Lead
A scratch from a bug bite turned into a blister overnight. Two days later, the same lesion had appeared on the face. The name "impetigo" — sometimes translated from Japanese as "tobi-hi," meaning it "flies" from one spot to another — fits the course well. It is a common bacterial skin infection in summer, and particularly common in children.
The reason infection "flies" is straightforward: the fluid from lesions, and the broken-open blisters, spread bacteria on contact with skin. How antibiotics are used and what happens at home directly shapes how fast the infection resolves.
Two Types of Impetigo
Impetigo — technically called impetigo contagiosa — comes in two main forms.
Bullous impetigo (approximately 70% of cases): Staphylococcus aureus produces an exotoxin: a toxin secreted by bacteria into surrounding tissue, where it damages cells or disrupts normal function (exfoliative toxin: bacterial toxin that cleaves the protein holding skin layers together, causing the outer layer to peel off) that disrupts adhesion between epidermal cells, creating clear-to-yellow fluid-filled blisters. Itching is intense; when the blisters rupture, bacteria spread to adjacent skin. Fever is mild or absent [1,2].
Non-bullous (crusted) impetigo (the remaining ~30%): caused by group A <em>Streptococcus</em>: bacterium responsible for strep throat and, when undertreated, rheumatic fever; the most common cause of crusted impetigo, or a mixed infection with S. aureus. After blisters rupture, honey-colored crusts form. Inflammation is more pronounced, and fever and lymph node swelling may accompany it [1,2].
The two types have slightly different treatment priorities. In the crusted form, the involvement of streptococcus makes completing a full course of antibiotics important — inadequate treatment carries a risk of rheumatic fever.
Antibiotic Choice and Duration
The first-line antibiotic for impetigo is a first-generation cephalosporin such as cefalexin. A 7–10-day course achieves cure in approximately 90% of cases [1]. Topical antibiotics (mupirocin and similar agents) are effective for localized disease, but oral antibiotics are needed when lesions are widespread or systemic symptoms are present.
A growing concern is community-acquired MRSA: methicillin-resistant <em>Staphylococcus aureus</em>, a strain resistant to most standard antibiotics and harder to treat (methicillin-resistant S. aureus). In Japan, as elsewhere, there is regional variation, but cases where standard cephalosporins prove ineffective are increasing [5]. If you feel a usual course of antibiotics is not working as expected, asking the physician about culture and sensitivity testing is a reasonable step.
Complete the full prescribed course even when symptoms improve. This is especially true for the crusted form involving streptococcus, where incomplete treatment is associated with rheumatic fever risk.
Preventing Spread Within the Household
Impetigo spreads primarily through direct contact with lesions and through shared objects — towels, clothing. Practical steps for limiting household spread:
Keep fingernails short. Scratching the lesions and then touching other skin is a primary route of spread. Short nails and discouraging scratching matter.
Do not share towels or clothing. Towels and clothing that have touched the affected area should ideally be washed separately from other family members' items.
Cover the lesions. A gauze dressing or bandage over the affected area reduces direct-contact transmission.
For daycare and school attendance, policies vary by facility — some say "covered lesions are fine"; others specify a number of days after starting antibiotics. Checking your facility's rules in advance avoids a scramble when the situation arises.
When to Seek Care Promptly
The following are signs that warrant an early visit to a clinician:
- Lesions spreading rapidly
- Fever above 38°C (100.4°F) or significant malaise
- No improvement with topical treatment after three days
- Lesions on or near the face or around the eyes
In infants, extensive impetigo can occasionally progress to staphylococcal scalded skin syndrome: severe skin peeling triggered by staph exotoxins circulating in the bloodstream, resembling a burn; most common and dangerous in infants (SSSS), a generalized condition in which the skin reddens and peels across the body. If this develops, seek medical attention without delay.
Summary
Most cases of impetigo resolve quickly with appropriate antibiotics and household infection control. Understanding the two types, completing the prescribed course, and preventing secondary spread within the family are the three pillars of management. Keeping a dated record of lesion extent and progression is practically useful when communicating with a clinician — "is it spreading or contracting" is hard to convey verbally but easy to show.
References
- Hartman-Adams H, Banvard C, Juckett G. Impetigo: diagnosis and treatment. Am Fam Physician. 2014;90(4):229–235. PMID: 25250997.
- Nardi NM, Schaefer TJ. Impetigo. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023. PMID: 32119383.
- Bowen AC, Tong SYC, Andrews RM, et al. Short-course oral co-trimoxazole versus intramuscular benzathine benzylpenicillin for impetigo in a highly endemic region: an open-label, randomised, controlled, non-inferiority trial. Lancet. 2014;384(9960):2132–2140. doi:10.1016/S0140-6736(14)60744-3. PMID: 25172578.
- Moran GJ, Krishnadasan A, Gorwitz RJ, et al. Methicillin-resistant S. aureus infections among patients in the emergency department. N Engl J Med. 2006;355(7):666–674. doi:10.1056/NEJMoa055356. PMID: 16914702.
- Japanese Dermatological Association. Guidelines for Management of Skin Infections 2009. J Dermatol. 2009;119(6):1133–1193.