Pimples vary based on whether they are open to the air and the level of inflammation involved:

Acne: Types, Causes, Treatment & Prevention - Cleveland Clinic

Pimples are small, often inflamed skin growths that develop when with a mixture of excess oil (sebum), dead skin cells, and bacteria . Most common on the face, chest, and back, they are a primary symptom of acne vulgaris , the most widespread skin condition affecting approximately 80% of people at some point in their lives. Common Types of Pimples