Final answer:
Lesions within hair follicles that become erythematous and painful are known as folliculitis, which is an inflammation of the hair follicles and can require medical treatment if persistent.
Step-by-step explanation:
Lesions that develop within hair follicles, producing papules that become erythematous and painful are termed folliculitis. Folliculitis results from the inflammation of hair follicles. It may present as itchy, red, and occasionally pus-filled bumps. Folliculitis can be caused by a variety of factors including sweat, skin injuries, ingrown hairs, tight clothing, and irritation from shaving. The condition often resolves on its own but may require medical treatment if it persists. Folliculitis differs from acne vulgaris, which is a skin condition involving the clogging of hair follicles with sebum and dead skin cells, sometimes leading to the growth of Propionibacterium acnes and the development of inflammatory lesions.