Which term refers to a skin lesion containing trapped masses of sebum?

The term that refers to a skin lesion containing trapped masses of sebum is "comedo." A comedo is essentially what is commonly known as a blackhead or whitehead, depending on whether the follicle is open or closed. In the case of a blackhead, the sebum and dead skin cells within the follicle oxidize and darken, while a whitehead results when the follicle is closed and not exposed to air.

This condition arises when excess sebum production, often influenced by hormonal changes, clogs the hair follicle. Understanding the nature of a comedo is crucial for skin care because appropriate treatment can help prevent acne formation. The other terms listed are related to skin conditions but do not describe lesions specifically characterized by trapped sebum. For instance, dermatitis refers to inflammation of the skin, rosacea is a chronic condition that mostly affects the face, characterized by redness and visible blood vessels, and keratosis is a condition involving the thickening of the outer layer of the skin.