Rash

Rash is a common presenting symptom with many different causes. A systematic approach is necessary to identify life-threatening conditions and reach a definitive diagnosis. Initial management steps include evaluating for red flags for a life-threatening rash and characterizing the rash based on its basic morphology, e.g., petechial or purpuric, erythematous, maculopapular, annular, or vesiculobullous. The cause of rash can often be identified clinically, but specific testing may be required based on the presumptive diagnosis. Management is specific to the condition. Although most rashes can affect individuals of any age, some are more common in childhood (e.g., pediatric viral exanthems).

For details on rashes or lesions due to localized infection, see “Overview of skin and soft tissue infections.”

Petechial and purpuric rashes

Febrile or severely ill patients

• Palpable lesion
  • Meningococcal septicemia
  • Disseminated gonococcal infection
  • Acute bacterial endocarditis
  • Rocky Mountain spotted fever (RMSF)
  • IgA vasculitis
• Nonpalpable lesion
  • Thrombotic thrombocytopenic purpura (TTP)
  • Purpura fulminans
  • Acute leukemia ^[3]

Afebrile patients

• Palpable lesion: vasculitis
• Nonpalpable lesion: idiopathic thrombocytopenia (ITP)

Erythematous rashes

Febrile or severely ill patients

• Positive Nikolsky sign
  • Staphylococcal scalded skin syndrome (SSSS)
  • Stevens-Johnson syndrome (SJS)
  • Toxic epidermal necrolysis (TEN)
• Negative Nikolsky sign
  • Toxic shock syndrome (TSS)
  • Kawasaki disease
  • Scarlet fever

Afebrile patients

• Positive Nikolsky sign: Toxic epidermal necrolysis
• Negative Nikolsky sign
  • Anaphylaxis
  • Histamine fish poisoning
  • Medication flushing syndrome, e.g., vancomycin, niacin
  • Alcohol flush reaction

Maculopapular rashes

Febrile or severely ill patients

• Central distribution
  • Measles
  • Viral exanthem
  • Lyme disease
  • Drug reaction with eosinophilia and systemic symptoms (DRESS syndrome)
• Peripheral distribution
  • Erythema multiforme
  • Meningococcal septicemia
  • RMSF
  • Syphilis
  • Lyme disease

Afebrile patients

• Central distribution
  • Drug reaction
  • Pityriasis rosea
• Peripheral distribution
  • Scabies
  • Atopic dermatitis
  • Bed bugs ^[4]

Vesiculobullous rashes

See “Overview of blistering skin diseases.”

Febrile or severely ill patients

• Diffuse distribution
  • Varicella
  • Disseminated intravascular coagulation (DIC)
  • Disseminated gonococcal infection
  • Smallpox
• Localized distribution
  • Necrotizing fasciitis
  • Hand foot and mouth disease

Afebrile patients

• Diffuse distribution
  • Bullous pemphigoid
  • Pemphigus vulgaris
• Localized distribution
  • Herpes zoster
  • Contact dermatitis
  • Burns
  • Dyshidrotic eczema

Annular skin lesions ^[5]

• Tinea infections
• Nummular dermatitis
• Erythema marginatum
• Erythema multiforme
• Fixed drug eruption
• Granuloma annulare
• Subacute cutaneous lupus erythematosus

Skin plaques and scaling lesions ^[6]

• Psoriasis
• Seborrheic dermatitis
• Cutaneous lichen planus
• Pityriasis rubra pilaris
• Mycosis fungoides
• Erythroderma
• Tinea infections
• See also “Differential diagnosis of scaling.”

Urticaria ^[7]

See also “Type I hypersensitivity reaction.”

• Acute (< 6 weeks): viral infection, drug reactions, or food allergens
• Chronic (≥ 6 weeks)
  • Spontaneous urticaria
  • Chronic inducible urticaria

Childhood rashes ^[8][9]

See also “Differential diagnosis of infectious rashes in childhood.”

Common causes

• Roseola infantum
• Pityriasis rosea
• Scarlet fever
• Erythema infectiosum
• Hand foot and mouth disease
• Nonbullous impetigo
• Atopic dermatitis
• Contact dermatitis
• Exanthematous cutaneous reaction ^[10][11]
• Scabies
• Tinea infections

Less common causes

• Varicella zoster (chickenpox)
• Measles
• Rubella
• Erysipelas
• SSSS
• SJS/TEN
• Acute generalized exanthematous pustulosis
• DRESS
• RMSF

Approach ^[1][2][12]

• Don PPE.
• Obtain vital signs.
• Isolate patients with fever and petechial rash and use droplet precautions.
• Identify patients with red flags for a life-threatening rash.
  • Initiate continuous monitoring and place IV access in severely ill patients.
  • Consult dermatology urgently.
• Initiate treatment for life-threatening causes of rash immediately.
• Perform a focused clinical evaluation.
• Narrow the differential diagnosis based on the morphology of the rash (see “Etiology”).
• Obtain appropriate diagnostic testing.
• Begin supportive and definitive treatment.

