Heat Rash in Children

Heat rash in children is miliaria (sweat rash, prickly heat), caused by blockage of eccrine sweat ducts and leakage of sweat into the epidermis or dermis, common in infants and young children in hot, humid conditions, with overdressing, fever, occlusive dressings, or incubator care.

• Types by the level of obstruction:
  • Miliaria crystallina: superficial blockage in the stratum corneum; clear 1 to 2 mm thin walled vesicles resembling dewdrops; non-inflamed, asymptomatic; resolves in 1 to 3 days with desquamation.
  • Miliaria rubra: deeper blockage in the epidermis; erythematous papules and papulovesicles with itch and prickling, in clothed areas (neck, trunk, skin folds, axillae, groin, forehead); may become pustular (miliaria pustulosa).
  • Miliaria profunda: dermal blockage, rare in children; flesh coloured deep papules, with risk of anhidrosis and heat intolerance.
• Pathogenesis includes Staphylococcus epidermidis biofilm in sweat ducts and wet skin maceration.
• Usually self-limiting within days when the child is cooled.
• Complications: secondary bacterial infection (periporitis staphylogenes, sweat gland abscesses), post-inflammatory changes; heat exhaustion in extreme conditions.

• Clusters of tiny red papules, pinpoint vesicles or pustules in areas with sweat and friction (neck, upper chest, back, armpits, skin folds, scalp, forehead, diaper area); itching or prickling; the child is otherwise well.
• Crystallina: clear, fragile droplets without redness.
• Rash flares with heat, exercise, tight clothing, fever, sweating.
• Red flags: fever with a spreading rash, pus or crusting (impetigo or abscess), signs of heat illness (flushed skin, listlessness, vomiting, rapid pulse, high temperature), non-blanching rash, rash with mucosal involvement, persistent beyond 2 weeks, blistering, rash in a neonate with fever (sepsis), eczema, scabies with burrows.

• Clinical diagnosis from the appearance, distribution and trigger.
• Swab for culture if pustules or crusts suggest infection. Skin scraping for Candida if flexural satellite lesions.
• Differentials: folliculitis, candidiasis, atopic dermatitis, contact dermatitis, scabies, erythema toxicum neonatorum, viral exanthem, impetigo, chickenpox, sudamina.

• Cooling and prevention (the mainstay):
  • Move the child to a cool, ventilated environment; remove excess clothing and bedding; dress in loose, light, breathable cotton; avoid synthetic fibres and tight clothing.
  • Use a lukewarm bath or shower (not cold) with gentle cleansing and patting dry; avoid soaps in excess.
  • Keep skin folds dry; air exposure; avoid heavy creams, ointments, petroleum products and occlusive dressings or sunscreens on affected skin.
  • Keep infants' sleeping environment between 16 and 20 C; maintain hydration; avoid overheating by swaddling or overdressing.
• Symptomatic: calamine lotion or cool compresses for itch; lukewarm oatmeal bath; hydrocortisone 1 percent cream applied thinly once or twice daily for 3 to 5 days for troublesome inflamed itchy rash (not on the face of infants for longer periods).
• Secondary infection: mupirocin 2 percent ointment three times daily for 5 days; oral flucloxacillin 12.5 to 25 mg/kg four times daily for 5 to 7 days for extensive infection or abscess (incision and drainage of abscesses).
• Miliaria profunda or recurrent forms: avoid heat, topical anhydrous lanolin.
• Candida complication: clotrimazole 1 percent cream twice daily for 7 to 14 days.
• Expect resolution within a few days of cooling, with desquamation in crystallina.
• Seek review if the rash persists for over a week despite cooling, or if signs of infection or heat illness develop.