One-liner#
Evaluate acute rash (<2 weeks) to identify dangerous drug reactions and infections requiring urgent treatment while managing the majority with topical therapy and reassurance.
Quick nav#
- Red flags / send to ED
- Key history
- Focused exam
- Differential (quick pattern recognition)
- Workup
- Initial management
- Management by diagnosis
- Follow-up
- Patient instructions
- Smartphrase snippets
Red flags / send to ED#
- Mucosal involvement (oral, genital, ocular) with skin findings → SJS/TEN
- Skin sloughing or blistering >10% BSA
- Facial swelling, lip/tongue swelling, difficulty breathing → angioedema/anaphylaxis
- Fever + diffuse erythema + hypotension → toxic shock syndrome
- Petechiae/purpura + fever → meningococcemia, vasculitis
- Target lesions + mucosal erosions → Stevens-Johnson syndrome
- Rapidly spreading erythema with systemic toxicity → necrotizing fasciitis
Key history#
Timeline:
- Onset: hours (urticaria, drug reaction) vs days (viral exanthem, contact dermatitis)
- Duration: <2 weeks = acute
- Progression: spreading vs stable vs resolving
Morphology (ask patient to describe):
- “Bumpy” vs “flat” vs “blistery”
- “Itchy” vs “painful” vs “burning”
- Color: red, purple, skin-colored
Distribution:
- Localized (contact) vs generalized (systemic)
- Sun-exposed areas (photosensitivity)
- Intertriginous (candida, intertrigo)
- Dermatomal (zoster)
Exposures (critical):
- New medications in past 2-6 weeks (drug eruption)
- New topicals: soaps, lotions, detergents, cosmetics
- Plants, animals, insects
- Sick contacts (viral exanthem)
- Recent illness (post-viral)
- Occupational/hobby exposures
Associated symptoms:
- Fever (viral, drug reaction, infection)
- Arthralgias (viral, serum sickness-like)
- Sore throat, URI symptoms (viral exanthem)
- Mucosal symptoms (SJS/TEN, EM)
Past history:
- Prior similar rashes
- Atopic history (eczema, asthma, allergies)
- Autoimmune disease
- Immunocompromised status
Focused exam#
- Vitals: fever, tachycardia, hypotension
- General: toxic appearance, signs of systemic illness
- Skin:
- Morphology: macule, papule, plaque, vesicle, pustule, wheal, petechiae, purpura
- Distribution: localized vs generalized, symmetric vs asymmetric
- Configuration: linear (contact), dermatomal (zoster), annular (tinea, erythema migrans)
- Surface: scale, crust, erosion, excoriation
- Nikolsky sign: gentle lateral pressure causes skin sloughing (positive in SJS/TEN, pemphigus)
- Mucous membranes: oral erosions, conjunctival injection, genital lesions
- Lymph nodes: regional vs generalized lymphadenopathy
Differential (quick pattern recognition)#
Common/likely (outpatient)#
| Diagnosis | Keywords patients use | Key clues | Focused exam clues | Initial next step |
|---|---|---|---|---|
| Contact dermatitis | “Touched something,” “itchy where I put lotion,” “new soap” | Linear or geometric pattern; localized to exposure site; intensely pruritic | Vesicles, papules in exposed distribution; sharp borders | Remove offending agent; topical steroid; oral antihistamine |
| Drug eruption (morbilliform) | “Started after new medication,” “all over” | New drug 7-14 days prior; symmetric; starts on trunk | Maculopapular; symmetric; spares palms/soles usually | Stop suspected drug; supportive care; antihistamines |
| Viral exanthem | “Sick last week,” “kids have it too” | Prodrome of fever/URI; sick contacts; self-limited | Maculopapular; starts centrally, spreads outward; non-specific | Supportive care; no testing needed if classic presentation |
| Urticaria (acute) | “Hives,” “welts,” “comes and goes,” “itchy bumps” | Wheals lasting <24 hours; migratory; pruritic | Raised, erythematous, blanching wheals; dermographism | Antihistamines; identify trigger if possible |
| Pityriasis rosea | “Herald patch first,” “Christmas tree pattern” | Herald patch 1-2 weeks before generalized eruption; young adult | Oval salmon-colored patches; collarette scale; follows skin lines | Reassurance; self-limited 6-8 weeks; symptomatic treatment |