Red flags for a life-threatening rash ^[2]

• Fever
• Severely ill appearance, e.g., lethargy, cyanosis, mottled extremities, hypoventilation or hyperventilation
• Hypotension
• Mucosal lesions
• Severe pain
• Extremes of age
• History of immunosuppression
• Recently initiated medication

Life-threatening causes of rash

• Pemphigus vulgaris
• SJS/TEN
• DRESS
• TSS
• Meningococcal septicemia
• RMSF
• Necrotizing fasciitis

Disposition ^[4]

Admit patients with any of the following:

• Hypotension
• High fever or hypothermia
• Systemic infection or underlying condition requiring inpatient management
• Significant fluid and electrolyte abnormalities
• Inability to maintain oral intake

The differential diagnosis of a rash can be quickly narrowed using basic morphology and associated clinical findings. ^[1][2]

Focused history ^[2][8][12]

Rash characteristics

• Onset
• Duration
• Progression

Associated symptoms

• Fever
• Pruritus
• Pain at rash site
• Arthralgias

Exposures

• New medications
• Recent travel
• Occupation
• Change in personal care products
• Sexual history
• Sick contacts
• Recent bites

Focused examination ^[2][4][12]

General physical examination

• Overall condition, e.g., mental status and vital signs
• Lung auscultation
• Cardiac auscultation
• Lymphadenopathy

Skin examination

See “Primary skin lesions” and “Secondary skin lesions” for describing and documenting rashes.

• Rash morphology
  • Petechiae or purpura
  • Erythema
  • Maculopapular rash
  • Vesiculobullous rash
• Lesion characteristics
  • Palpable or nonpalpable
  • Blanchable
  • Positive or negative Nikolsky sign

Always have the patient disrobe and ensure that the entire body is examined, including mucus membranes and genitalia.

Laboratory studies ^[4][12]

Routine laboratory studies are seldom required for rashes that appear benign, but are necessary in severely ill patients.

• CBC
  • Thrombocytopenia, e.g., in vasculitis
  • Leukocytosis suggests infection or severe inflammatory disease.
• CMP
  • Electrolyte and acid-base abnormalities suggest severe disease.
  • Abnormal LFTs may indicate hepatitis, e.g., in severe drug reactions.
• Serology, antibody, and antigen testing
  • Rapid strep test: often positive in scarlet fever
  • EBV serology: positive in infectious mononucleosis
  • Monospot test: positive in infectious mononucleosis, but may be false positive
  • VDRL or FTA-ABS: diagnostic for syphilis
  • Rickettsia antibody panels
  • Lyme antibody testing
  • ANCA: for suspected autoimmune conditions, e.g., eosinophilic granulomatosis with polyangiitis
• Cultures: CSF for meningococcal septicemia, blood cultures for endocarditis

Dermatologic studies

• Punch biopsy: for uncertain diagnosis or suspected autoimmune condition
• Tzanck smear: in vesicular lesions; diagnostic for pemphigus vulgaris, HSV infection, and chickenpox
• Vesicle or pustule cultures: for suspected bacterial, fungal, or viral infections
• Patch test: for suspected contact dermatitis, allergic dermatitis
• KOH prep: for suspected fungal infections

The lesions of a petechial or purpuric rash do not blanch when pressure is applied.

Common causes of petechial and purpuric rashes [2][3][13]
	Images	Distinguishing features	Diagnostic findings	Management
Meningococcal septicemia		Palpable rash Fever Symptoms of meningitis [3]	Positive CSF and/or blood cultures	Immediate stabilization for meningitis, isolation precautions Immediate empiric antibiotics for bacterial meningitis See “Management of meningitis.”
Acute bacterial endocarditis		Palpable rash High fever Malaise, fatigue Splinter hemorrhages Janeway lesions Osler nodes Cardiac murmur	Valve lesion on echocardiogram Positive blood cultures	Empiric antibiotic therapy for infective endocarditis See “Management of infective endocarditis.”
RMSF		Palpable rash Fever Headaches Myalgias	Clinical diagnosis supported by laboratory studies [14]	Immediate empiric antibiotic therapy See “Treatment” in “RMSF.”
Disseminated gonococcal infection		Palpable rash Fever Arthralgias Petechiae that progress to pustules	Positive culture from blood, urethral, cervix, and/or skin lesion	Antibiotic therapy for gonorrhea See “Management of gonorrhea.”
IgA vasculitis		Palpable rash Fever Arthralgias Abdominal pain	Clinical diagnosis supported by laboratory studies Findings indicating nephritis	Fluid therapy Glucocorticoids, IVIg See “Treatment of IgA vasculitis.”
TTP		Nonpalpable rash Fever Altered mental status Signs of hemolytic anemia	CBC: ↓ platelets, ↓ hemoglobin Coagulation studies: normal pTT Urinalysis: hematuria, proteinuria	Hematology consult Plasma exchange See “Treatment of TTP.”
ITP		Nonpalpable rash No fever Mild mucosal or cutaneous bleeding	Thrombocytopenia	Glucocorticoids, IVIg See “Treatment of ITP.”
Vasculitic syndromes		Palpable rash Patients are often afebrile and appear well.	Thrombocytopenia ↑ ESR and CRP	Immunosuppressive therapy See “Vasculitides.”

