What causes a sweat rash (heat rash/miliaria) and how should it be managed?

Sweat Rash (Heat Rash/Miliaria): Causes and Management

Sweat rash (miliaria) is caused by blockage of eccrine sweat ducts, leading to sweat retention in the skin, and is best managed by cooling the affected areas, keeping skin dry and well-ventilated, and avoiding further heat exposure. 1, 2

Pathophysiology and Causative Factors

Miliaria develops when eccrine sweat ducts become obstructed, preventing normal sweat excretion and causing sweat to accumulate within different layers of the skin 1, 2. The primary triggers include:

• Heat and humidity exposure – Hot, humid climates or thermal stress create the conditions for duct obstruction 1, 3
• Occlusive clothing – Tight-fitting or non-breathable fabrics (particularly synthetic blends and flame-resistant materials) trap sweat against the skin and promote duct blockage 1, 4
• Prolonged sweating – Extended periods of perspiration without adequate skin drying increase risk 4
• Fever – Elevated body temperature from illness can trigger miliaria in hospitalized patients 2

Clinical Presentation by Type

The appearance varies by the depth of duct obstruction:

• Miliaria crystallina – Superficial, fragile, clear fluid-filled vesicles (1-3 mm) resembling water droplets on the skin surface; most common in infants but can occur in febrile adults 1, 2
• Miliaria rubra – Small erythematous papules or vesicles with surrounding inflammation; may progress to secondary bacterial infection (particularly Staphylococcus aureus) if severe 3, 4
• Bullous miliaria – Rare variant with larger bullae formation 1

Immediate Management Strategy

Step 1: Remove heat exposure and cool the skin

• Move the patient to a cool, well-ventilated environment immediately 2
• Apply cool compresses or allow cool water bathing to lower skin temperature 2
• Ensure affected areas remain dry and exposed to air 2, 4

Step 2: Modify clothing and hygiene practices

• Remove occlusive or synthetic clothing; switch to loose-fitting cotton garments 4
• Change clothing regularly when sweating occurs 4
• Ensure thorough laundering to remove detergent residue from fabrics, as residue can worsen irritation 4

Step 3: Topical care for symptomatic relief

• Keep skin clean and dry through good personal hygiene 4
• Avoid heavy emollients or occlusive products that could worsen duct obstruction
• For mild cases, no specific topical treatment is required beyond cooling measures 2

Managing Complications

Secondary bacterial infection (miliaria rubra with superinfection):

• Watch for increased crusting, pustules, or spreading erythema suggesting Staphylococcus aureus superinfection 4
• Prescribe oral flucloxacillin as first-line antibiotic if bacterial infection is confirmed 4
• Erythromycin is an alternative for penicillin allergy 4
• Report to healthcare provider immediately when skin irritation or rash appears, as infected miliaria can become serious 4

Expected Course and Recovery

• Miliaria is self-limiting and resolves spontaneously once heat exposure is removed and skin is kept cool and dry 1, 2
• Miliaria rubra typically takes one week or longer to clear completely, so temporary removal from hot environments or occlusive clothing may be necessary 4
• Full recovery occurs with appropriate environmental modifications and topical care 4

Prevention Strategies

• Avoid prolonged exposure to hot, humid environments when possible 3
• Wear breathable, loose-fitting cotton clothing in hot climates 4
• Change sweat-soaked clothing promptly 4
• Maintain good skin hygiene to keep skin as dry and clean as possible 4
• Individuals with sensitive skin or history of miliaria should take extra precautions in high-temperature settings 4

Common Pitfalls to Avoid

• Do not apply heavy moisturizers or occlusive ointments, as these worsen duct obstruction
• Do not delay reporting skin irritation in occupational settings with heat exposure, as early intervention prevents progression to infected miliaria 4
• Do not confuse miliaria with other vesicular eruptions such as viral exanthems or contact dermatitis; the history of heat/occlusion exposure is key 1, 2