| Insect bites | “Bug bites,” “itchy bumps,” “woke up with them” | Grouped lesions; exposed areas; seasonal | Papules, sometimes with central punctum; grouped | Topical steroid; antihistamines; reassurance |
| Tinea corporis | “Ring,” “spreading circle,” “itchy patch” | Annular with central clearing; advancing scaly border | Annular plaque; raised scaly border; central clearing | KOH prep; topical antifungal |
| Scabies | “Itchy at night,” “family members itchy too,” “between fingers” | Intense nocturnal pruritus; household contacts affected; burrows | Papules in web spaces, wrists, waistline; burrows; excoriations | Permethrin 5% cream; treat all household contacts |
Can’t-miss / urgent#
| Diagnosis | Keywords patients use | Key clues | Focused exam clues | Initial next step |
|---|---|---|---|---|
| Stevens-Johnson syndrome/TEN | “Blisters,” “skin peeling,” “mouth sores,” “eye pain” | New drug 1-4 weeks prior; mucosal involvement; fever | Target lesions; skin sloughing; oral/ocular erosions; Nikolsky+ | Stop all suspect drugs; ED immediately; burn unit if >10% BSA |
| DRESS (Drug Reaction with Eosinophilia) | “Swollen face,” “rash everywhere,” “feeling terrible” | Drug 2-8 weeks prior; facial edema; fever; lymphadenopathy | Morbilliform rash; facial edema; lymphadenopathy | Stop drug; CBC with diff (eosinophilia); LFTs; urgent derm |
| Meningococcemia | “Spots that don’t blanch,” “very sick,” “fever” | Rapid onset; petechiae/purpura; toxic appearance | Petechiae progressing to purpura; hypotension; fever | ED immediately; call 911 if unstable |
| Herpes zoster | “Burning,” “one side only,” “blisters in a line” | Dermatomal; prodromal pain; immunocompromised at higher risk | Grouped vesicles on erythematous base; dermatomal | Antivirals within 72 hours; pain management |
| Erythema multiforme major | “Target spots,” “mouth sores” | Often HSV-triggered; target lesions; mucosal involvement | Classic targets (3 zones); oral erosions | Treat underlying HSV if present; supportive care; derm referral |
| Cellulitis with systemic signs | “Red spreading,” “hot,” “fever,” “chills” | Fever; rapidly expanding erythema; portal of entry | Expanding erythema; warmth; tenderness; lymphangitis | Antibiotics; mark borders; close follow-up; ED if toxic |
| Erythema migrans (Lyme) | “Bull’s eye,” “tick bite,” “expanding red circle” | Tick exposure; endemic area; expanding annular lesion | Annular erythema with central clearing; ≥5 cm; not scaly | Doxycycline 100 mg BID x 10-21 days; no serology needed if classic |
| Secondary syphilis | “Rash on palms and soles,” “not itchy” | Sexually active; palmar/plantar involvement; lymphadenopathy | Maculopapular rash including palms/soles; condyloma lata | RPR/VDRL; treat with penicillin; STI screening |
Workup#
Most acute rashes are diagnosed clinically—testing is rarely needed.
When to test:
| Test | When to order | Notes |
|---|---|---|
| KOH prep | Suspected tinea (annular, scaly border) | Scrape leading edge; look for hyphae |
| Viral swab (HSV/VZV PCR) | Vesicular rash; suspected zoster or HSV | Unroof vesicle; swab base |
| CBC with differential | Suspected DRESS, systemic illness | Eosinophilia in DRESS; leukocytosis in infection |
| LFTs, BMP, UA | Suspected DRESS or systemic drug reaction | Hepatitis, nephritis in DRESS |
| Skin biopsy | Uncertain diagnosis; suspected vasculitis; blistering disorder | Derm referral for biopsy usually |
| RPR/VDRL | Secondary syphilis in differential | Palmar/plantar involvement; sexually active |
When NOT to test:
- Classic viral exanthem with sick contacts
- Obvious contact dermatitis with clear exposure history
- Typical urticaria responding to antihistamines
- Classic pityriasis rosea with herald patch
Initial management#
- Identify and remove triggers: Stop suspect medications; avoid contactants
- Symptomatic relief: Antihistamines for pruritus; cool compresses
- Topical steroids: For inflammatory conditions (not infections)
- Assess for danger signs: Mucosal involvement, blistering, systemic symptoms
Management by diagnosis#
Contact dermatitis (allergic or irritant)#
Education:
- Allergic: immune reaction to specific substance (poison ivy, nickel, fragrances)
