Generalized and Localized Rashes

Rashes are a group of diseases that cause abnormal coloration and texture to the skin. The etiologies are numerous but can include irritation, allergens, infections, or inflammatory conditions. Rashes that present in only 1 area of the body are called localized rashes. Generalized rashes occur diffusely throughout the body. Rashes can be classified by their distribution, configuration, and morphology. The diagnosis is often clinical and based on the patient’s history and physical exam findings. Management is dependent on identifying the correct condition and varies depending on the etiology.

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A rash is an abnormal change in the skin’s color or texture.


  • One of the most common conditions encountered by primary care physicians
  • In 2016, 1 in 4 people in the United States (84.5 million) were affected by skin disease.
  • 1 in 3 people required a dermatology evaluation.
  • Maculopapular rashes are the most commonly seen generalized rash (95%).
  • Diagnostic errors in generalized rashes are common.


The list of etiologies for rashes is long but can include irritants, allergens, infections, and inflammatory conditions.


Rashes are described and classified based on certain characteristics, which can assist with forming a differential diagnosis when evaluating a patient.


The configuration refers to the shape or outline of lesions.  

  • Circinate: round, circular
  • Arciform: forms a partial circle
  • Linear: appears straight 
  • Serpiginous: meandering appearance
  • Annular: round or circular with central clearing  
  • Target: a series of concentric rings 
  • Gyrate: a series of connecting arcs  
  • Zosteriform: appears to follow a dermatome
Rash configurations

Visualization of different rash configurations

Image by Lecturio.


The morphology is based on the size and consistency of the lesions.

  • Flat lesions:
    • Macule: nonpalpable lesion < 1 cm in diameter
    • Patch: nonpalpable lesion > 1 cm in diameter
  • Raised lesions:
    • Papule: elevated lesion < 1 cm in diameter
    • Plaque: flat-topped elevated lesion > 1 cm in diameter
    • Nodule: deep, solid or cystic, elevated lesion > 1 cm in diameter 
    • Wheal: irregularly shaped, edematous, raised, transient plaque
  • Blistering lesions:
    • Vesicle: blister filled with clear fluid, < 1 cm diameter
    • Bulla: blister filled with fluid, > 1 cm diameter
    • Pustule: blister filled with pus
  • Disruption of the epidermis:
    • Erosion: partial-thickness loss of the epidermis
    • Fissure: a crack or split that extends into the dermis
    • Ulcer: full-thickness loss of the epidermis that extends into the dermis
Rash morphology

Visualization of different rash morphologies

Image by Lecturio.
Rash morphology flowchart

Schematic to help differentiate different morphologies based on their size and characteristics

Image by Lecturio.

Secondary characteristics

  • Crust: dried exudate on the skin
  • Scale: flakes or plates of desiccated epidermis
  • Lichenification: leathery thickening of the skin with exaggerated skin markings
  • Excoriation: linear skin erosions, often caused by scratching
  • Edema: swelling of the tissue
  • Scar: fibrous tissue development after an injury


  • Localized: Lesions are confined to a specific area.
  • Generalized: Lesions are dispersed throughout the body.
  • Symmetric: similarly affects both sides of the body
  • Asymmetric: unilateral or affects both sides of the body differently
  • Discrete: separate, distinct lesions
  • Grouped: clusters of lesions
  • Confluent (coalescing): Smaller lesions merge together.
  • Cleavage plane: Lesions are arranged along the lines of skin tension.
Rash distribution

Visualization of different rash distributions

Image by Lecturio.

Clinical Presentation and Diagnosis

The diagnosis for many conditions is purely clinical and based on the patient’s history and physical exam.


