Impetigo is described on physical exam by identifying its characteristic morphology, which differs depending on whether you are looking at the non-bullous or bullous form. Non-bullous impetigo produces the classic honey-colored crusts on an erythematous base, while bullous impetigo shows flaccid, thin-roofed blisters that rupture into shallow erosions rimmed by a collarette of scale. Getting the description right matters for documentation, differential diagnosis, and communicating findings clearly to colleagues, so understanding the specific vocabulary and features for each form is worth the effort.
Non-Bullous Impetigo and the Honey-Colored Crust
Non-bullous impetigo is by far the more common form, and its description follows a predictable morphologic sequence. The lesion begins as a single red macule, a flat area of erythema with no elevation. That macule then evolves into a small vesicle or pustule, which is the brief, fluid-filled stage. The vesicle or pustule ruptures, releasing serous contents that dry on the skin surface. What remains is the hallmark finding: a thick, adherent, honey-colored crust sitting on a shallow erosion.1DermNet. Impetigo
When documenting this on exam, the key descriptors are the crust color and texture. The crust is classically described as “honey-colored” or “golden,” though in practice it can also appear yellowish-brown. It tends to be irregularly shaped, sometimes with satellite lesions nearby from autoinoculation, where the patient has scratched and spread the infection to adjacent skin. You might note that surrounding erythema is minimal or absent, which is a useful detail because many other crusted conditions show more prominent inflammation around the lesion.1DermNet. Impetigo
A well-written exam note for non-bullous impetigo might read something like: “Several grouped, honey-colored crusted lesions with underlying shallow erosions on an erythematous base, with minimal surrounding erythema, located on the perioral region.” That single sentence captures the morphology (crusts on erosions), the color (honey-colored), the arrangement (grouped), and the location. Each of those elements gives the reader of your note a clear mental picture.
Bullous Impetigo and Its Distinct Morphology
Bullous impetigo looks quite different and calls for a different set of descriptors. Rather than crusts, the primary lesion is a bulla, a fluid-filled blister larger than the typical vesicle. These bullae start as small vesicles that rapidly enlarge into flaccid, superficial blisters that can reach up to about two centimeters in diameter. The fluid inside is initially clear but often becomes cloudy or frankly purulent over time.2PubMed Central. Pediatric Bullous Impetigo: A Case Report and Literature Review
Because the roof of the bulla is extremely thin and fragile, intact bullae are sometimes hard to catch on exam. The blisters rupture easily, and what you find instead is the ruptured stage: a shallow, moist, red erosion bordered by a ring of residual scale from the collapsed blister wall. This rim is called a collarette of scale, and documenting it is one of the most useful morphologic clues because it tells you a bulla was there even though you are seeing it after it burst.2PubMed Central. Pediatric Bullous Impetigo: A Case Report and Literature Review A thin brown crust may also overlie the erosion, but it is typically much thinner and less adherent than the thick golden crust of non-bullous impetigo.
Documentation for bullous impetigo might read: “Well-demarcated cluster of flaccid bullae with clear-to-turbid fluid, several ruptured with annular erosions and collarettes of scale, on the trunk and intertriginous folds, without surrounding erythema or edema.” Notice how the description names the primary lesion (flaccid bullae), their contents (clear-to-turbid fluid), the secondary changes (annular erosions and collarettes), and the distribution. It also notes the absence of surrounding erythema, which is a commonly reported feature of bullous impetigo lesions.3PubMed Central. Staphylococcal Scalded Skin Syndrome and Bullous Impetigo
Where Impetigo Shows Up on the Body
Distribution is a core part of any skin exam description, and impetigo has fairly predictable patterns depending on the subtype. Non-bullous impetigo has a strong predilection for the face, especially the perioral region and around the nose. In children, the face is one of the most frequently involved areas, with lesions often starting near the mouth and then spreading to other body regions through touching and scratching.4PubMed. Facial and perioral primary impetigo: a clinical study You will also see it on the extremities, particularly where there are breaks in the skin from insect bites, abrasions, or eczema.
Bullous impetigo, on the other hand, tends to show up on the trunk, extremities, and intertriginous areas such as the axillae, neck folds, and diaper region in infants.3PubMed Central. Staphylococcal Scalded Skin Syndrome and Bullous Impetigo The intertriginous involvement is worth specifying on your exam because it can help distinguish bullous impetigo from other blistering conditions that favor different sites. In a diaper-wearing infant, for instance, noting bullae in the diaper area and skin folds is a meaningful distributional clue.
When you document distribution, be as specific as possible. “Scattered across the body” is far less helpful than “clustered perioral lesions extending to the bilateral cheeks, with a few satellite lesions on the right forearm.” Mentioning whether lesions are unilateral or bilateral, clustered or diffuse, and whether they spare or favor certain areas gives the next clinician real information to work with.
