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]

Dermatology Nomenclature

Small lesions (<0.5cm)

Name Raised/Palpable Fluid-Filled Other Description Diagram
MaculeNoNoneflat, cirumscribed, colored
PustuleYesPusLeukocytes or keratin

Large lesions (>0.5cm)

Name Raised/Palpable Fluid-Filled Other Description Diagram
PatchNoNoneLarge macule (flat, colored)
PlaqueYesNoneSuperficially raised, circumscribed solid area
NoduleYesNoneDistinct large papule
BullaYesClearLarge vesicle/blister or exposed epidermal layer
WhealYesEdemaFirm and edema of dermis


  • Plaque/scaley papule
  • Eschar
  • Fissure/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


Rash visual diagnosis

Erythematous rash

Vesiculobullous rashes visual diagnosis

Dark raised skin lesions


  • Based on diagnosis


  • Based on diagnosis

See Also


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