General approach to rashes

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


3D medical illustration showing major layers of skin
  • 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
Macule No None flat, cirumscribed, colored Macule.png
Papule Yes None Solid Papule.png
Vesicle Yes Clear Vesicles (2).png
Pustule Yes Pus Leukocytes or keratin Pustules.png

Large lesions (>0.5cm)

Name Raised/Palpable Fluid-Filled Other Description Diagram
Patch No None Large macule (flat, colored) Patch.png
Plaque Yes None Superficially raised, circumscribed solid area Plaque.png
Nodule Yes None Distinct large papule Nodules.png.png
Bulla Yes Clear Large vesicle/blister or exposed epidermal layer Bulla.png
Wheal Yes Edema Firm and edema of dermis


Ulcer, fissue, and erosion

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

Maculopapular rashes

Vesiculobullous rashes



Necrotizing rashes

Petechiae/Purpura (by cause)

Erythematous rash

Dark raised skin lesions

Other Rash



Algorithm for the Evaluation of Dermatologic Emergencies

Maculopapular rashes visual diagnosis

Vesiculobullous rashes visual diagnosis

Erythematous rash

Purpural Rash

Dark raised skin lesions

Other Rash visual diagnosis


  • 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.