How to Describe a Rash or Primary Lesion

Primary Lesions - Papule

Multiple red papules on the wrists. CDC/ Susan Lindsley

A primary lesion is a basic lesion that makes up a rash. Identifying the primary lesion of a rash is the first step towards identifying the rash.

A papule is an elevated, solid lesion that measures less than 0.5cm. Papules are the most common type of primary lesion. They can be any color.

Primary Lesions - Macule

Multiple Red Macules. CDC

A macule is a flat discoloration that has a definite border. It can be brown, blue, red, or lighter than the surrounding skin.

Primary Lesions - Nodule

Nodules around the elbow - yaws. CDC/ Dr. Peter Perine

A nodule is a raised, solid lesion that is greater than 0.5 cm in diameter. A large nodule is called a tumor but there are no size criteria that distinguish a nodule from a tumor.

Primary Lesions - Pustule

Pustule under the eye. CDC

A pustule is an elevated lesion of any size that contains pus.

Primary Lesions - Plaque

Several plaques on the arm. CDC/ Dr. N.J. Fiumara

A superficial, solid, elevated lesion that is greater than 0.5 cm in diameter. A plaque is often formed when multiple papules merge.

Primary Lesions - Vesicle

A single vesicle on the back. CDC

A vesicle is a raised lesion that is filled with fluid and is less than 0.5 cm in diameter.

Primary Lesions - Bulla

Bulla on back. CDC

A bulla is a raised lesion that is greater than 0.5 cm in diameter and contains clear fluid. Bullae can get very large and are often subclassified as tense or flaccid depending on how full they are.

Primary Lesions - Wheal

A wheal on the arm. CDC/ Dr. William Foege

A wheal is a firm, spongy lesion formed when the ​dermis is filled with fluid. A ​wheal will typically last for a very short time - up to hours - then disappear.

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