Which of the following is true about a comedo?

A comedo is specifically a type of sebaceous pore that can indeed manifest as either a blackhead or a whitehead. When the follicle is open to the skin’s surface, the material inside (which includes sebum and dead skin cells) oxidizes and darkens, forming what is known as a blackhead. Conversely, when the follicle is closed, the material is not exposed to air, which keeps it lighter in color and causes it to be classified as a whitehead. This dual presentation is a hallmark of comedones, making the identification of their appearance critical for anyone studying skin lesions or dermatological conditions.

While lesions associated with cysts, collections of pus, and fissures are relevant medical concepts, they do not accurately describe what a comedo is or how it functions in relation to acne or skin health. Therefore, the correct choice clearly reflects the nature of a comedo in dermatological terminology.