentle, fragrance-free moisturizers
  • Cool compresses

The best approach is to keep the affected area cool and dry. Wear loose, breathable clothing and avoid activities that cause excessive sweating until the rash heals.

Signs and Symptoms

Heat rash typically appears in areas where skin touches skin or clothing rubs against the body. For adults, it often shows up in skin folds.

Babies usually get it on their neck, shoulders, and chest. The rash can also develop in armpits, elbow bends, and the groin area.

How Sweat Affects the Skin

Your body has two main types of sweat glands. Eccrine glands cover most of your body and release sweat directly onto your skin’s surface. Apocrine glands connect to hair follicles and are mainly found on the scalp, armpits, and groin.

When these sweat glands get blocked, heat rash can develop. Excessive sweating conditions mainly involve eccrine glands, though apocrine glands may also play a role.

Different Forms of Heat Rash

Heat rash comes in several forms, based on how deep the sweat is trapped in the skin:

Miliaria Crystallina (Mild)

  • Tiny, clear, fluid-filled bumps
  • Breaks easily
  • Occurs when sweat pores on the skin surface become blocked

Miliaria Rubra (Moderate)

  • Small, red, inflamed bumps
  • Causes itching or prickling sensations
  • Often called “prickly heat”
  • More uncomfortable than miliaria crystallina

Miliaria Pustulosa

  • Inflamed bumps filled with pus
  • Develops from miliaria rubra

Miliaria Profunda (Severe)

  • Firm, painful, or itchy bumps
  • Resembles goose bumps
  • May break open
  • Affects the deepest skin layer (dermis)
  • Less common than other types

When to See a Doctor

Heat rash typically gets better when you cool the skin and stay away from heat sources. However, you should contact your doctor if:

  • Symptoms last more than a few days
  • The rash appears to be worsening
  • Signs of infection develop (increasing redness, warmth, or pus)

Early treatment can prevent complications and provide relief from uncomfortable symptoms.

Causes

Heat rash happens when sweat can’t escape from the skin. This occurs when:

  • Sweat ducts become blocked or inflamed
  • Sweat pores get clogged on the skin’s surface
  • Perspiration gets trapped under the skin

When sweat can’t evaporate properly, it remains stuck beneath the skin. This trapped moisture irritates the surrounding tissue, leading to the characteristic bumps and discomfort of heat rash.

Risk Factors

Several factors can make heat rash more likely to develop:

  • Newborns have underdeveloped sweat glands, increasing their risk
  • Hot, humid environments create ideal conditions for sweat blockage
  • Physical activity that causes increased sweating
  • Extended periods of bed rest, especially when accompanied by fever

Complications

Heat rash usually resolves fully without causing any scarring. People with darker skin tones may experience temporary changes in skin color where the rash occurred.

These patches may be lighter or darker than the surrounding skin but usually return to normal in a few weeks or months.

Bacterial infection is a possible complication when heat rash develops. This can lead to:

  • Inflamed skin areas
  • Increased itchiness
  • Formation of pus-filled bumps (pustules)

Preventing Heat Rash

To avoid heat rash, wear loose-fitting, light clothing that pulls sweat away from your skin. For babies, avoid using too many blankets or clothing layers.

  • When temperatures rise, try to:
    • Stay in air-conditioned spaces or shaded areas
    • Use fans to improve air circulation
    • Reduce physical activity
    • Keep sleeping areas cool with good airflow
  • Avoid these items that can worsen heat rash:
    • Thick creams and ointments that block skin pores
    • Medications known to increase sweating (including certain blood pressure medications and pain relievers)

Making these simple changes can significantly reduce your risk of developing uncomfortable heat rash during hot weather.


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Health Writer

Janis's areas of expertise include nutrition, exercise, stress management, and mental health. She is passionate about educating and empowering people to take control of their health and make positive changes that can last a lifetime. Janis believes that small, sustainable changes are the key to long-term success, and she works with her clients to develop personalized plans that fit their individual needs and lifestyles.