A skin lesion is a superficial growth or patch of the skin that does not resemble the area surrounding it.
Skin lesions can be grouped into two categories: primary and secondary. Primary skin lesions are variations in color or texture that may be present at birth, such as moles or birthmarks, or that may be acquired during a person's lifetime, such as those associated with infectious diseases (e.g., warts, acne, or psoriasis), allergic reactions (e.g., hives or contact dermatitis), or environmental agents (e.g., sunburn, pressure, or temperature extremes). Secondary skin lesions are those changes in the skin that result from primary skin lesions, either as a natural progression or as a result of a person manipulating (e.g., scratching or picking at) a primary lesion.
The major types of primary lesions are:
Macule. A small, circular, flat spot less than 0.4 in (1 cm) in diameter. The color of a macule is not the same as that of nearby skin. Macules come in a variety of shapes and are usually brown, white, or red. Examples of macules include freckles and flat moles. A macule more than 0.4 in (1 cm) in diameter is called a patch.
Vesicle. A raised lesion less than 0.2 in (5 mm) across and filled with a clear fluid. Vesicles that are more than0.2 in (5 mm) across are called bullae or blisters. These lesions may may be the result of sunburns, insect bites, chemical irritation, or certain viral infections, such as herpes.
Pustule. A raised lesion filled with pus. A pustule is usually the result of an infection, such as acne, imptigeo, or boils.
Papule. A solid, raised lesion less than 0.4 in (1 cm) across. A patch of closely grouped papules more than0.4 in (1 cm) across is called a plaque. Papules and plaques can be rough in texture and red, pink, or brown in color. Papules are associated with such conditions as warts, syphilis, psoriasis, seborrheic and actinic keratoses, lichen planus, and skin cancer.
Nodule. A solid lesion that has distinct edges and that is usually more deeply rooted than a papule. Doctors often describe a nodule as "palpable," meaning that, when examined by touch, it can be felt as a hard mass distinct from the tissue surrounding it. A nodule more than 0.8 in (2 cm) in diameter is called a tumor. Nodules are associated with, among other conditions, keratinous cysts, lipomas, fibromas, and some types of lymphomas.
Wheal. A skin elevation caused by swelling that can be itchy and usually disappears soon after erupting. Wheals are generally associated with an allergic reaction, such as to a drug or an insect bite.
Telangiectasia. Small, dilated blood vessels that appear close to the surface of the skin. Telangiectasia is often a symptom of such diseases as rosacea or scleroderma.
The major types of secondary skin lesions are:
Ulcer. Lesion that involves loss of the upper portion of the skin (epidermis) and part of the lower portion (dermis). Ulcers can result from acute conditions such as bacterial infection or trauma, or from more chronic conditions, such as scleroderma or disorders involving peripheral veins and arteries. An ulcer that appears as a deep crack that extends to the dermis is called a fissure.