impetigo

Overview
Impetigo is a highly contagious bacterial skin infection that primarily affects infants and young children, though anyone can get it. It’s caused by Staphylococcus aureus or Streptococcus pyogenes, two common bacteria that live harmlessly on the skin or in the nose until they enter through a break in the skin. Once inside, they multiply rapidly and cause small red sores or blisters that rupture and form the characteristic honey-colored crust. Though impetigo is generally mild and superficial, it can spread quickly through direct contact or contaminated items such as towels, toys, or bedding.

Why It’s Important
While not life-threatening, impetigo can cause significant discomfort, itching, and embarrassment, especially in children. Because it spreads easily in settings like schools, daycare centers, and households, even a single case can lead to small outbreaks. Early identification and treatment help prevent spread, reduce symptoms, and avoid rare but serious complications such as cellulitis or post-streptococcal glomerulonephritis, a kidney disorder that can follow certain bacterial infections. Prompt care also helps prevent scarring or secondary infections from scratching.

Quick Facts

  • Common age group: Children ages 2–5 years

  • Caused by: Staphylococcus aureus or Streptococcus pyogenes

  • Transmission: Direct skin contact or via contaminated objects

  • Forms:

    • Non-bullous impetigo (most common) – small red sores, honey-colored crust

    • Bullous impetigo – large fluid-filled blisters caused by S. aureus toxin

    • Ecthyma – deeper, ulcerative form affecting lower skin layers

  • Duration: Typically lasts 7–10 days with treatment

  • Contagious: Highly – until lesions are crusted over or 24–48 hours after antibiotics begin

What Happens in the Body
When the skin barrier is broken by cuts, insect bites, eczema, or other irritations, bacteria invade the outermost layer (epidermis). The body’s immune response causes inflammation and fluid accumulation, forming blisters or pustules filled with bacteria. As these rupture, they ooze and form crusts that can spread bacteria to other areas of skin or to other people. In bullous impetigo, bacterial toxins break down cell connections, leading to large, fragile blisters that easily burst.

Common Signs and Symptoms

  • Red sores or blisters, usually on the face, nose, mouth, arms, or legs

  • Sores that burst and form golden or honey-colored crusts

  • Mild pain or itching; sometimes burning sensation

  • Swollen lymph nodes near affected areas

  • Larger blisters (bullae) filled with clear or cloudy fluid in bullous impetigo

  • Mild fever in more widespread infections

Diagnosis

  • Clinical examination: Most cases are diagnosed based on the appearance of sores

  • Bacterial culture: A swab from a lesion can confirm the type of bacteria, especially if the infection is recurrent, severe, or unresponsive to treatment

  • Differential diagnosis: Must be distinguished from herpes simplex, eczema, or contact dermatitis

Treatment and Management

  • Topical antibiotics:

    • Mupirocin or retapamulin for mild, localized infections

  • Oral antibiotics:

    • Dicloxacillin or cephalexin for more widespread cases or in outbreaks

    • Alternatives like clindamycin may be used if MRSA is suspected

  • Hygiene measures:

    • Gently wash affected areas with mild soap and water

    • Keep nails short to prevent scratching and secondary infection

    • Avoid sharing towels, clothing, or bedding

  • Return to school or daycare: Only after 24 hours of antibiotic therapy or once sores are dry and crusted

  • Home care: Cover lesions lightly to minimize spreading and maintain cleanliness

Risks and Complications

  • Cellulitis – a deeper skin infection that can spread quickly

  • Post-streptococcal glomerulonephritis – inflammation of the kidneys following Strep infection (rare)

  • Scarring – uncommon, but may occur if lesions become ulcerated or secondarily infected

  • Reinfection – common in children with eczema or nasal S. aureus colonization

Who Is at Risk

  • Young children, especially in group settings

  • Individuals with eczema, insect bites, or open wounds

  • Warm, humid climates, which favor bacterial growth

  • Athletes in close-contact sports (e.g., wrestling)

  • People with weakened immune systems or poor hygiene access

Related Conditions

  • Eczema (can increase susceptibility)

  • Cellulitis

  • Scabies (can mimic early impetigo)

  • Folliculitis (hair follicle infections caused by similar bacteria)

When to See a Doctor
Seek medical attention if:

  • Sores are spreading quickly or not improving after 3 days of treatment

  • There is pain, fever, or swelling around lesions

  • The infection recurs frequently or appears severe (bullous form)

  • The affected person is an infant or immunocompromised

Last Updated: October 4, 2025