Impetigo

Impetigo is a common, highly contagious bacterial skin infection that mainly affects infants and young children, though anyone can get it. It causes red sores that quickly rupture, ooze, and form a characteristic honey-colored crust. The infection is usually caused by Staphylococcus aureus or group A Streptococcus.

Impetigo spreads easily through close contact and shared items. It is generally mild and responds well to topical or oral antibiotics. Prompt treatment reduces spread to others and to other parts of the body. Good hygiene helps prevent recurrence and transmission.

There are two main forms:

Nonbullous impetigo (most common)

• Red sores that rupture quickly
• Honey-colored crusts, often around the nose and mouth, but can occur on arms, legs, or other exposed areas
• Mild itching or soreness
• Satellite lesions from scratching and autoinoculation

Bullous impetigo

• Larger fluid-filled blisters that stay intact longer
• Clear or cloudy fluid; surrounding skin may be red
• More common in infants and young children; often in intertriginous areas

Ecthyma is a deeper form that causes painful ulcers with a hard crust, more often on the legs, and may scar.

Fever is uncommon in simple impetigo; significant systemic symptoms suggest a more serious infection.

Impetigo is caused by bacteria — primarily Staphylococcus aureus (including MRSA in some communities) and Streptococcus pyogenes (group A strep). Bacteria enter through minor skin breaks: cuts, insect bites, scratches, or areas of eczema or other dermatitis. The infection is contagious until crusts heal or until at least 24 hours of effective antibiotic treatment. Close contact sports, crowded living conditions, and warm humid weather facilitate spread.

Risk factors include:

• Age 2–5 years (peak incidence)
• Close contact with an infected person (household, daycare, school, sports)
• Existing skin conditions that break the barrier (eczema, scabies, insect bites, cuts)
• Warm, humid climates
• Crowded living situations
• Participation in contact sports
• Weakened immune system

Complications are uncommon with timely treatment but can include:

• Cellulitis or deeper soft-tissue infection
• Lymphangitis
• Post-streptococcal glomerulonephritis (after strep impetigo — not prevented by antibiotics as reliably as rheumatic fever is)
• Scarring (more likely with ecthyma)
• MRSA-related treatment challenges
• Rarely, invasive strep or staph disease
• Outbreaks in families or institutions

To reduce spread and recurrence:

• Wash hands frequently with soap and water
• Keep cuts, scrapes, and insect bites clean and covered
• Avoid sharing towels, clothing, razors, and sports equipment
• Wash infected person’s clothes, towels, and bedding daily during treatment
• Trim nails to discourage scratching
• Treat underlying eczema or other skin conditions
• Keep children home from school or daycare until at least 24 hours of antibiotics and improving lesions, per local guidance

Diagnosis is usually clinical based on the appearance of honey-colored crusts or characteristic blisters. Swab culture of exudate or crusted lesions can identify the organism and guide therapy when MRSA is a concern, when treatment fails, or in outbreak settings. Differential diagnosis includes cold sores (HSV), chickenpox, contact dermatitis, tinea, and eczema flares.

See a clinician for suspected impetigo so appropriate antibiotics can be started and other conditions excluded. Seek care sooner if sores are widespread, the person is a newborn or immunocompromised, there is fever or increasing pain/swelling, or the rash is not improving after a few days of treatment. Return promptly if red streaks, swelling of lymph nodes, or systemic illness develops.

Treatment depends on extent and severity:

• Limited disease — topical antibiotics such as mupirocin or retapamulin applied to lesions and often to the nostrils if staph carriage is suspected; continue for the prescribed duration (commonly 5 days)
• More extensive disease, multiple sites, outbreaks, or systemic features — oral antibiotics active against staph and strep (cephalexin, dicloxacillin, or alternatives; clindamycin, trimethoprim-sulfamethoxazole, or others when MRSA is likely)
• Gentle cleansing of crusts with warm water or saline to improve topical medication contact
• Avoid scratching; use bandages on exposed areas if needed to reduce spread
• Evaluate household contacts for secondary cases

Improvement is usually visible within a few days. Complete the full course of antibiotics.

At home:

• Apply prescribed topical antibiotic as directed after gentle cleaning
• Wash hands before and after touching lesions
• Use separate towels and wash bedding frequently
• Keep nails short
• Cover sores loosely if they are in areas likely to be touched or to contact others
• Do not share sports gear or personal items
• Return for care if new lesions continue to appear after 48–72 hours of treatment or if fever develops

Bring:

• When sores started and how they have spread
• Photos if lesions have changed
• History of eczema, recent cuts, or family members with similar sores
• Antibiotic allergies
• Questions about return to school/sports and preventing household spread