Describing skin lesions accurately means using a systematic approach that covers morphology, size, color, shape, borders, arrangement, and distribution. Whether you’re a nursing student learning clinical documentation, a medical student preparing for rotations, or anyone who needs to communicate what a skin finding looks like, the same structured vocabulary applies. Master the terminology below and you can describe virtually any lesion clearly enough that someone who hasn’t seen it can picture it.
Primary Lesions: The Starting Point
Primary lesions are the ones that appear first, directly caused by a disease process. They haven’t been scratched, infected, or otherwise altered. Identifying the primary lesion is the single most important step in describing what you see, because it narrows the possible diagnoses more than any other feature.
The key distinction is between flat lesions, raised solid lesions, and fluid-filled lesions. Within each group, size is the dividing line:
- Macule: A flat, non-palpable spot of color change, less than 10 mm across. A freckle is a macule. You can see it but not feel it with your fingertip.
- Patch: A flat area of color change larger than 10 mm. Essentially a big macule.
- Papule: A small, solid, raised bump less than 10 mm. You can feel it when you run your finger over the skin. A wart or a small acne bump qualifies.
- Plaque: A raised, plateau-like area larger than 10 mm. Psoriasis patches are the classic example. Think of it as a broad, flat-topped elevation.
- Nodule: A firm, solid lesion that extends deeper into the skin, up to about 2 cm. It has depth you can feel, unlike a papule that sits more on the surface.
- Vesicle: A small, fluid-filled blister less than 10 mm. Cold sores from herpes simplex are vesicles.
- Bulla: A fluid-filled blister larger than 10 mm. Same concept as a vesicle, just bigger.
- Pustule: A small, raised lesion filled with pus rather than clear fluid, less than 10 mm. The white-headed pimple on your chin is a pustule.
The 10 mm cutoff (about 1 cm) is the threshold that matters most. Flat and small means macule. Flat and large means patch. Raised, solid, and small means papule. Raised, solid, and large means plaque. Fluid-filled and small means vesicle. Fluid-filled and large means bulla. Memorize those pairs and you have the foundation.
Secondary Lesions: What Happens Next
Secondary lesions evolve from primary lesions. They result from scratching, healing, infection, or natural progression. Describing them tells the reader what has happened to the skin over time.
- Scale: Flaky, peeling fragments of the outer skin layer. Dandruff and psoriasis plaques both produce scale.
- Crust: Dried fluid (serum, blood, or pus) on the surface. The golden crust on impetigo is a textbook example.
- Erosion: A shallow loss of skin that doesn’t extend past the outer layer. It heals without scarring.
- Ulcer: A deeper open sore that extends below the outer skin layer. Unlike erosions, ulcers can scar.
- Fissure: A linear crack in the skin, often painful. Dry, cracked heels are fissures.
- Excoriation: A scratch mark, usually from the patient’s own fingernails. Seeing excoriations tells you the lesion itches.
- Atrophy: Thinning of the skin, which looks wrinkled or translucent. Long-term steroid cream use is a common cause.
When you’re writing a description, note both the primary and secondary features. A plaque with overlying silvery scale immediately suggests psoriasis. A vesicle with surrounding crust suggests a blister that has partially ruptured and dried.
Color: More Than Just “Red”
Color is one of the most diagnostically useful details you can include. Be as specific as possible. Rather than writing “red,” specify whether it’s bright red, dusky red, salmon-pink, or violaceous (a blue-purple hue). A violaceous papule points toward different conditions than a bright red one.
Other color terms worth knowing: erythematous means red or pink, hyperpigmented means darker than the surrounding skin, hypopigmented means lighter, and depigmented means completely lacking color (white). Purpuric refers to a deep red or purple color caused by bleeding under the skin that does not blanch (fade) when you press on it.
Color on Darker Skin Tones
Standard dermatology descriptions were historically built around lighter skin, and that creates real blind spots. On darker skin, redness often appears as reddish-brown, violet, gray, or deeply darkened areas rather than bright red. A condition like eczema that looks pink on lighter skin may show up as barely visible darkening or as areas of lighter skin on someone with more melanin.
