One-liner#

Distinguish true bacterial cellulitis requiring antibiotics from inflammatory dermatitis requiring steroids—getting this wrong leads to treatment failure, unnecessary antibiotics, or worsening infection.

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#

• Rapidly spreading erythema (mark borders—if spreading >1 cm/hour)
• Systemic toxicity: fever >101°F, tachycardia, hypotension, altered mental status
• Crepitus or pain out of proportion to exam → necrotizing fasciitis
• Periorbital or orbital involvement
• Immunocompromised with any cellulitis
• Failed outpatient antibiotics with worsening
• Unable to tolerate oral antibiotics

Key history#

Onset and progression:

• Acute (<48-72 hours) favors cellulitis
• Gradual or chronic favors dermatitis
• Rapid spread with systemic symptoms = urgent

Symptoms:

• Pain: cellulitis is typically painful; dermatitis is typically itchy
• Fever/chills: suggests infection
• Pruritus: suggests dermatitis (though infected dermatitis can occur)

Predisposing factors for cellulitis:

• Portal of entry: cut, abrasion, insect bite, ulcer, tinea pedis, fissure
• Lymphedema, venous insufficiency
• Prior cellulitis (same location)
• Diabetes, immunocompromise
• IV drug use

Predisposing factors for dermatitis:

• History of eczema, stasis dermatitis, contact dermatitis
• New exposures (products, plants, occupational)
• Bilateral involvement (cellulitis is almost always unilateral)

Prior episodes:

• Recurrent in same location: consider underlying venous disease, lymphedema, or chronic dermatitis
• Prior response to antibiotics vs steroids

Focused exam#

Key distinguishing features:

Exam checklist:

• Vitals: fever, tachycardia
• Skin:
  • Unilateral vs bilateral
  • Borders: mark with pen to track progression
  • Surface changes: scale, vesicles, crust
  • Warmth compared to contralateral side
  • Tenderness
• Lymph nodes: regional lymphadenopathy
• Distal pulses: if lower extremity
• Between toes: tinea pedis (common portal of entry)

Differential (quick pattern recognition)#

Common/likely (outpatient)#

Can’t-miss / urgent#

Workup#

Most cases are diagnosed clinically. Labs and imaging rarely change management.

When to test:

When NOT to test:

• Uncomplicated cellulitis in healthy patient
• Obvious stasis dermatitis or contact dermatitis
• Mild insect bite reaction

Initial management#

The critical decision: antibiotics or steroids?

If uncertain:

• Err on side of antibiotics if any systemic symptoms
• Can add topical steroids if dermatitis component suspected
• Close follow-up in 48-72 hours to reassess
• Do NOT give steroids alone if infection possible

Management by diagnosis#

Cellulitis (non-purulent)#

Education:

• Bacterial skin infection, usually Streptococcus or Staphylococcus
• Needs antibiotics; will not resolve on its own
• Elevation helps reduce swelling
• May look worse before better in first 24-48 hours (inflammatory response)
• Mark borders to track progression

Treatment:

Renal dosing:

• Cephalexin: CrCl 10-50: 250-500 mg Q8-12H; CrCl <10: 250 mg Q12-24H
• Clindamycin: No adjustment needed

Duration: 5 days usually sufficient; extend to 7-10 days if slow response or immunocompromised

Follow-up: 48-72 hours to ensure improvement; if worsening, consider MRSA, abscess, or alternative diagnosis.

Recurrent cellulitis prophylaxis (≥3-4 episodes/year):

• Address predisposing factors: treat tinea pedis, manage lymphedema, compression for venous disease
• Prophylactic antibiotics:
  • Penicillin VK 250-500 mg BID, OR
  • Erythromycin 250 mg BID (if penicillin allergic)
  • Duration: typically 6-12 months; recurrence common after stopping

Cellulitis (purulent) or with abscess#

Education:

• Purulent cellulitis more likely MRSA
• Abscess requires drainage—antibiotics alone won’t work
• May need to pack wound and return for repacking

Treatment:

Abscess:

• Incision and drainage is primary treatment
• Antibiotics alone insufficient for abscess

Antibiotics for purulent cellulitis or cellulitis surrounding abscess:

If both strep and MRSA coverage needed: TMP-SMX + cephalexin, OR doxycycline alone, OR clindamycin alone

Follow-up: 48-72 hours; wound check if packed.

