Overview
Definition
A rash is an abnormal change in the skin’s color or texture.
Epidemiology
- 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.
Etiology
The list of etiologies for rashes is long but can include irritants, allergens, infections, and inflammatory conditions.
Classification
Rashes are described and classified based on certain characteristics, which can assist with forming a differential diagnosis when evaluating a patient.
Configuration
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
Visualization of different rash configurations
Image by Lecturio.Morphology
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
Visualization of different rash morphologies
Image by Lecturio.
Schematic to help differentiate different morphologies based on their size and characteristics
Image by Lecturio.
Small, flat macules due to rubella
Image: “Rubella” by CDC. License: Public Domain
Large patches of hypopigmentation in vitiligo
Image: “Split thickness skin grafting in patients with stable vitiligo” by Sameem F, Sultan SJ, Ahmad QM. License: CC BY 2.0
Multiple skin papules on the hands
Image: “Generalized lichen nitidus in childhood” by Mehta V, Balachandran C. License: CC BY 2.0
Skin plaques from psoriasis
Image: “Pulmonary sarcoidosis associated with psoriasis vulgaris: coincidental occurrence or causal association? Case report” by Nikolopoulou M, Katsenos S, Psathakis K, Rallis E, Sampaziotis D, Panagou P, Tsintiris K, Bouros D. License: CC BY 2.0
A large skin nodule
Image: “Ovarian carcinoma presenting as cutaneous nasal metastasis” by Anais Brasileiros de Dermatologia. License: CC BY 4.0
Multiple vesicles on the neck due to shingles
Image: “Herpes Zoster am Hals” by M.S. License: Public Domain
Several wheals due to skin testing for allergies
Image: “Autologous serum skin test in children” by Godse KV. License: CC BY 2.0
Picture of multiple pustules (pus-filled blisters)
Image: “A rare presentation of pemphigus vulgaris as multiple pustules” by Yang Y, Lin M, Huang SJ, Min C, Liao WQ. License: CC BY 2.0
Tense bulla on the dorsum of the 2nd toe and a larger collapsed bulla on the ball of the great toe
Image: “Bullosis diabeticorum: A distinctive blistering eruption in diabetes mellitus” by Ghosh SK, Bandyopadhyay D, Chatterjee G. License: CC BY 2.0
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
An overlying crust
Image: “Diabetic dermopathy (“shin spots”) and diabetic bullae (“bullosis diabeticorum”) at the same patient” by Brzezinski P, Chiriac AE, Pinteala T, Foia L, Chiriac A. License: CCC BY 3.0
Scale on a herald patch of pityriasis rosea
Image: “Pityriasis rosea” by CDC. License: Public Domain
Thick, leathery skin (lichenification) due to eczema
Image: “Clinical Characteristics, Treatments, and Prognosis of Atopic Eczema in the Elderly” by Tanei R. License: CC BY 4.0
Distribution
- 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.
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.
History
- 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
| Patient’s history | Associated disease |
|---|---|
| Chronic illness |
|
| Contact with ill persons |
|
| Drug exposure |
|
| Occupational or environmental exposure | Contact dermatitis |
| Insect and arthropod exposure |
|
| Recent systemic symptoms |
|
| Sexual history |
|
| Travel |
|
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
Testing
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
Management
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
| Condition | Features | Diagnosis | Management |
|---|---|---|---|
| Atopic dermatitis (eczema) |
|
|
|
| Drug eruption |
|
|
|
| Pityriasis rosea |
| Clinical diagnosis |
|
| Lichen planus |
|
| Topical steroids |
| Psoriasis |
|
| Local therapy:
|
EM: erythema multiforme
SJS: Stevens-Johnson syndrome
TEN: toxic epidermal necrolysis
Erythema and lichenification in the kneefolds of a patient with atopic dermatitis
Image: “Role of the skin microbiome in atopic dermatitis” by Salava A, Lauerma A. License: CC BY 4.0
Edematous wheals suggestive of urticaria. This can be a manifestation of a drug eruption.
Image: “Urticaria and angioedema” by Kanani A, Schellenberg R, Warrington R. License: CC BY 2.0
Target lesions of erythema multiforme, which may be a manifestation of a drug eruption
Image: “Erythema multiforme as first sign of incomplete Kawasaki disease” by Vierucci F, Tuoni C, Moscuzza F, Saggese G, Consolini R. License: CC BY 2.0, edited by Lecturio.
Drug-induced toxic epidermal necrolysis with peeled skin over the back and buttocks
Image: “Drug induced toxic epidermal necrolysis: two case reports.” by Qadir SN, Raza N, Qadir F. License: CC BY 3.0
The secondary, generalized eruption of pityriasis rosea:
Image: “Pityriasis rosea” by Aceofhearts1968. License: Public Domain
Multiple small, pink lesions are seen. Their oblique positioning is due to their orientation along Langer’s lines. In some patients, this can give a “Christmas tree” appearance.
Lichen planus located on the upper thigh. Notice the common characteristics of these lesions: polygonal in shape, purple/violaceous in color, and planar. Primary lesions are often a few millimeters in size but can coalesce in larger plaques and are often pruritic.
Image: “12188” by CDC/ Wallace N. McLeod, M.D.; Bob Craig. License: Public Domain
Psoriatic lesion on the knee
Image: “Myelin-associated glycoprotein-related neuropathy associated with psoriasis: a case report” by Murata KY, Miwa H, Kondo T. License: CC BY 2.0
Infectious conditions
| Condition | Features | Diagnosis | Management |
|---|---|---|---|
| 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 |
| Scarlet fever |
|
|
|
| Chickenpox |
|
|
|
PCR: polymerase chain reaction
Painful vesicles on a hand (A) and foot (B) due to hand-foot-and-mouth disease
Image: “Hand, foot and mouth disease: changing Indian scenario” by Rao PK, Veena K, Jagadishchandra H, Bhat SS, Shetty SR. License: CC BY 3.0, edited by Lecturio.