  • Onset (including the location of initial onset)
  • Time frame:
    • Acute or chronic
    • Relapsing-remitting
  • Progression
  • Aggravating and alleviating factors
  • Associated symptoms:
    • Fever
    • Pruritus
    • Pain
    • Malaise
    • Cough
  • Other pertinent history: 
    • Allergies
    • Recent travel
    • Insect, plant, or animal exposure
    • Occupational history
    • New home products
    • Drug exposure
    • Sick contacts
    • Chronic illnesses
    • Sexual history
Table: Summary of possible conditions based on patient’s history
Patient’s historyAssociated disease
Chronic illness
  • Dermatitis herpetiformis
  • Seborrheic dermatitis
Contact with ill persons
  • 5th disease
  • Meningococcemia
  • Rubella
  • Roseola
  • Rubeola
  • Scarlet fever
  • Varicella
Drug exposure
  • Lupus
  • Drug eruption
  • Urticaria
  • Stevens-Johnson syndrome
Occupational or environmental exposureContact dermatitis
Insect and arthropod exposure
  • Insect bites
  • Lyme disease
  • Rickettsialpox
  • Rocky Mountain spotted fever
  • Scabies
Recent systemic symptoms
  • 5th disease
  • HIV acute exanthem
  • Kawasaki disease
  • Meningococcemia
  • Roseola
  • Rubella
  • Rubeola
  • Scarlet fever
  • Varicella
Sexual history
  • HIV acute exanthem
  • Secondary syphilis
  • Disseminated gonorrhea
  • Insect bites
  • Lyme disease
  • Rickettsialpox
  • Rocky Mountain spotted fever
HIV: human immunodeficiency virus

Physical exam

A full skin exam should be performed.

  • Appearance:
    • Number of lesions
    • Configuration and borders
    • Morphology
    • Color
    • Presence of scale or crusts
  • Distribution:
    • Diffuse or localized
    • Symmetrical or asymmetrical
    • Dermatomal
    • Clustered or grouped
    • Mucosal involvement
    • Atypical sites (e.g., palms and soles)
  • Palpation of lesions:
    • Raised
    • Flat
    • Texture changes
    • Induration
    • Blanching with pressure
  • In patients with bullae, check for Nikolsky sign:
    • Extension of skin blistering or sloughing by applying pressure
    • Demonstrates skin detachment
  • In patients with plaques, check for Auspitz sign: pinpoint bleeding after scraping plaques
  • Other physical exam findings to evaluate for:
    • Vital signs
    • Lymphadenopathy
    • Conjunctivitis
    • Pharyngitis
    • Heart murmur
    • Hepatosplenomegaly
    • Joint swelling
    • Neurologic deficits


A diagnostic workup may be performed if the history and physical exam do not provide enough clues to the diagnosis. The differential diagnosis will dictate which studies should be performed.

  • Biopsy with microscopic examination:
    • There are no widely accepted guidelines with indications for skin biopsy.
    • Immunofluorescence can be helpful.
  • Laboratory tests are indicated if there are systemic symptoms.
    • CBC → evaluate for eosinophilia, neutrophilia, or thrombocytopenia
    • Basic metabolic panel and liver function panel → evaluate for systemic renal and hepatic involvement
    • ANAs → a good initial test if an autoimmune etiology is being considered
    • Serologic testing for various infectious causes
  • Allergy testing:
    • Patch testing
    • Skin prick testing
    • Serum IgE studies


The management of a rash depends on the underlying condition. Many rashes will be self-limited and may not require any treatment.

  • Basic management:
    • Identify and avoid aggravating factors.
    • Supportive therapies:
      • Low-heat baths
      • Mild soaps
      • Emollients
      • Skin moisturizers
  • Symptom management for pain and pruritis:
    • Acetaminophen
    • NSAIDs
    • Antihistamines
  • For inflammatory conditions:
    • Infection should be ruled out.
    • Topical steroids:
      • Hydrocortisone
      • Triamcinolone
      • Clobetasol
      • Betamethasone
    • Systemic steroids
  • For infectious causes:
    • Antibiotics
    • Antifungals
    • Antivirals
  • Appropriate management for underlying systemic conditions

