What type of lesion is a large protruding pocket-like formation filled with sebum?

A sebaceous cyst is a type of lesion characterized as a large protruding pocket-like formation that is filled with sebum, which is an oily substance produced by sebaceous glands in the skin. These cysts often develop when a sebaceous gland becomes blocked, causing sebum to accumulate inside. They can be firm to the touch and may vary in size.

Unlike other lesions mentioned, such as papules, which are small, raised lesions typically associated with acne or other skin conditions, or warts, which are caused by viral infections and appear as rough, raised growths, sebaceous cysts are specifically filled with sebum and arise from sebaceous glands. Comedones, such as blackheads or whiteheads, refer to clogged hair follicles but are not pocket-like formations and are much smaller. Thus, recognizing the defining characteristics of a sebaceous cyst is key in distinguishing it from other types of skin lesions.