Stasis dermatitis (commonly misdiagnosed as cellulitis)#

Education:

• Inflammatory condition from chronic venous insufficiency—NOT infection
• Bilateral involvement is key distinguishing feature
• Antibiotics will not help and may cause harm (C. diff, resistance)
• Compression is the most important treatment
• Can become secondarily infected (then needs antibiotics)

Treatment:

Do NOT use:

• Antibiotics (unless signs of true infection: fever, unilateral worsening, purulence)
• Neomycin-containing products (high sensitization rate)
• High-potency steroids long-term

Signs of secondary infection in stasis dermatitis:

• Unilateral worsening
• Fever
• Increased pain (not just itch)
• Purulent drainage
• Rapid spread

Follow-up: 2-4 weeks; vascular surgery referral for severe venous disease.

Contact dermatitis (commonly misdiagnosed as cellulitis)#

Education:

• Inflammatory reaction to contactant—NOT infection
• Can be allergic (immune-mediated) or irritant (direct damage)
• Geometric or linear pattern suggests contact
• Antibiotics will not help

Treatment:

Follow-up: 2 weeks if not improving; patch testing referral for recurrent cases.

Erysipelas#

Education:

• Superficial cellulitis with sharply demarcated, raised borders
• Usually caused by Streptococcus
• Common on face and lower legs
• Responds well to antibiotics targeting strep

Treatment:

Follow-up: 48-72 hours; if recurrent, consider prophylactic antibiotics and address predisposing factors (tinea pedis, lymphedema).

Abscess#

Education:

• Collection of pus that requires drainage
• Antibiotics alone will not cure an abscess
• May need packing and wound care
• Often caused by MRSA

Treatment:

• Incision and drainage is definitive treatment
• Pack wound if cavity present
• Antibiotics indicated if:
  • Surrounding cellulitis
  • Systemic symptoms
  • Immunocompromised
  • Multiple abscesses
  • Abscess on face or hand

Follow-up: 48-72 hours for wound check and possible repacking.

Follow-up#

• Cellulitis: 48-72 hours to ensure improvement; if worsening, reassess
• Stasis dermatitis: 2-4 weeks
• Contact dermatitis: 2 weeks if not improving
• Abscess: 48-72 hours for wound check

Return precautions:

• Redness spreading beyond marked borders
• Fever or feeling very unwell
• Increased pain
• Red streaks going up the limb
• Pus or drainage
• Not improving after 48-72 hours of antibiotics

Patient instructions#

For cellulitis:

• Take all antibiotics exactly as prescribed, even if you feel better.
• Elevate the affected area above your heart as much as possible.
• We marked the borders of the redness—watch to make sure it doesn’t spread beyond the marks.
• It’s normal for the area to look slightly worse in the first 24-48 hours before it gets better.
• Call the office or go to the ER if the redness spreads, you develop fever, or you feel very sick.

For dermatitis:

• This is inflammation, not infection—antibiotics won’t help.
• Apply the steroid cream only to the affected areas.
• Moisturize frequently with fragrance-free products.
• Avoid the trigger that caused this reaction.
• If you have leg swelling, wear compression stockings and elevate your legs.

Smartphrase snippets#

.CELLULITIS Cellulitis of [location]. Unilateral erythema, warmth, and tenderness with [portal of entry identified/no clear portal]. No abscess on exam. No systemic toxicity. Marked borders with pen. Plan: [antibiotic] x [duration], elevation, close follow-up in 48-72 hours. Discussed return precautions including spreading redness, fever, or worsening symptoms.

.STASISNOTCELLULITIS Bilateral lower extremity erythema consistent with stasis dermatitis, NOT cellulitis. Key features: bilateral involvement, chronic venous changes (varicosities, hemosiderin staining), pruritus rather than pain, no fever. Antibiotics not indicated. Plan: compression stockings, leg elevation, triamcinolone 0.1% ointment BID, emollients. Discussed that this is inflammation from vein problems, not infection.

.ABSCESSID Abscess of [location], [size]. Incision and drainage performed. [Packing placed / No packing needed]. Wound care instructions provided. [Antibiotics prescribed for surrounding cellulitis / No antibiotics needed as no surrounding cellulitis]. Follow-up in 48-72 hours for wound check [and repacking].