Comparison of Generalized Rashes

Noninfectious conditions

Table: Summary of common noninfectious generalized rashes
Atopic dermatitis (eczema)
  • Type IV hypersensitivity reaction
  • Ranges from erythema to lichenification to erythroderma
  • Scaly patches or plaques
  • Pruritus
  • Distribution is typically over flexor surfaces.
  • Clinical diagnosis
  • Serum IgE levels
  • Skin prick tests
  • Patch tests
  • Avoid triggers.
  • Symptomatic therapy
  • Emollients
  • Topical corticosteroids
  • Topical calcineurin inhibitors
  • Phototherapy
  • Immunosuppressants
Drug eruption
  • Often an immune-mediated hypersensitivity reaction
  • Ranges in severity from urticaria and maculopapular eruptions to EM, SJS, and TEN
Lesions may include:
  • Edematous wheals
  • Diffuse maculopapular lesions
  • Target lesions
  • Cutaneous bullae
  • Sloughing of skin and mucosa
  • Systemic symptoms
  • Clinical diagnosis
  • Skin biopsy is rarely needed.
  • Withdrawal of the offending drug
  • Symptomatic therapy
  • Supportive care
Pityriasis rosea
  • Idiopathic
  • Single round, ovoid, salmon-colored patch (“herald patch”)
  • Followed by a widespread exanthem with scale
  • “Christmas tree” distribution on back
  • Pruritus
Clinical diagnosis
  • No intervention is needed.
  • Symptomatic management
Lichen planus
  • Idiopathic
  • Cell-mediated inflammatory disease
  • Flat-topped, papular, purple lesions
  • Pruritus
  • Includes genitalia, nails, scalp, and mucous membranes
  • Clinical diagnosis
  • Biopsy for confirmation
Topical steroids
  • Cell-mediated inflammatory disease
  • Well-circumscribed, salmon-colored plaques
  • Silvery scales
  • Seen on the scalp and extensor surfaces
  • Clinical diagnosis
  • Biopsy is rarely needed.
Local therapy:
  • Topical steroids
  • Calcitriol
  • Topical retinoids
  • Phototherapy
Systemic therapy:
  • Methotrexate
  • Cyclosporine
  • Apremilast
  • Biologic agents
Note: Although pityriasis rosea and lichen planus are considered idiopathic, they have been associated with certain viruses.
EM: erythema multiforme
SJS: Stevens-Johnson syndrome
TEN: toxic epidermal necrolysis

Infectious conditions

Table: Summary of common infectious generalized rashes
Hand-foot-and-mouth disease
  • Caused by coxsackievirus type A
  • Painful oval-shaped vesicles on hands, feet, buttocks, and oral mucosa
  • Associated with fever
Clinical diagnosisSymptomatic treatment
Roseola infantum (exanthem subitum)
  • Caused by HHV-6 or -7
  • Rose-pink maculopapular rash
  • Mostly on the chest and abdomen but the back, face, and extremities can be involved
  • Preceded by high fever and cervical lymphadenopathy
Clinical diagnosisSymptomatic treatment
Measles (rubeola)
  • Caused by the measles virus
  • Maculopapular rash that begins on the face and spreads to the trunk and extremities
  • Koplik spots on the buccal membrane
  • Associated with a high fever, cough, coryza, and conjunctivitis
Clinical diagnosisSymptomatic treatment
Rubella (German measles)
  • Caused by rubella virus
  • Fine, pink macules on the face and neck
  • Becomes pinpoint and spreads to the trunk and extremities
  • Less extensive than measles
  • Forschheimer spots (petechiae on the soft palate)
  • Associated with fever, lymphadenopathy, and conjunctivitis
  • Clinical diagnosis
  • Serologic testing
Symptomatic treatment
5th disease (erythema infectiosum)
  • Caused by parvovirus B19
  • Initial prodromal symptoms
  • “Slapped cheek” rash
  • Followed by a morbilliform rash on the torso and extremities
  • Clinical diagnosis
  • IgM or PCR testing is rarely needed.
Symptomatic treatment
Scarlet fever
  • Caused by Streptococcus pyogenes
  • Begins with fever and sore throat
  • Flushed cheeks
  • Strawberry tongue
  • Sandpaper-like rash on neck, trunk, and extremities
  • Pastia’s lines
  • Clinical diagnosis
  • Rapid antigen or throat culture to confirm
  • Penicillin
  • Amoxicillin
  • Caused by varicella-zoster virus
  • Rash appears in crops and progresses from macules to papules to vesicles on a red base
  • Lesions eventually crust.
  • Intense pruritis
  • Begins on trunk and spreads to the face and extremities
  • Prodrome of fever and malaise
  • Clinical diagnosis
  • Serologic testing may be done to confirm the diagnosis.
  • Symptomatic treatment
  • Consider antiviral therapy (acyclovir).
HHV: human herpesvirus
PCR: polymerase chain reaction