- Irritant: direct skin damage from harsh substances (soaps, solvents)
- Resolves in 2-3 weeks once exposure stops
- May take 24-72 hours for allergic contact to appear after exposure
Treatment:
| Drug | Dose | Contraindications | Monitoring | Cost | Notes |
|---|---|---|---|---|---|
| Triamcinolone 0.1% cream | Apply BID to affected areas x 2 weeks | Facial use >2 weeks; skin atrophy | Skin thinning with prolonged use | $ | Mid-potency; good for body |
| Hydrocortisone 2.5% cream | Apply BID x 2 weeks | None significant | None | $ | Low-potency; safe for face, intertriginous areas |
| Prednisone (severe/extensive) | 40-60 mg daily x 5-7 days, then taper over 2 weeks | Diabetes (monitor glucose); active infection | Blood glucose if diabetic | $ | For severe poison ivy or extensive involvement; short taper causes rebound |
| Cetirizine | 10 mg daily | None significant | None | $ | For pruritus; less sedating |
| Diphenhydramine | 25-50 mg Q6H PRN | Elderly (anticholinergic); urinary retention | Sedation | $ | More sedating; good for nighttime |
Follow-up: 2 weeks if not improving; consider patch testing referral for recurrent allergic contact dermatitis.
Drug eruption (morbilliform/exanthematous)#
Education:
- Most common drug reaction; usually 7-14 days after starting medication
- Common culprits: antibiotics (penicillins, sulfonamides, cephalosporins), anticonvulsants, allopurinol, NSAIDs
- Usually self-limited; resolves 1-2 weeks after stopping drug
- Does NOT always mean true allergy—may be able to use drug again (discuss with allergist)
Treatment:
- Stop the suspected drug (if possible and safe)
- Symptomatic treatment with antihistamines and topical steroids
- If drug is essential and reaction mild, may continue with close monitoring (shared decision)
| Drug | Dose | Contraindications | Monitoring | Cost | Notes |
|---|---|---|---|---|---|
| Cetirizine | 10 mg daily or BID | None significant | None | $ | First-line for pruritus |
| Hydroxyzine | 25 mg Q6H PRN | Elderly; QT prolongation | Sedation | $ | More sedating; good for severe itch |
| Triamcinolone 0.1% cream | Apply BID to affected areas | Widespread use | None | $ | Symptomatic relief |
Follow-up: 1-2 weeks; if not resolving or worsening, reassess diagnosis (consider DRESS, SJS).
When to worry (escalate to DRESS/SJS workup):
- Facial edema
- Mucosal involvement
- Fever persisting after drug stopped
- Lymphadenopathy
- Lab abnormalities (eosinophilia, elevated LFTs)
Viral exanthem#
Education:
- Common in children but occurs in adults
- Usually follows viral prodrome (fever, URI symptoms)
- Self-limited; resolves in 1-2 weeks
- Contagious during prodrome; less so once rash appears
Treatment:
- Supportive care only
- Antihistamines if pruritic
- Antipyretics for fever
Follow-up: No routine follow-up needed; return if not resolving in 2 weeks or new concerning symptoms.
Acute urticaria#
Education:
- Wheals (hives) caused by mast cell degranulation
- Individual lesions last <24 hours (if >24 hours, consider urticarial vasculitis)
- Common triggers: foods, medications, infections, insect stings
- Often no trigger identified
- Acute = <6 weeks; chronic = >6 weeks
Treatment:
| Drug | Dose | Contraindications | Monitoring | Cost | Notes |
|---|---|---|---|---|---|
| Cetirizine | 10 mg daily (can increase to 10 mg BID) | None significant | None | $ | First-line; can double dose if needed |
| Loratadine | 10 mg daily | None significant | None | $ | Alternative first-line; less sedating |
| Fexofenadine | 180 mg daily | None significant | None | $ | Alternative; least sedating |
| Diphenhydramine | 25-50 mg Q6H PRN | Elderly; urinary retention | Sedation | $ | Add for breakthrough or nighttime |
| Prednisone (severe) | 40-50 mg daily x 3-5 days | Diabetes; active infection | Blood glucose | $ | For severe/refractory; short course only |
| Epinephrine auto-injector | 0.3 mg IM PRN | None | None | $$ | Prescribe if any history of anaphylaxis or angioedema |
Follow-up: 1-2 weeks if not resolving; if persists >6 weeks, becomes chronic urticaria (different workup).
