General approach to rashes

This page is for adult patients; for other age groups see pediatric rashes and neonatal rashes


  • A wide range of benign and dangerous pathology can present with a rash

Rash Red Flags[1]

  • Fever
  • Toxic appearance
  • Hypotension
  • Mucosal lesions
  • Severe pain
  • Very old or young age
  • Immunosuppressed
  • New medication

Dermatology Nomenclature

Small lesions (<0.5cm)

  • Macule – flat, cirumscribed, colored, non palpable
  • Papule – raised, solid and palpable
  • Vesicle – raised, palpable, clear fluid-filled
  • Pustule – raised, palpable, pus filled (leukocytes or keratin)

Large lesions (>0.5cm)

  • Patch – large macule (flat non-palpable colored area)
  • Plaque – superficially raised, circumscribed solid area
  • Nodule – distinct large papule
  • Bulla - large vesicle (blisters if epidermal layer completely sloughed off)
  • Wheal – firm and edematous plaque (edema of the dermis)


  • Plaque/scaley papule
  • Eschar
  • Erosion/ulcer
  • Purpura/petechia
  • Plaque/smooth papule

Clinical Features


  • Key elements from the history include:
    • Distribution and progression of the skin lesions
    • Recent exposures (sick contacts, foreign travel, sexual history and vaccination status)
    • Any new medications

Physical Exam

  • Pay specific attention to vital signs
    • A rash associated with fever or hypotension should make you worry about potentially deadly diagnoses
  • Perform a careful physical exam
    • Undressing the patient to fully examine the trunk and the extremities
    • Look at palms, soles and mucous membranes
    • Touch the skin with a gloved hand to determine if the lesions are flat or raised
    • Press on lesions to see whether they blanch
    • Rub erythematous skin to see if it sloughs

Differential Diagnosis


Vesiculobullous rashes



Necrotizing rashes

Petechiae/Purpura (by cause)

Erythematous rash

Dark raised skin lesions


Algorithm for the Evaluation of Dermatologic Emergencies

Rash visual diagnosis

Erythematous rash

Vesiculobullous rashes visual diagnosis

Dark raised skin lesions


  • Based on diagnosis


  • Based on diagnosis

See Also

External Links


  1. Nguyen T and Freedman J. Dermatologic Emergencies: Diagnosing and Managing Life-Threatening Rashes. Emergency Medicine Practice. September 2002 volume 4 no 9.