Which of the following can lead to post-inflammatory hyperpigmentation if not treated properly?

Post-inflammatory hyperpigmentation (PIH) occurs after the skin has been inflamed, and the process of healing can leave dark spots on the skin. Inflamed acne—which includes pustules, papules, and cysts—triggers this inflammatory response in the skin. When these types of acne lesions are not treated properly, the inflammation can damage the skin and lead to an increase in melanin production as part of the healing process, resulting in hyperpigmentation.

While inactive acne or other types of acne might also impart some risk of PIH, they do not carry the same level of inflammatory response that inflamed acne does. Inactive acne is typically not associated with the same degree of skin trauma or inflammation. Therefore, it's the inflamed acne that is particularly significant in leading to post-inflammatory hyperpigmentation if not properly managed. This highlights the importance of addressing inflamed lesions effectively to mitigate the risk of PIH in clients.