Miliaria Crystallina

The mildest and most superficial form of miliaria. The sweat duct is blocked within or just beneath the stratum corneum, so sweat collects in thin walled, clear vesicles without inflammation.

• It is most common in neonates (in the first 2 weeks of life, when sweat ducts are immature) and in adults after fever, heavy sweating, sunburn, or prolonged bed rest in a hot environment. Sunburn damages the duct and stratum corneum, so the eruption appears on sunburnt skin after 1 to 2 weeks.
• Occlusion by dressings, incubators, overwrapping, and thick creams is a frequent cause. Drugs that increase sweating (bethanechol, clonidine, doxorubicin) can contribute.
• It is harmless, self-limiting and needs no treatment beyond removing the cause.

• Crops of 1 to 2 mm clear, dewdrop like, thin walled vesicles with no surrounding redness, which rupture with light touch. They look like droplets of water on the skin.
• Typical sites: the head, neck, upper trunk, and in infants the face and chest. There is no itch, pain or burning.
• Lesions dry and desquamate in 24 to 72 hours as fine scale, leaving normal skin.
• Differential diagnosis: miliaria rubra (red, itchy, papular), miliaria profunda, herpes simplex or varicella (grouped, umbilicated vesicles, with fever), impetigo, scabies, sudamina with fever, early bullous disease, and drug eruption.
• Red flags: fever with a vesicular eruption in an ill infant (needs exclusion of sepsis and herpes simplex), and signs of heat illness.
• Complications are rare. Progression to miliaria rubra can occur with continued sweating.

• Clinical. The absence of redness, itch and pain, with clear fragile vesicles in a hot setting, is typical.
• If an infant is unwell or the vesicles are grouped or umbilicated, swab for herpes simplex polymerase chain reaction and bacterial culture, and assess for sepsis.
• Biopsy is not needed. It shows a subcorneal or intracorneal vesicle with no inflammation.

• No drug treatment is required. The aims are cooling and removal of the cause:
  • Reduce temperature and humidity, use fans or air conditioning, and remove excess clothing and bedding.
  • Dress infants in light, loose cotton, and avoid overwrapping and incubator overheating.
  • Cool showers or tepid baths, followed by gentle patting dry.
  • Stop heavy creams, oils and occlusive dressings.
  • Maintain oral fluids.
• Calamine lotion can be applied once or twice daily if the area is bothersome, though this is rarely needed.
• Avoid topical steroids and sensitising antiseptics, as they add nothing and may irritate.
• Treat the underlying fever or sunburn: paracetamol 15 mg/kg orally 6 hourly in children (maximum 60 mg/kg per day), or 1 g 6 hourly in adults, and cool compresses for sunburn.
• Special groups:
  • Neonates: examine for infection when there is fever, poor feeding or lethargy, and do not assume a benign cause.
  • Pregnancy: the same measures apply.
  • Bedridden adults: reposition, air the skin, and use breathable sheets.
• Follow up: the eruption clears in 1 to 3 days after cooling, with fine scaling. Review if it persists beyond 1 week, becomes red or itchy (miliaria rubra), or if systemic symptoms appear.