Intact skin blocks microbes through a tough outer layer, an acidic surface, and normal flora. Infection follows a break in the barrier (scratching, wounds, burns, maceration) or reduced host defense (diabetes, immunosuppression, older age, poor circulation).

Contagious periods

• Varicella: from 1–2 days before the rash until all lesions have crusted
• Impetigo: until lesions are crusted/dry or 24 hours after starting effective antibiotics
• Herpes zoster: fluid in open vesicles can transmit varicella (not shingles) to non-immune people

• Lesion type, distribution, color, drainage, odor, size; mark the border of cellulitis with a skin marker and time
• Pain, itching, warmth, swelling, lymphangitic streaks
• Systemic signs: fever, tachycardia, hypotension (sepsis)
• Zoster: prodromal burning or tingling pain before the rash; check for eye involvement (vesicles on the tip of the nose — Hutchinson sign)
• Scabies: itching of household members
• Risk factors: diabetes, immunosuppression, contact sports, crowded living, pets (tinea from cats and dogs)

Bacterial

• Impetigo (limited): topical mupirocin or retapamulin; extensive: oral cephalexin or dicloxacillin (clindamycin, doxycycline, or TMP-SMX if MRSA)
• Non-purulent cellulitis: beta-lactam active against streptococci (cephalexin; IV cefazolin if severe)
• Purulent infection / abscess: incision and drainage is the key treatment; add MRSA-active antibiotics (TMP-SMX, doxycycline, clindamycin; IV vancomycin if severe)
• Necrotizing infection: emergency surgical debridement, broad-spectrum IV antibiotics, including clindamycin to suppress toxin production
• Diabetic foot infection: debridement, offloading, antibiotics guided by severity and culture

Viral

• Herpes zoster: start oral antivirals within 72 hours of rash onset (valacyclovir, famciclovir, or acyclovir) to shorten illness and reduce complications; pain control (acetaminophen, NSAIDs, gabapentinoids, opioids if needed)
• Postherpetic neuralgia: gabapentin, pregabalin, topical lidocaine, tricyclics
• Genital warts: patient-applied imiquimod or podofilox, or clinician cryotherapy, trichloroacetic acid, surgery

Fungal

• Tinea corporis/pedis: topical azoles or terbinafine
• Tinea capitis requires oral therapy (griseofulvin or terbinafine) for weeks; topical agents alone do not reach the hair follicle
• Candidiasis: topical azoles or nystatin; keep folds dry

Parasitic

• Scabies: permethrin 5% cream applied from the neck down (include scalp and face in infants and older adults), left on 8–14 hours, repeated in 1–2 weeks; oral ivermectin as an alternative; treat all close contacts at the same time
• Lice: permethrin 1% or another pediculicide, nit combing, repeat treatment per product directions

Varicella post-exposure prophylaxis

• Non-immune exposed contacts: varicella vaccine within 3–5 days
• VariZIG up to 10 days after exposure for high-risk people (pregnant, immunocompromised, certain newborns)
• Exposed non-immune staff are off duty from day 8 after the first exposure through day 21 after the last exposure (through day 28 if they received VariZIG)

Drug safety

Listed in priority order.

1. Recognize sepsis and necrotizing infection — rapid spread, severe pain, hypotension, crepitus → escalate immediately
2. Infection control
   • Contact precautions for draining wounds, MRSA, impetigo in the hospital, scabies
   • Varicella and disseminated zoster (or zoster in an immunocompromised client): airborne and contact precautions; localized zoster in an immunocompetent client: standard precautions with lesions covered. Only immune staff should care for these clients
   • Hand hygiene; dedicated equipment
3. Assess response to treatment — the best early sign that cellulitis is responding is that the marked border stops spreading; also falling fever and pain. Redness may look worse in the first 24–48 hours before improving
4. Local care
   • Elevate an affected limb
   • Impetigo: gently soak and remove crusts, then apply ointment
   • Keep nails short; mittens or gloves for young children to prevent scratching and autoinoculation
   • Zoster: keep lesions clean and dry, loose clothing, cool compresses for comfort; avoid rubbing or scratching
5. Pain management — especially zoster; reassess regularly
6. Screen and treat contacts — household members for tinea capitis, scabies, and impetigo; sexual partners for genital warts

• Hand hygiene; do not share towels, razors, combs, hats, or sports equipment
• Tinea capitis: family members should be checked and treated if infected; wash or discard combs and brushes; take the full oral course
• After contact with an animal or person with ringworm, wash the area promptly with soap and water; take pets with patchy hair loss to a veterinarian
• Keep feet dry, change socks daily, wear sandals in public showers
• Varicella: stay home from school or work until all lesions have crusted
• Shingles vaccine: two doses of recombinant zoster vaccine, 2–6 months apart, for adults 50 and older and adults 19 and older who are immunocompromised. RZV is non-live and can be given regardless of prior chickenpox, shingles, or live zoster vaccine; the live varicella vaccine is contraindicated in pregnancy and immunosuppression
• Shingles: avoid contact with pregnant people, newborns, and immunocompromised people who have not had chickenpox until lesions crust
• Genital warts: spread by sexual contact; partners should be examined; condoms reduce but do not eliminate risk; HPV vaccination prevents most genital warts and HPV cancers
• Scabies: apply cream to the entire body as directed; wash bedding and clothes in hot water or seal in a bag for at least 72 hours; itching may last weeks
• Complete antibiotic courses; report spreading redness, fever, or new pain

• Impetigo: honey-colored crusts; contagious; short nails and mittens prevent spread
• Cellulitis: mark the border; stopping spread is the key sign of response; elevate
• Abscess: incision and drainage first; MRSA coverage if purulent
• Pain out of proportion = necrotizing fasciitis — emergency surgery
• Zoster: unilateral dermatomal painful vesicles; antivirals within 72 hours; don't scratch
• Varicella: contagious until all lesions crusted; airborne + contact precautions
• Recombinant zoster vaccine: 2 doses, age 50+, or 19+ if immunocompromised
• Tinea capitis needs oral therapy; examine the family; Wood's lamp green in Microsporum
• Genital warts (HPV): partners examined, HPV vaccine
• Scabies: permethrin neck down, repeat in 1–2 weeks, treat all contacts together
• Burn wound green exudate → Pseudomonas
• Vancomycin: slow infusion, kidney function and levels