Skin lesions represent any abnormal change that appears on or within the skin. These changes can vary widely in appearance, from alterations in color or texture to raised bumps or fluid-filled sacs. Recognizing these differences is the initial step in understanding potential skin conditions. Skin lesions can result from injuries, infections, or underlying health issues.
Defining Primary Lesions
Primary lesions are the initial manifestations of a disease process or pathological change occurring in the skin. They emerge on previously normal, healthy skin and are not altered by external factors or complications, making them characteristic indicators of a particular condition. Identifying primary lesions provides important diagnostic insights for dermatologists.
Common Types of Primary Lesions
Macule
A macule is a flat, discolored spot on the skin less than 1 centimeter (cm) in diameter. It represents a change in skin color without elevation or depression. Examples include freckles or flat moles.
Patch
A patch is essentially a larger macule, defined as a flat, discolored area of skin greater than 1 cm in diameter. Like macules, patches involve only a change in skin color, and texture remains unaffected. Vitiligo, a condition causing areas of lost skin pigment, is a common example.
Papule
A papule is a small, raised, solid bump on the skin less than 1 cm in diameter. These lesions are palpable, meaning they can be felt when touched. Warts and moles are common examples of papules.
Plaque
A plaque is an elevated, solid lesion larger than 1 cm in diameter, often with a flat top. Plaques can be formed by the merging of multiple papules and may appear scaly. Psoriasis, characterized by thick, silvery scales, frequently manifests as plaques.
Nodule
A nodule is a solid, elevated lesion larger than a papule, often exceeding 1 cm in diameter, and extends deeper into the skin layers. These lesions are firm and can involve the dermis or subcutaneous tissue. Fibromas are common examples of nodules.
Tumor
A tumor, in dermatology, refers to a large nodule or mass greater than 2 cm in length that can be solid and elevated. A lipoma, a benign fatty growth, exemplifies a tumor in this context.
Wheal
A wheal is a transient, elevated, and often itchy lesion resulting from swelling in the skin. These lesions, also known as hives or welts, can vary in size and shape and usually appear suddenly. They commonly arise from allergic reactions or insect bites.
Vesicle
A vesicle is a small, fluid-filled blister on the skin less than 0.5 cm or 1 cm in diameter. The fluid inside is clear. Conditions like herpes simplex can cause vesicles.
Bulla
A bulla is a large fluid-filled blister, defined as greater than 0.5 cm or 1 cm in diameter. Like vesicles, bullae contain clear fluid but are significantly larger. Bullous pemphigoid, an autoimmune skin disorder, is characterized by the presence of bullae.
Pustule
A pustule is a small, elevated lesion that contains pus. These lesions can be white or yellow and are often seen in conditions like acne. Not all pustules are infectious, as seen in pustular psoriasis.
Cyst
A cyst is a sac-like lesion within the skin that contains fluid or semi-solid material. Cysts can feel fluctuant, meaning they have a yielding or wavy feel when pressed. A sebaceous cyst, which forms from blocked oil glands, is a common example.
Distinguishing Primary from Secondary Lesions
The distinction between primary and secondary lesions is based on their origin and evolution. Secondary lesions, in contrast, develop from primary lesions or are caused by external factors such as scratching, infection, or the natural healing process. They represent a modification of the original skin change.
For instance, a primary lesion like a vesicle, a small fluid-filled blister, might rupture due to scratching. This rupture can then lead to a secondary lesion, such as an erosion or a crust. Similarly, repeated scratching of an itchy papule can result in excoriation, a linear scratch mark.
Common secondary lesions include:
Crusts (dried fluid)
Scales (flaky skin)
Erosions (shallow depressions)
Ulcers (deep open sores)
Fissures (cracks in the skin)
Scars (fibrous tissue after injury)
Atrophy (thinning of the skin)
Lichenification (thickening due to chronic rubbing)
Understanding this progression helps healthcare professionals diagnose and manage skin conditions.