Lesions are any area of abnormal tissue, and they vary enormously in appearance depending on their type, cause, and location. On the skin, a lesion can be as subtle as a flat discolored spot or as obvious as a raised, fluid-filled blister. Inside the body, lesions show up on imaging scans as areas that look different from surrounding tissue. Understanding the basic visual categories helps you describe what you’re seeing and recognize when something needs attention.
The Basic Types of Skin Lesions
Skin lesions fall into a handful of categories based on three things: whether they’re flat or raised, how big they are, and whether they contain fluid.
- Macules are flat spots, usually under 10 mm across. They’re purely a color change: you can see them but can’t feel them by running your finger over the skin. Freckles and flat moles are common examples.
- Papules are small bumps, also under 10 mm, that you can feel when you touch them. A mosquito bite or a small acne bump is a papule.
- Nodules are firm lumps that sit deeper in the skin. They feel solid and extend below the surface. A cyst you can feel under the skin is a typical nodule.
- Vesicles are small fluid-filled blisters under 10 mm. When they’re larger than that, they’re called bullae. A cold sore or a chickenpox blister is a vesicle.
These categories matter because they give you a precise way to describe what you’re looking at. Telling a provider “I have a raised bump I can feel” (papule) communicates something very different from “I have a flat discolored spot” (macule).
How Infectious Lesions Differ
Bacterial and viral infections each produce characteristic-looking lesions. Impetigo, a common bacterial infection, causes red sores that weep and then dry into a honey-yellow crust. Cellulitis looks different: it creates a spreading area of redness and swelling that feels warm and painful to the touch, often without distinct borders.
Viral lesions tend to follow different patterns. Shingles produces clusters of painful, burning blisters that typically appear in a band along one side of the body. Measles causes a widespread rash of flat and slightly raised spots that spreads from the face downward. Herpes simplex creates small, grouped vesicles that rupture and crust over within a few days.
Regardless of cause, skin infections share some common visual cues: redness (or, on darker skin tones, purple or darkened areas), swelling, and sometimes warmth. Signs that an infection is becoming severe include pus, blistering, skin that’s breaking down, or dark areas that suggest tissue is dying.
Psoriasis and Eczema Plaques
Two of the most common chronic skin conditions produce lesions that look similar at first glance but have key differences. Psoriasis tends to create thick, well-defined plaques covered in silvery or whitish scales. These usually appear on the outer surfaces of joints, particularly the elbows and knees. The borders are relatively sharp, and the patches often look raised and clearly distinct from surrounding skin.
Eczema (atopic dermatitis) typically shows up in the opposite locations: the inner creases of elbows, behind the knees, and on the neck. The patches are dry, itchy, and less sharply bordered than psoriasis. Eczema can also present as small bumps or even fluid-filled blisters, especially during flare-ups. The skin often looks rough and may crack or weep when scratched.
What Mouth Lesions Look Like
Lesions inside the mouth have their own visual signatures. Canker sores (aphthous ulcers) are painful, shallow ulcers with a yellow or whitish base surrounded by a red halo. They typically appear on soft tissue like the inner lips, cheeks, tongue, or soft palate. Traumatic ulcers from accidentally biting your cheek look similar, with redness and swelling around a central area covered by a yellowish-white film.
Oral squamous cell carcinoma, the most common form of mouth cancer, looks quite different. It usually presents as a sore that simply won’t heal. The edges tend to be irregular, firm, and rolled or raised rather than flat. If you have an ulcer in your mouth that persists for more than two to three weeks without improvement, that’s worth getting evaluated.
Warning Signs of Melanoma
The National Cancer Institute uses the ABCDE rule to describe the visual features of a mole or spot that could be melanoma:
- Asymmetry: one half of the spot doesn’t match the other half in shape.
- Border: the edges are ragged, notched, or blurred, and pigment may spread into surrounding skin.
- Color: instead of one uniform shade, you see a mix of brown, black, tan, white, gray, red, pink, or blue within the same spot.
- Diameter: most melanomas are larger than 6 millimeters across (roughly the size of a pencil eraser), though they can be smaller.
- Evolving: the spot has changed in size, shape, or color over recent weeks or months.
A normal mole is typically round or oval, one consistent color, and stable over time. Any mole that breaks one or more of these rules deserves a closer look from a dermatologist.
How Lesions Look on Medical Imaging
Internal lesions, the kind found in organs like the liver, kidneys, or brain, can’t be seen with the naked eye. They show up on CT scans, MRIs, or ultrasounds as areas that look different from the normal tissue around them.
A radiologist might describe a finding as “hypoattenuating,” which means it appears darker or less dense than the organ it’s in. This often turns out to be a simple fluid-filled cyst, which is extremely common and usually harmless. An “enhancing lesion” is one that brightens when contrast dye is injected, meaning it’s solid rather than fluid-filled. Most enhancing lesions found incidentally in people with no cancer history are still benign, but they sometimes require follow-up testing to rule out something more serious.
You may also see the phrase “too small to characterize” in a radiology report. This simply means the lesion is so tiny that the radiologist can’t determine exactly what it is from the scan alone. In most cases, these are harmless cysts spotted by chance.
How Lesions Change as They Heal
A skin lesion that’s healing goes through visible stages. Early in the healing process, new tissue called granulation tissue fills the wound. This tissue looks pink or red and has an uneven, bumpy texture. It typically doesn’t bleed, and its presence is a good sign that your body is actively repairing itself.
As healing continues into the maturation stage, the new tissue starts out looking pink, wrinkled, or stretched. Over time, it fades in color and flattens out. The tissue strengthens through a process of internal restructuring, and any scar generally becomes thinner and less noticeable, though some degree of scarring often remains permanently.
A lesion that isn’t healing normally may scab over repeatedly without ever progressing past that point. If a wound fails to form new tissue, keeps reopening, or shows no improvement over several weeks, it may have become a chronic wound that needs professional treatment to move forward.