Causes of Heat Rash
Heat rash (miliaria) is primarily caused by blocked sweat ducts and trapped sweat under the skin, occurring when excessive sweat accumulates on the skin surface for prolonged periods, especially in hot and humid environments. 1
Primary Causes and Risk Factors
Environmental Factors:
- Hot and humid weather conditions 2
- Prolonged exposure to heat sources 3
- Thermal stress in tropical climates, particularly during summer months 4, 5
- Inadequate cooling or ventilation in living environments
Physical Factors:
- Occlusion of sweat ducts leading to sweat retention 4
- Excessive sweating (hyperhidrosis) 1
- Prolonged skin-to-skin contact in skin folds
- Areas with limited air circulation (axillae, groin, under breasts)
Clothing and Equipment:
- Tight-fitting clothing that prevents sweat evaporation 2
- Non-breathable synthetic fabrics
- Protective equipment or uniforms that contribute to excessive heat retention 2
- Occlusive dressings or bandages
Activity-Related Factors:
- Vigorous physical activity in hot environments 2
- Insufficient rest periods during exercise in heat 2
- Poor acclimatization to hot weather 2
- Inadequate hydration during physical exertion 2
Individual Risk Factors:
- Obesity or overweight status (BMI ≥ 85th percentile for age) 2
- Poor physical fitness 2
- Inadequate pre-hydration before heat exposure 2
- Current or recent illness, especially with fever or gastrointestinal symptoms 2
- Certain medications that affect sweating or temperature regulation 2
- Atopic dermatitis, which can lead to attenuated sweating ability 1
- Decreased tight junction integrity in sweat glands (particularly in atopic dermatitis patients) 1
Clinical Manifestations
Heat rash presents in several forms:
- Miliaria crystallina: Superficial clear vesicles without inflammation
- Miliaria rubra: Erythematous papules and vesicles with pruritus (prickly heat)
- Miliaria pustulosa: Pustular lesions that may show a "hypopyon sign" 5
- Miliaria profunda: Flesh-colored papules with minimal inflammation
In severe cases, particularly in tropical regions, "sweat dermatitis" may develop with:
- Dry, hyperpigmented, fissured "parchment-like" skin 5
- Shiny "crinkled cellophane paper-like" skin 5
- Asymptomatic hyperpigmented macules 5
- Linear and parallel ridge patterns of dermatitis 5
Prevention Strategies
To prevent heat rash:
- Wear loose-fitting, lightweight, light-colored clothing in hot weather 3
- Ensure adequate ventilation and use air conditioning when possible 3
- Take regular breaks from heat exposure 2
- Maintain proper hydration before, during, and after heat exposure 2, 3
- Gradually acclimatize to hot environments 2
- Shower promptly after sweating to remove salt and sweat residue
- Use absorbent powders in skin fold areas prone to moisture accumulation
- Monitor for early signs of heat-related illness during physical activity 2
Special Considerations
- Individuals with atopic dermatitis are particularly susceptible to heat rash due to impaired sweating function and compromised skin barrier 1
- People with mastocytosis or other mast cell disorders may experience more severe heat-triggered reactions 3
- Those with small fiber neuropathy may have compounded temperature regulation issues 3
- Children and adolescents participating in sports require special attention to prevent heat-related illnesses, including heat rash 2, 6
Understanding the causes of heat rash is essential for effective prevention and management, especially as global temperatures rise and heat-related illnesses become more prevalent.