Miliaria

Aka: Miliaria, Miliaria Rubra, Miliaria Alba, Miliaria Sudamina, Apocrine Miliaria, Miliaria Crystallina, Miliaria Profunda, Heat Rash, Sweat Rash, Lichen Tropicus, Prickly Heat, Fox-Fordyce Disease

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II. Epidemiology

  1. Occurs in all ages, but more common children (and 40% of newborns) whose Sweat Glands are under-developed

III. Pathophysiology

  1. Sweat retention when Eccrine Glands (Sweat Glands) partially close or are obstructed by Stratum Corneum
  2. Provoked by excessive sweating
  3. Similar pathophysiology to Milia, but these two conditions are not the same

IV. Types: Common

  1. Miliaria Crystallina (Miliaria Alba, Miliaria Sudamina): Yellow Lesions
    1. Typically seen in newborns (up to 90%) in first week of life
    2. Sweat infiltrates below Stratum Corneum
    3. Vesicles 1-2 mm without surrounding erythema on head, neck and trunk
      1. Noninflammatory Vesicles resemble water droplets
      2. Each Vesicle ruptures and then desquamates and resolves within days
  2. Miliaria Rubra (Heat Rash or Prickly Heat, default type of Miliaria): Red Lesions
    1. Most common form of Miliaria, occurring in children and adults who travel to warm environments
    2. Sweat infiltrates deeper, below Epidermis
      1. Inflammation associated with Sweat Gland obstruction
    3. Pruritic erythematous Papules and Vesicles on covered (over-heated) skin

V. Types: Other

  1. Apocrine Miliaria (Fox-Fordyce Disease)
  2. Miliaria Profunda
    1. Asymptomatic, flesh colored, small, deep Papules on the trunk and extremities
    2. Complication of severe Miliaria Rubra occurring in hot, humid climates

VI. Risk Factors

  1. Newborns (Miliaria Crystallina)
    1. Immature Sweat Glands
  2. Excessive sweating
    1. Acutely, on travel to hot, humid environments
    2. Intense Exercise
    3. Fever
    4. Occlusive clothing
    5. Hyperhidrosis

VII. Symptoms

  1. Very pruritic rash

VIII. Signs: Newborns with Miliaria Crystallina (Miliaria Alba, Miliaria Sudamina)

  1. Tiny (1-2 mm) superficial fragile Vesicles without inflammation
  2. Distributed over the head, neck and upper trunk

IX. Signs: Children and Adults with Miliaria Rubra

  1. Characteristics
    1. Initial: Intensely pruritic, small (2-4 mm) Vesicles and Papules on erythematous base
    2. Next week: Vesicles fill keratin and obstruct Sweat Glands
    3. Next: Obstructed Sweat Glands rupture and form deeper inflammation, and may persist for weeks
  2. Distribution
    1. Children: Neck, Axilla and groin
      1. Intertriginous areas and occluded areas
    2. Adults: Scalp, neck, upper trunk and extremity flexor surfaces
      1. Areas of friction (where clothes rubs against skin)

X. Differential Diagnosis: Newborns with Miliaria Crystallina (Miliaria Alba, Miliaria Sudamina)

  1. See Neonatal Pustules and Vesicles
  2. Erythema Toxicum Neonatorum
  3. Neonatal HSV
  4. Acne Neonatorum

XI. Differential Diagnosis: Children and Adults with Miliaria Rubra

  1. Viral Exanthem
  2. Varicella Zoster Virus
  3. Herpes Simplex Virus
  4. Superficial Folliculitis
  5. Acne Vulgaris
  6. Stevens-Johnson Syndrome (or Toxic Epidermal Necrolysis)

XII. Management

  1. No treatment is typically needed (esp. in newborns with Miliaria Crystallina)
    1. In newborns, resolves spontaneously in first few months of life
    2. Individual lesions resolve in days
    3. Treat secondary infections (e.g. Impetigo)
  2. Stay in cooler environment with reduced sweating
  3. Change clothing to breathable, loosely fitting, clean, dry, cotton
  4. Avoid lotions (occlusive and may obstruct Sweat Glands)
  5. Avoid skin irritants and use only products free of perfume and dye

XIII. Prevention

  1. Avoid Occlusion and excessive heat
  2. Avoid over-dressing
  3. Consider cool baths (avoid prolonged exposure due to Hypothermia)
  4. Stay in cool air conditioned environments

XIV. Complications

  1. Chronic dermatitis
    1. May follow more severe Heat Rash
  2. Secondary Bacterial Skin Infection
    1. Superinfection, typically from scratching

XV. Resources

  1. DermNet NZ
    1. https://dermnetnz.org/topics/miliaria/

XVI. References

  1. Claudius and Behar in Herbert (2020) EM:Rap 20(8): 5-7
  2. Salinas and Ruttan (2017) Crit Dec Emerg Med 31(9): 3-10
  3. Zink (2020) Crit Dec Emerg Med 34(3): 19-27
  4. Feng (1995) Cutis 55:213-6 [PubMed]
  5. O'Connor (2008) Am Fam Physician 77:47-52 [PubMed]

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