Comparison of Common Localized Rashes

Table: Summary of common localized rashes
Contact dermatitis
  • Type IV hypersensitivity reaction from allergens or irritants
  • Maculopapular or vesicular rash
  • Erythema and swelling
  • Weeping, scaling, or crusting
  • Pruritis or burning pain
  • Clinical diagnosis
  • Patch testing
  • Avoid causative agents.
  • Topical steroids
  • Antihistamines
  • Emollients
Tinea corporis
  • Caused by a dermatophyte infection
  • Annular patches or plaques with raised, scaly borders
  • Expand peripherally
  • Central clearing
  • Pruritis
  • KOH preparation
  • Fungal culture
Topical or oral antifungals
Seborrheic dermatitis
  • Unknown etiology
  • Erythematous, well-demarcated plaques
  • Greasy yellow scales
  • Found on the scalp, face, trunk, and intertriginous areas
  • Clinical diagnosis
  • Biopsy to confirm
  • Topical antifungals
  • Topical steroids
  • Calcineurin inhibitors
  • Keratolytic agents
  • Caused by Staphylococcus aureus and S. pyogenes
  • Evolution of papules to vesicles to pustules
  • Honey-colored crusts
  • Bullous form: large, flaccid bullae
  • Clinical diagnosis
  • Cultures are rarely needed.
  • Mild-to-moderate cases: topical antibiotics
  • Bullous or severe cases: oral antibiotics
  • Bacterial infection of the dermis and subcutaneous tissues
  • Erythema and induration
  • Warm to the touch
  • Poorly demarcated
  • Clinical diagnosis
  • Blood cultures if sepsis is present
  • Penicillins
  • Vancomycin for MRSA
  • A more superficial bacterial infection than cellulitis
  • Involves the upper dermis and superficial lymphatics
  • Well-defined erythema with raised demarcation
  • Pain and tenderness
  • Clinical diagnosis
  • Blood cultures if sepsis is present
  • Penicillins
  • Vancomycin for MRSA
Necrotizing fasciitis
  • Life-threatening bacterial infection of the subcutaneous tissues and fascia
  • Rapidly progressive erythema, swelling, and edema
  • Severe pain
  • Bullae and necrosis
  • Systemic toxicity
  • Clinical diagnosis
  • Blood and tissue culture
  • Imaging studies
  • Surgical debridement
  • Broad-spectrum IV antibiotics
  • Hemodynamic support
Herpes zoster (shingles)
  • Caused by reactivation of the varicella-zoster virus
  • Vesicular eruption in a dermatomal distribution
  • Rash is preceded by pain.
  • Complicated by postherpetic neuralgia
  • Clinical diagnosis
  • PCR
  • Tzanck smear
  • Prevented by vaccine
  • Antiviral agents may reduce duration of symptoms.
  • Symptomatic therapy
IV: intravenous
MRSA: methicillin-resistant S. aureus
PCR: polymerase chain reaction
KOH: potassium hydroxide


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