Pityriasis rosea#
Education:
- Likely viral etiology (HHV-6, HHV-7)
- Herald patch appears first, then generalized eruption 1-2 weeks later
- “Christmas tree” distribution on back
- Self-limited; resolves in 6-8 weeks
- Not contagious
Treatment:
- Reassurance—no treatment needed
- Antihistamines and emollients for pruritus
- UVB phototherapy if severe (derm referral)
| Drug | Dose | Contraindications | Monitoring | Cost | Notes |
|---|---|---|---|---|---|
| Cetirizine | 10 mg daily | None | None | $ | For pruritus |
| Triamcinolone 0.1% cream | Apply BID PRN | None | None | $ | For localized itchy areas |
Follow-up: No routine follow-up; return if not resolving by 8-10 weeks or atypical features.
Herpes zoster (shingles)#
Education:
- Reactivation of varicella-zoster virus in dorsal root ganglion
- Dermatomal distribution; does not cross midline
- Contagious to those who haven’t had chickenpox or vaccine (causes chickenpox, not shingles)
- Postherpetic neuralgia risk increases with age
- Vaccine recommended for adults ≥50 (Shingrix)
Treatment:
- Start antivirals within 72 hours of rash onset (or within 72 hours of new lesions appearing)
- Pain management critical to prevent PHN
| Drug | Dose | Contraindications | Monitoring | Cost | Notes |
|---|---|---|---|---|---|
| Valacyclovir | 1000 mg TID x 7 days | Renal impairment (adjust dose) | Cr if CKD | $ | First-line; better bioavailability than acyclovir |
| Acyclovir | 800 mg 5x daily x 7 days | Renal impairment (adjust dose) | Cr if CKD | $ | Alternative; more frequent dosing |
| Famciclovir | 500 mg TID x 7 days | Renal impairment (adjust dose) | Cr if CKD | $ | Alternative |
| Gabapentin | 100-300 mg TID, titrate to effect | Renal impairment | Sedation; dizziness | $ | For acute pain and PHN prevention |
| Prednisone | 60 mg daily x 7 days, taper over 2 weeks | Diabetes; immunocompromised | Blood glucose | $ | May reduce acute pain; does NOT prevent PHN; controversial |
Renal dosing:
- CrCl 30-49: Valacyclovir 1000 mg BID
- CrCl 10-29: Valacyclovir 1000 mg daily
- CrCl <10: Valacyclovir 500 mg daily
Ophthalmologic zoster (V1 distribution):
- Hutchinson sign (vesicles on nose tip) = high risk of ocular involvement
- Urgent ophthalmology referral same day
Follow-up: 1-2 weeks to assess healing and pain; if PHN develops, may need ongoing pain management.
Tinea corporis (ringworm)#
Education:
- Fungal infection of skin; contagious
- Spread by direct contact or fomites (towels, clothing)
- Can be acquired from pets (especially cats, dogs)
- Responds well to topical antifungals
Treatment:
| Drug | Dose | Contraindications | Monitoring | Cost | Notes |
|---|---|---|---|---|---|
| Terbinafine 1% cream | Apply daily x 1-2 weeks | None | None | $ | First-line; fungicidal; shorter course |
| Clotrimazole 1% cream | Apply BID x 2-4 weeks | None | None | $ | Alternative; longer course needed |
| Ketoconazole 2% cream | Apply daily x 2-4 weeks | None | None | $ | Alternative |
| Terbinafine (oral) | 250 mg daily x 2-4 weeks | Liver disease; drug interactions | LFTs if >2 weeks | $ | For extensive or refractory cases |
Follow-up: 2-4 weeks if not improving; consider oral therapy or derm referral if refractory.