Unexplained purpura in a child, especially on the trunk, ears, or face, may indicate child abuse. ^[3]

Erythematous rashes manifest as diffuse redness that blanches with pressure.

Common causes of erythematous rashes [2][4]
	Images	Distinguishing features	Diagnostic findings	Management
SSSS		Fever Patient appears severely ill. Tender rash, later bullous Positive Nikolsky sign	Leukocytosis Findings of organ failure on CMP Positive blood cultures and/or cultures from the suspected source of infection	Fluid therapy Empiric antibiotics See “Management of SSSS.”
TEN and SJS [15]		Fever is common. Patient appears severely ill. Mucus membrane involvement Evolves to bullous rash over 5–7 days Positive Nikolsky sign Designation depends on body surface area involvement: < 10%: SJS 10–30%: SJS/TEN > 30%: TEN	Leukocytosis Findings of organ failure on CMP Characteristic features on skin biopsy	Discontinue offending medications. Initiate burn management. Consider transfer to a burn center. See “Treatment of SJS and TEN.”
TSS		Fever Signs of shock Nonexudative mucosal inflammation Negative Nikolsky sign Desquamation occurs after several days.	Diagnostic findings of sepsis	Immediate hemodynamic support Empiric antibiotic therapy for TSS See “Management of TSS.”
Scarlet fever rash		Fever Malaise Sore throat Negative Nikolsky sign Fine papules	Positive rapid strep test Throat culture	Empiric antibiotics See “Management of scarlet fever.”
Anaphylaxis		Features of anaphylaxis No fever Negative Nikolsky sign	Clinical diagnosis Elevated serum tryptase	IV or IM epinephrine IV fluid resuscitation See “Management of anaphylaxis.”
Histamine fish poisoning [16]		History of ingesting dark-meat fish No fever Pruritus and urticaria Burning sensation in mouth Negative Nikolsky sign	Clinical diagnosis	Antihistamines Epinephrine (if symptoms are severe) See “Histamine fish poisoning.”
Flushing reaction [17][18]		Previous exposure to alcohol or a triggering drug, e.g., vancomycin, niacin No fever Negative Nikolsky sign Pruritus	Clinical diagnosis	Antihistamines Discontinue or slow infusion of triggering medication.

The mixture of flat and raised discolored areas that define a maculopapular rash may also be the early stage of a petechial, purpuric, or vesiculobullous rash.

Common causes of maculopapular rashes [2][4]
	Images	Distinguishing features	Diagnostic findings	Management
Measles		Prodrome of fever and malaise “3 Cs”: cough, coryza, and conjunctivitis Blanching rash Koplik spots	Positive measles serology and/or PCR	Respiratory and contact isolation Supportive therapy Vitamin A supplementation See “Management of measles.”
Kawasaki disease		Fever Cervical lymphadenopathy Conjunctival injection Strawberry tongue Peripheral edema	↑ Inflammatory markers Variable ECG changes	IVIg Aspirin See “Management of Kawasaki disease.”
Secondary syphilis		Diffuse reddish-brown or copper lesions on the trunk and extremities Potentially fever and/or malaise Occurs weeks to months after resolution of the initial chancre	Positive nontreponemal tests, e.g., RPR, VDRL Positive treponemal tests, e.g., FTA-ABS	Antibiotics for syphilis See “Treatment of syphilis.”
Viral exanthem		Variable presentation Typically nonpruritic Does not desquamate	Typically a clinical diagnosis	See “Infectious rashes in childhood.”
Cutaneous drug reactions [10][11]		Usually pruritic Begin on the trunk and spread to the extremities Symmetrical distribution	Clinical diagnosis	Discontinue inciting medication. Antihistamines
Scabies		Elongated papules Typically affects interdigital folds, intertriginous areas, and wrists Pruritic	Dermoscopic visualization of mites, larvae, ova, or mite feces	Scabicidal agents See “Treatment of scabies.”
Atopic dermatitis		Dry, scaly rash Infants: cheeks, scalp, extensor areas Children and adults: antecubital fossa, extensor areas Intense pruritus	Clinical diagnosis	Topical emollients Topical corticosteroids See “Treatment of atopic dermatitis.”
Pityriasis rosea	Pityriasis rosea may appear as an annular lesion or in a maculopapular distribution; see “Annular skin lesions.”

