Untreated acne usually lasts about 4-5 years before settling. However, it can last for many years in some cases with visible marks and scars varying in severity.
On a short-term basis, each inflamed spot will heal eventually, however, in some cases, the area of skin that was inflamed remains discoloured for several months after the inflammation has gone (post-inflammatory hyperpigmentation). This is often more noticeable in darker-skinned people.
On a long-term basis, a small pitted scar is commonly left on the skin where there was an inflamed spot. These small scars often do not fade fully and are a marker in older people that they once had inflamed acne spots. This is why it is advisable to not let acne run it’s own course, rather have it treated to minimise it’s presence and therefore, reduce long term damage caused.