What Is Post Inflammatory Erythema?
Post inflammatory erythema, or PIE, is the red or pink marks left on the skin after inflammation goes away, like from a pimple or acne breakout. It happens when tiny blood vessels near the skin’s surface get damaged or widened during healing, making the area look reddish instead of the original skin color.[1][2][3]
This is different from dark spots called post inflammatory hyperpigmentation, or PIH. PIE shows up mostly on lighter skin tones as flat red, pink, or sometimes purple patches. PIH appears as brown or dark spots on medium to deeper skin tones because of extra pigment called melanin.[1][3]
Acne is the top cause of PIE, especially cystic acne that causes strong inflammation. The skin fights the infection with immune cells, but this can hurt nearby capillaries, the small blood vessels. Things like histamine and other chemicals make these vessels dilate, or open up wider, so more blood flows through and creates redness.[2][3]
PIE can also come from other skin issues. These include eczema, allergic reactions, bug bites, cuts, too much sun, or hormone changes. Any event that irritates the skin and sparks swelling can lead to it.[1][2]
The redness sticks around because the damaged vessels take time to heal. In some cases, new blood vessels form, which keeps the pink hue going even after the main inflammation stops.[2] How long it lasts depends on how bad the first inflammation was and how fast your skin repairs itself. Mild cases fade in weeks, but tougher ones can linger for months.[3]
PIE is a type of erythema, which just means any skin redness from irritated or expanded superficial blood vessels.[4] It is not about pigment changes, so treatments focus on calming vessels and reducing leftover swelling, not bleaching color.
Sources
https://banish.com/blogs/article/pie-vs-pih-how-to-tell-the-difference
https://www.kins-clinic.com/blogs/post-inflammatory-erythema-from-acne-a-guide-to-causes-and-treatments
https://moawadskininstitute.com/post-inflammatory-erythema-cure/
https://www.britannica.com/science/erythema