Scabies#
Education:
- Caused by Sarcoptes scabiei mite burrowing into skin
- Highly contagious; spread by prolonged skin-to-skin contact
- Incubation 2-6 weeks for first infection; symptoms start within days for re-infestation
- Itching may persist 2-4 weeks after successful treatment (post-scabetic itch)
- All household members and close contacts must be treated simultaneously
Treatment:
| Drug | Dose | Contraindications | Monitoring | Cost | Notes |
|---|---|---|---|---|---|
| Permethrin 5% cream | Apply neck-down, wash off after 8-14 hours; repeat in 1 week | None significant | None | $ | First-line; apply to ALL skin from neck down including under nails |
| Ivermectin (oral) | 200 mcg/kg x 1 dose; repeat in 1-2 weeks | Pregnancy; weight <15 kg | None | $ | Alternative; easier compliance; use for crusted scabies or treatment failure |
| Hydroxyzine | 25 mg Q6H PRN | Elderly; QT prolongation | Sedation | $ | For pruritus; itch persists weeks after treatment |
Environmental measures:
- Wash all bedding, clothing, towels in hot water and dry on high heat
- Items that can’t be washed: seal in plastic bag for 72 hours
- Vacuum furniture and carpets
Follow-up: 2-4 weeks; if still symptomatic, reassess for treatment failure vs post-scabetic itch vs reinfestation.
Erythema migrans (Lyme disease)#
Education:
- Caused by Borrelia burgdorferi transmitted by Ixodes tick
- Classic rash: expanding annular erythema ≥5 cm, often with central clearing (“bull’s eye”)
- Rash appears 3-30 days after tick bite
- Early treatment prevents disseminated disease
- Endemic areas: Northeast, upper Midwest, Pacific coast
Treatment:
- Do NOT wait for serology—treat based on clinical diagnosis
- Serology often negative in early disease
| Drug | Dose | Contraindications | Monitoring | Cost | Notes |
|---|---|---|---|---|---|
| Doxycycline | 100 mg BID x 10-21 days | Pregnancy; children <8 years | None | $ | First-line; also covers other tick-borne infections |
| Amoxicillin | 500 mg TID x 14-21 days | Penicillin allergy | None | $ | Alternative for pregnancy, children |
| Cefuroxime | 500 mg BID x 14-21 days | Cephalosporin allergy | None | $ | Alternative |
Follow-up: 2-4 weeks; if symptoms persist or new symptoms develop (arthritis, facial palsy, heart block), reassess for disseminated Lyme.
Follow-up#
- Contact dermatitis: 2 weeks if not improving
- Drug eruption: 1-2 weeks; sooner if worsening
- Viral exanthem: No routine follow-up; return if not resolving in 2 weeks
- Urticaria: 1-2 weeks; if >6 weeks, chronic urticaria workup
- Pityriasis rosea: No routine follow-up; return if not resolving by 8-10 weeks
- Zoster: 1-2 weeks to assess healing and pain
- Tinea: 2-4 weeks if not improving
Return precautions (all patients):
- Rash spreading rapidly
- New blisters or skin peeling
- Mouth sores, eye redness, or genital sores
- Fever or feeling very unwell
- Difficulty breathing or swallowing
- Rash not improving after 2 weeks of treatment
Patient instructions#
- Avoid scratching—this can cause infection and scarring. Keep nails short.
- Apply cool compresses to itchy areas for relief.
- Use fragrance-free moisturizers and gentle soaps.
- If you have a new rash after starting a medication, call the office—do not stop the medication without talking to us first unless you have trouble breathing or swallowing.
- Take antihistamines as directed for itching. They may cause drowsiness.
- Apply prescription creams only to affected areas, not all over your body.
- Call the office or go to the ER if you develop mouth sores, eye problems, blisters, skin peeling, high fever, or difficulty breathing.
Smartphrase snippets#
.RASHCONTACT
Acute rash consistent with contact dermatitis. Distribution and history suggest [allergic/irritant] reaction to [exposure]. No mucosal involvement or systemic symptoms. Plan: avoid offending agent, triamcinolone 0.1% cream BID x 2 weeks, cetirizine 10 mg daily for pruritus. Discussed return precautions.
.RASHDRUG
Morbilliform drug eruption, likely secondary to [medication] started [timeframe] ago. No mucosal involvement, facial edema, or systemic symptoms to suggest DRESS or SJS. Plan: discontinue [medication], symptomatic treatment with antihistamines and topical steroids. Close follow-up in 1-2 weeks. Discussed warning signs requiring immediate evaluation.
.RASHZOSTER
Herpes zoster affecting [dermatome]. Rash onset [timeframe]. Started valacyclovir 1000 mg TID x 7 days within 72-hour window. Discussed pain management, contagiousness to non-immune individuals, and postherpetic neuralgia risk. [Ophthalmology referral arranged for V1 involvement.] Follow-up in 1-2 weeks.