The difference between PIH vs PIE is not just down to the colour of the acne marks, but how these acne marks are caused. Both PIH and PIE are caused by inflammation or skin injury. However, in PIH, this inflammation causes an increase in the production of pigment. Specifically, melanin is overproduced by melanocytes (melanin-producing cells) and transferred to surrounding keratinocytes (skin cells).
In contrast, PIE results are due to the blood vessel dilation associated with wound healing. The appearance of this is worsened by the fact that the skin is thinner during the healing process. Some evidence also suggests that acne is associated with skin barrier dysfunctions and that the residual erythema associated with PIE is largely due to damage and dehydration in the skin's outermost layer – the stratum corneum.
Another difference between PIH vs PIE may be purely down to the type of melanin produced in response to inflammation. Two basic types of melanin are found in human skin; eumelanin and pheomelanin. Eumelanin is the type of melanin that springs to mind when discussing pigmentation as it is brown/black, more prevalent in darker skin types, and has a photoprotective effect. Pheomelanin, on the other hand, is yellow/reddish, is more prevalent in fairer skin types, is photo-unstable, and may even promote skin cancer. In this sense, the difference between PIH vs PIE may simply be down to the different types of melanin expressed by different skin types.
First things first, it is important to ensure that active acne is treated before trying to improve the appearance of acne scars, otherwise, new scars will continue to form. The early treatment of active acne remains the most effective way to prevent or reduce acne scarring. The current treatment for atrophic acne scars usually requires procedures such as laser resurfacing, dermabrasion, microneedling, radiofrequency, dermal fillers, or subcision and excisional techniques (cutting under the scar or cutting out the scar). Some laser treatments can help improve the appearance of PIE and PIH acne marks as well.