Meningococcal septicemia, RMSF, and Stevens-Johnson syndrome are life-threatening conditions that may also cause a maculopapular rash.

Vesiculobullous rashes are composed of multiple fluid-filled lesions caused by a disorder of the epidermal-dermal junction.

Common causes of vesiculobullous rashes [2][4]
	Images	Distinguishing features	Diagnostic findings	Management
Varicella		Prodrome of fever, malaise, pharyngitis Macules, papules, and vesicles, simultaneously Spares hands and feet	Clinical diagnosis Positive PCR	Antihistamines Antiviral therapy for VZV infection (only for patients at high risk) See “Treatment for chickenpox.”
Shingles		Grouped vesicles with a dermatomal distribution Severely painful Most common in adults 50–70 years of age	Clinical diagnosis Positive PCR	Respiratory and contact isolation Early and mild: oral antiviral therapy for herpes zoster Severe: IV acyclovir See “Management of shingles.”
Necrotizing fasciitis [19]		Fever Patient appears severely ill Erythema of underlying skin Pain out of proportion to findings	Diagnostic findings of sepsis Positive tissue and fluid cultures	Emergent surgical debridement Empiric antibiotic therapy for skin and soft tissue infections See “Treatment” in “Necrotizing soft tissue infections.”
Hand, foot, and mouth disease [20]		Fever Malaise and anorexia Rash primarily on the hands and feet Painful oral ulcers	Clinical diagnosis	Supportive care for symptom relief
Bullous pemphigoid [21][22]		Diffuse large and tense vesicles Pruritic Prodrome of papular or urticarial lesions Negative Nikolsky sign	Positive serology, immunofluorescence assay, and/or histopathology	Mild: topical corticosteroids Severe: systemic corticosteroids See “Bullous pemphigoid.”
Pemphigus vulgaris [21][22]		Small flaccid and superficial bullae Ruptured bullae coalesce into large erosions. Oral lesions are common. Painful but not pruritic Positive Nikolsky sign	Positive serology, immunofluorescence assay, and/or histopathology	IV fluid resuscitation Wound care similar to burn management Systemic corticosteroids See “Pemphigus vulgaris.”
Bullous impetigo		Large thin-walled bullae Thin serous crust after rupture Most commonly affects the trunk and extremities Negative Nikolsky sign	Clinical diagnosis	Antibiotic therapy See “Management of impetigo.”
Contact dermatitis		History of exposure to a possible offending agent Distinct rash borders Pruritic	Clinical diagnosis Patch testing (if diagnosis is uncertain)	Mild: topical corticosteroids Severe: systemic corticosteroids See “Treatment of contact dermatitis.”

See also “Autoimmune blistering diseases” and “Skin and soft tissue infections.”

Disseminated gonococcal infection, acute generalized exanthematous pustulosis, and smallpox may have a vesiculobullous appearance.

• Don PPE.
• Obtain vital signs including temperature.
• Place patients with fever and petechial rash in respiratory and contact isolation.
• Rapidly identify red flags for a life-threatening rash.
  • Initiate continuous monitoring and place IV access in toxic-appearing patients.
  • Consult dermatology urgently.
• Perform a focused clinical evaluation.
• Obtain appropriate diagnostic testing.
• Begin supportive and definitive treatment.
• Admit patients with any of the following:
  • Hypotension
  • High fever or hypothermia
  • Systemic infection or underlying condition requiring inpatient management
  • Significant fluid and electrolyte abnormalities
  • Inability to maintain oral intake

Skin nodules ^[23][24]

A skin nodule is an elevated cystic or solid lesion > 1 cm in diameter.

• Sebaceous hyperplasia
• Epidermal inclusion cysts
• Dermatofibroma
• Acrochordon
• Rheumatoid nodules
• Nonmelanoma skin cancer
• Chancre
• Leprosy

Cutaneous ulcers ^[25]

Cutaneous ulcers are rounded or irregularly shaped discontinuities in the skin caused by loss of the epidermis and some portion of the dermis.

• Chronic venous disease
• Peripheral artery disease
• Collagen vascular disease
• Vasculitides
• Pyoderma gangrenosum
• Necrobiosis lipoidica
• Decubitus ulcer