Psoriasis in darker-skinned patients tends to produce thicker plaques with more scaling and less obvious redness. Lichen planus, which classically looks violet on lighter skin, may appear deeply dark with prominent post-inflammatory hyperpigmentation. In fact, post-inflammatory color changes (both darkening and lightening) are more common and more visible on darker skin. Noting these differences matters because missing subtle erythema on dark skin leads to delayed diagnoses.
Shape, Borders, and Configuration
After identifying the lesion type and color, describe its shape and edges. Borders can be well-demarcated (sharp, easy to see where the lesion ends and normal skin begins) or ill-defined (blurring gradually into surrounding skin). Well-demarcated borders are typical of psoriasis. Ill-defined borders are more common in eczema. This single detail can help distinguish between the two.
Shape terms describe what individual lesions look like from above. Round (circular), oval, and irregular are straightforward. Annular means ring-shaped, with clearing in the center, as in ringworm. Serpiginous means winding or snake-like. Targetoid means concentric rings, like a bullseye.
Configuration describes how multiple lesions relate to each other:
- Linear: Arranged in a line. Poison ivy rashes often streak in a linear pattern where the plant dragged across skin.
- Grouped (herpetiform): Clustered together. Herpes simplex vesicles typically cluster in a tight group.
- Dermatomal (zosteriform): Following the path of a single nerve. Shingles is the classic example, producing a band of vesicles that wraps around one side of the body.
- Reticular: A net-like or lace-like pattern.
- Scattered: Randomly spread without a clear pattern.
- Confluent: Individual lesions merging together into larger areas.
Distribution: Where on the Body
Where lesions appear is just as important as what they look like. A rash limited to sun-exposed areas (face, neck, forearms, backs of the hands) is called photodistributed and points toward sun-related conditions or drug reactions triggered by light. A rash in skin folds (armpits, groin, under the breasts) is described as intertriginous and suggests fungal infection, irritation from moisture, or inverse psoriasis.
Other distribution terms include acral (on the hands and feet), truncal (on the torso), extensor (on the outer surfaces of elbows and knees, common in psoriasis), and flexural (on the inner surfaces, common in eczema). Note whether the distribution is symmetric (both sides of the body) or unilateral (one side only), generalized (widespread) or localized (confined to one area).
Putting a Full Description Together
A good skin lesion description follows a consistent order. Think of it as building a sentence from a template: number, distribution, configuration, color, secondary changes, primary morphology, and size. In practice, it sounds like this:
“Multiple scattered erythematous, scaly papules and plaques, ranging from 5 mm to 3 cm, on the extensor surfaces of both elbows and knees.”
That single sentence tells you there are many lesions, they’re spread out, they’re red with flaking skin on top, some are small bumps and others are larger flat-topped elevations, and they’re in a symmetric pattern on the outer elbows and knees. Without ever naming a diagnosis, the description paints a clear picture of psoriasis.
Another example: “A solitary, well-demarcated, annular plaque with a raised erythematous border and central clearing, approximately 2 cm in diameter, on the right forearm.” That’s ringworm, described precisely enough that anyone reading it could picture the lesion and arrive at the same conclusion.
Common Mistakes to Avoid
The most frequent error is jumping to a diagnosis instead of describing what you actually see. Writing “looks like eczema” gives the reader your interpretation but not the evidence. If you’re wrong, the description is useless. A morphological description (“ill-defined, erythematous, scaly patches on the antecubital fossae”) stands on its own regardless of the final diagnosis.
Another common mistake is confusing primary and secondary lesions. If a vesicle has ruptured and crusted over, the primary lesion is the vesicle. The crust is secondary. Describing only the crust misses the key finding. Look at the freshest, least-altered lesions to identify the primary morphology, then note the secondary changes separately.
Finally, vague size estimates weaken a description. “Small bump” means different things to different people. Measuring in millimeters or centimeters, or comparing to a familiar object (grain of rice, pencil eraser, coin), gives the reader something concrete. When multiple lesions are present, note the size range.