Diffuse maculopapular rash on the chest and abdomen due to roseola infantum
Image: “Sestamalattia” by Emiliano Burzagli. License: Public Domain
Maculopapular rash on the face of a child with measles
Image: “Measles child Philippines” by Jim Goodson. License: Public Domain
Macular rash of rubella on the skin of a child’s back
Image: “ଫାଇଲ:Rash of rubella on back (crop)” by CDC. License: Public Domain
Pediatric patient with 5th disease: erythematous facial rash accompanied by rash on the torso and extremities
Image: “Fifth disease” by Andrew Kerr. License: Public Domain
Face looks flushed but with “white mustache” or circumoral pallor, typical of scarlet fever.
Image: “Slapped cheeks and white mustache” by Estreya. License: CC BY-SA 4.0
Diffuse vesicles on a red base due to chickenpox
Image: “21501” by K.L. Herrmann. License: Public Domain
Comparison of Common Localized Rashes
| Condition | Features | Diagnosis | Management |
|---|---|---|---|
| Contact dermatitis |
|
|
|
| Tinea corporis |
|
| Topical or oral antifungals |
| Seborrheic dermatitis |
|
|
|
| Impetigo |
|
|
|
| Cellulitis |
|
|
|
| Erysipelas |
|
|
|
| Necrotizing fasciitis |
|
|
|
| Herpes zoster (shingles) |
|
|
|
MRSA: methicillin-resistant S. aureus
ESR: erythrocyte sedimentation rate
KOH: potassium hydroxide
A pruritic, vesicular eruption due to contact dermatitis
Image: “Neoprene Orthopaedic Supports: An Underrecognised Cause of Allergic Contact Dermatitis” by Hawkey S, Ghaffar S. License: CC BY 3.0
Annular, scaling lesion of tinea corporis
Image: “Ringworm on the arm, or tinea corporis due to Trichophyton mentagrophytes PHIL 2938 lores” by /Dr. Lucille K.. License: Public Domain
Seborrheic dermatitis in a renal transplant recipient.
Image: “Inflammatory Cutaneous Diseases in Renal Transplant Recipients” by International Journal of Molecular Sciences. License: CC BY 4.0
Note the erythematous scaly papules on the chin and nasolabial folds.
Crusted, non-bullous impetigo on the upper extremity of a pediatric patient
Image: “Diagnosis of Atopic Dermatitis: Mimics, Overlaps, and Complications” by Siegfried EC, Hebert AA. License: CC BY 4.0
Photograph showing marked pitting edema and erythema with poorly demarcated borders due to cellulitis
Image: “How 40 kilograms of fluid retention can be overlooked: two case reports” by Ong HS, Sze CW, Koh TW, Coppack SW. License: CC BY 2.0
Facial erysipelas presenting as an erythematous and edematous plaque covering the cheeks and nose with the presence of excoriations and vesicles.
Image: “Facial erysipelas” by Dr. Thomas F. Sellers. License: Public Domain
Compared with cellulitis, this rash is well demarcated with raised borders.
Cutaneous necrosis, erythema, and bullous changes due to necrotizing fasciitis of the leg
Image: “Necrotizing fasciitis left leg” by Piotr Smuszkiewicz, Iwona Trojanowska and Hanna Tomczak. License: CC BY 2.0
Vesicular eruption involving the V3 dermatome in shingles
Image: “Facial herpes zoster infection precipitated by surgical manipulation of the trigeminal nerve during exploration of the posterior fossa: a case report” by Mansour N, Kaliaperumal C, Choudhari KA. License: CC BY 3.0
References
- Ely JW, Osheroff JA, Ebell MH, et al. Analysis of questions asked by family doctors regarding patient care. BMJ. 1999;319(7206):358–361.
- Fleischer AB Jr, Feldman SR, McConnell RC. The most common dermatologic problems identified by family physicians, 1990–1994. Fam Med. 1997;29(9):648–652.
- Fleischer AB Jr, Feldman SR, Bullard CN. Patients can accurately identify when they have a dermatologic condition. J Am Acad Dermatol. 1999;41(5 pt 1):784–786.
- Norman GR, Rosenthal D, Brooks LR, Allen SW, Muzzin LJ. The development of expertise in dermatology. Arch Dermatol. 1989;125(8):1063–1068.
- Bircher, A. (2020). Exanthematous (maculopapular) drug eruption. UpToDate. Retrieved Feb 10, 2021, from https://www.uptodate.com/contents/exanthematous-maculopapular-drug-eruption
- Armstrong, C.A. (2021). Approach to the clinical dermatologic diagnosis. In Corona, R. (Ed.), UpToDate. Retrieved February 26, 2021, from https://www.uptodate.com/contents/approach-to-the-clinical-dermatologic-diagnosis
- Bickers DR, Lim HW, Margolis D, Weinstock MA, Goodman C, Faulkner E et al. (2006). The burden of skin diseases: 2004 a joint project of the American Academy of Dermatology Association and the Society for Investigative Dermatology. Journal of the American Academy of Dermatology 55:490-500.
- Ely, J. and Stone, M. (2010). The Generalized Rash: Part I. Differential Diagnosis. American Family Physician. 81(6):726-734.
- Ely, J. and Stone, M. (2010) The Generalized Rash: Part II. Diagnostic Approach. American Family Physician. 81(6):735-739.
