A pimple pops up due to specific blockage in the skin pores. These pore blocks tend to occur during the teenage years. Thus, when the sebaceous gland becomes clogged and infected, it usually results in a swollen, red-colored wound filled with puss. Basically, pimples are a type of inflammation of the skin. Genetic factors are not always caused pimples.
Acne occurs due to an increased stimulation of androgens. Acne is a long-lasting skin condition that triggers when the hair follicles get clogged with dead skin cells and sebum. Acne can appear on the face, neck, shoulders, chest and back. Individuals affected by acne will often present with comedones, papules, pustules, and scarring. Acne can be caused by genetic factors.
Source: Procter & Gamble and Pediaa