Describing the Stage of the Lesion
One challenge in describing impetigo is that you may encounter lesions at different stages of evolution simultaneously on the same patient. Because impetigo spreads by autoinoculation, a patient might have fresh vesicles or pustules on one area, fully crusted lesions on another, and healing erosions on a third. Describing these stages accurately helps convey the timeline and activity of the infection.
For non-bullous impetigo, the progression runs from erythematous macule to vesicle or pustule to ruptured lesion with honey-colored crust. Postinflammatory pigmentary changes, either hypopigmentation or hyperpigmentation, may appear as lesions heal, but scarring is uncommon.1DermNet. Impetigo If you see pigment changes at the site of older lesions alongside active crusted plaques, note both. Something like “active honey-crusted lesions on the chin with postinflammatory hypopigmentation at sites of resolved lesions on the left cheek” communicates that the infection has been present for a while and is still spreading.
For bullous impetigo, the stages run from small vesicle to enlarged flaccid bulla to ruptured erosion with collarette and thin brown crust.2PubMed Central. Pediatric Bullous Impetigo: A Case Report and Literature Review Documenting the presence of both intact and ruptured bullae on the same exam tells the reader the process is ongoing and new lesions are forming. If all bullae have ruptured and you only see erosions and collarettes, you may want to note the absence of intact blisters, since that could reflect either natural progression or the effects of treatment.
Appearance on Darker Skin Tones
Most textbook descriptions of impetigo assume a lighter skin background where erythema is easily visible, but on darker skin tones, the initial erythematous macule of non-bullous impetigo can be much harder to see.1DermNet. Impetigo This matters for exam documentation because the earliest stage of the lesion may go unrecognized or undescribed.
On brown or dark brown skin, what you may notice first is not redness but a change in skin texture, slight swelling, or the crust itself appearing against a background that looks violaceous or hyperpigmented rather than classically red. The honey-colored crust remains visible regardless of skin tone, which is one reason it is such a useful descriptor. If you are examining a patient with darker skin and see golden crusts without the expected surrounding redness, that is still consistent with impetigo. Documenting the color of the crust and the absence or subtlety of surrounding erythema is more accurate than forcing an erythema description that does not match what you are actually seeing.
Postinflammatory hyperpigmentation tends to be more pronounced and longer-lasting on darker skin, so healed impetigo sites may be more noticeable in these patients. If a patient presents with both active lesions and prominent dark patches at sites of old ones, this combination is worth documenting clearly so that the pigmentary changes are not mistaken for a separate condition.
When Impetigo Is Not Primary but Superimposed
Not every case of impetigo starts on intact skin. Secondary impetiginization, sometimes called “impetiginized” dermatitis, occurs when a pre-existing skin condition becomes colonized and infected with the bacteria that cause impetigo. This happens commonly with eczema, insect bites, scabies, and other conditions that compromise the skin barrier. On exam, you see the underlying dermatitis plus the new addition of honey-colored crusting, increased oozing, or pustules that were not part of the original condition.
A case report illustrates this well: a teenager with long-standing atopic dermatitis developed superimposed impetigo after months of topical corticosteroid use, with microbiological testing confirming Staphylococcus aureus infection on top of dyshidrotic eczema.5PubMed Central. Impetiginized Dyshidrotic Eczema Documenting this on exam requires describing both layers: the background condition and the superimposed infection. You might write “impetiginized eczematous dermatitis with honey-colored crusting overlying erythematous, lichenified plaques on the bilateral hands” rather than just documenting the crusts alone. Missing the underlying condition means missing the reason the impetigo happened in the first place and potentially the reason it keeps recurring.
A practical clue that impetigo is secondary rather than primary is the distribution pattern. Primary impetigo tends to cluster in characteristic locations as described above. When you find honey-crusted lesions in an unusual distribution that maps to an existing dermatitis, eczema flare, or known area of skin breakdown, think secondary impetiginization and document accordingly.
Separating Bullous Impetigo From Staphylococcal Scalded Skin Syndrome
One of the most clinically important distinctions to make on exam is between bullous impetigo and staphylococcal scalded skin syndrome (SSSS), because both involve superficial blistering caused by staphylococcal exfoliative toxins. The key difference comes down to local versus systemic toxin effects. Bullous impetigo results from local toxin release at the site of infection, so the blistering stays localized. SSSS occurs when those same toxins spread through the bloodstream, producing a generalized, often dramatic presentation with widespread erythema and desquamation.3PubMed Central. Staphylococcal Scalded Skin Syndrome and Bullous Impetigo
On exam, the features that help you distinguish the two are extent and associated findings. Bullous impetigo presents with localized, well-demarcated clusters of flaccid bullae without surrounding erythema or edema. SSSS produces widespread, tender erythema that can involve nearly the entire body surface, with sheets of skin peeling off and a positive Nikolsky sign, where gentle lateral pressure on the skin causes the upper layers to slide off. If you are examining a child with a few clusters of blisters on the trunk and diaper area without surrounding redness and without systemic symptoms, that pattern fits bullous impetigo. A child with diffuse erythroderma, skin tenderness, and large sheets of peeling skin is a different clinical picture entirely.
