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
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
- 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.
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
- Aggravating and alleviating factors
- Associated symptoms:
- Other pertinent history:
- Recent travel
- Insect, plant, or animal exposure
- Occupational history
- New home products
- Drug exposure
- Sick contacts
- Chronic illnesses
- Sexual history
|Patient’s history||Associated disease|
|Contact with ill persons|
|Occupational or environmental exposure||Contact dermatitis|
|Insect and arthropod exposure|
|Recent systemic symptoms|
A full skin exam should be performed.
- Number of lesions
- Configuration and borders
- Presence of scale or crusts
- Diffuse or localized
- Symmetrical or asymmetrical
- Clustered or grouped
- Mucosal involvement
- Atypical sites (e.g., palms and soles)
- Palpation of lesions:
- Texture changes
- 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
- Heart murmur
- 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
- Skin moisturizers
- Symptom management for pain and pruritis:
- For inflammatory conditions:
- Infection should be ruled out.
- Topical steroids:
- Systemic steroids
- For infectious causes:
- Appropriate management for underlying systemic conditions
Comparison of Generalized Rashes
|Atopic dermatitis (eczema)|
|Pityriasis rosea||Clinical diagnosis|
|Lichen planus||Topical steroids|
EM: erythema multiforme
SJS: Stevens-Johnson syndrome
TEN: toxic epidermal necrolysis
|Hand-foot-and-mouth disease||Clinical diagnosis||Symptomatic treatment|
|Roseola infantum (exanthem subitum)||Clinical diagnosis||Symptomatic treatment|
|Measles (rubeola)||Clinical diagnosis||Symptomatic treatment|
|Rubella (German measles)||Symptomatic treatment|
|5th disease (erythema infectiosum)||Symptomatic treatment|
PCR: polymerase chain reaction
Comparison of Common Localized Rashes
|Tinea corporis||Topical or oral antifungals|
|Herpes zoster (shingles)|
MRSA: methicillin-resistant S. aureus
ESR: erythrocyte sedimentation rate
KOH: potassium hydroxide
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