When a pimple goes away, why does it take so long for that lingering pinkish-red spot to fade? This phenomenon is technically called post-inflammatory erythema. With the help of dermatologist Sandra Lee, MD (aka Dr. Pimple Popper), we’re answering all of your questions: what causes those red spots to form in the first place, why some of them turn brown, and most importantly, what you can do to treat and prevent post-inflammatory erythema.