What constitutes a pustule on the skin?

A pustule on the skin is characterized by a raised, inflamed area that contains pus, often appearing as a white or yellowish center surrounded by redness. This formation is primarily due to an accumulation of white blood cells responding to infection or inflammation, which gives the pustule its characteristic appearance.

The presence of pus is key to defining a pustule; it indicates that there has been an immune response, often due to bacteria, which leads to the formation of pus as a mixture of dead cells, bacteria, and immune cells. Therefore, the description highlighting a clump of white blood cells that has surfaced aligns closely with the medical understanding of a pustule and clarifies its nature as a skin lesion commonly associated with conditions like acne.

In contrast, other options refer to different skin features. For instance, a raised area smaller than 1 centimeter describes a papule, while a red blemish with no pus indicates a macule or some inflammatory condition without purulent content. Lastly, a dried-up acne lesion would likely refer to a crust or scab left after a pimple has resolved, rather than being indicative of a pustule itself. Understanding these distinctions is crucial for accurately identifying skin conditions in esthetics and dermatology.