Documenting the extent and distribution carefully is what makes this distinction possible from the exam alone. Noting “well-demarcated cluster of flaccid bullae limited to the right axilla without surrounding erythema, Nikolsky sign negative” versus “diffuse erythema with superficial desquamation over the trunk and extremities, Nikolsky sign positive” paints two very different pictures for the reader of your note.
Other Conditions That Can Mimic Impetigo
Beyond SSSS, several other conditions produce crusted or blistered lesions that can be confused with impetigo on initial exam. Herpes simplex, particularly around the mouth, creates grouped vesicles on an erythematous base that can look similar to early non-bullous impetigo before the characteristic crusting develops. The key difference is that herpetic vesicles tend to be more uniform in size, grouped tightly on an erythematous plaque, and are often preceded by pain or tingling. Impetigo lesions are usually painless or only mildly uncomfortable, and they tend to evolve into the thick golden crust more quickly than herpes lesions evolve into their thinner, darker crusts.
Contact dermatitis can also produce oozing and crusting, but the distribution usually maps to an area of exposure rather than the face-and-extremity pattern of primary impetigo. Tinea corporis, or ringworm, sometimes gets confused with impetigo because of its annular morphology and peripheral scaling, but tinea typically has a well-defined, raised, scaly border with central clearing rather than honey-colored crusting. Pemphigus vulgaris produces flaccid bullae and erosions, similar to bullous impetigo, but it tends to present in adults rather than children, involves the mucous membranes, and has a more chronic course. Noting the patient’s age, the time course, mucosal involvement, and the specific morphologic features of the lesions helps narrow the differential from the exam alone.
Complications Worth Looking For
Most impetigo cases are mild and self-limited, but certain findings on exam should prompt you to look more carefully. Regional lymphadenopathy, particularly tender, enlarged nodes draining the area of infection, suggests a more significant bacterial burden and is worth documenting as part of the exam. Cellulitis, recognized by expanding erythema, warmth, and tenderness beyond the borders of the impetigo lesions, indicates deeper tissue involvement.
The most serious downstream complication of streptococcal impetigo is post-streptococcal glomerulonephritis, which can develop several weeks after the skin infection. While you will not see glomerulonephritis on a skin exam, awareness of this complication is relevant on follow-up visits. The signs to watch for include peripheral edema, hypertension, and dark or decreased urine output, reflecting the kidney inflammation and fluid retention that characterize the condition.6PubMed Central. A Comprehensive Review Study on Glomerulonephritis Associated With Post-streptococcal Infection If a patient returns weeks after an impetigo episode with facial or periorbital puffiness, checking blood pressure and urine is warranted. Documenting the original impetigo thoroughly makes it easier to connect the dots later.
Practical Tips for Clear Documentation
Describing skin findings well is partly about knowing the right terms and partly about discipline in using them consistently. A few habits make impetigo documentation more useful:
- Name the primary lesion: Start with what you see. Is it a crust, a bulla, an erosion, a vesicle? This anchors the description.
- Specify color and quality: “Honey-colored crust” is specific. “Crust” alone is vague. “Flaccid bulla with clear fluid” is more informative than “blister.”
- Note the arrangement: Are lesions grouped, scattered, or in a linear pattern suggesting autoinoculation from scratching?
- Describe distribution anatomically: Name the body regions involved rather than using vague generalizations.
- Document what is absent: The lack of surrounding erythema, the absence of mucosal involvement, a negative Nikolsky sign. These negative findings are sometimes as diagnostic as the positive ones.
- Note the stage: If you see lesions at different points in their evolution, say so. “Intact vesicles alongside older honey-crusted erosions” communicates an active, spreading infection.
One common documentation pitfall is writing the diagnosis instead of the description. Charting “impetigo on the face” tells the next reader what you think is happening, but it does not tell them what you actually saw. Charting “multiple grouped, honey-colored crusted erosions on the perioral skin and bilateral nares, without surrounding erythema or regional lymphadenopathy” tells them both. If your assessment turns out to be wrong, the descriptive note still has value because someone else can reinterpret the findings. A diagnosis-only note does not offer that safety net.