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PIE vs PIH – Or “why did this acne spot leave a mark?”

Perhaps the worst part about acne is not simply having the spot itself, but that the spot remains red or brown for a long period of time after the initial spot has been… ahem… dealt with.

For many, these spots of discoloration hang around for weeks or even months after, and depending on the severity of the initial breakout, can be pretty bright or noticeable. My skin is still fading three or four marks from my last big breakout around Christmas (jaw and upper lip acne is so flattering during the ‘Happiest Time of the Year’) and I still have a dark red spot on my left cheek from an over-ambitious romp I had with a cleanser back in March.

So what is it that causes these spots? What are they? And how do we fade them?


When our skin erupts into an acne spot, it inflames and causes trauma to the skin around it (this is why it is even more important not to pick or squeeze spots hard – you’re causing even more damage to occur). This trauma in the skin results in an erythema — a superficial reddening of the skin as a result of dilation (or increased blood flow) of the capillaries.

Skin erythema can occur with infections, rashes (such as Lyme’s disease), sunburns, allergic reactions, allergies, and yes, you guessed it — acne. This reddening of the skin after an acne spot is referred to as post-inflammatory erythema or PIE.

It generally occurs in people with fairer skin tones (I’ll get to darker skin tones in a second!) and appears red or pink — not brown. Over time, these pink or reddish spots can turn brown, which is post-inflammatory hyperpigmentation or PIH.


Post-inflammatory erythema

The primary difference between post-inflammatory erythema (PIE) and post-inflammatory hyperpigmentation (PIH) is that the redness disappears (called blanching)  once pressure is applied to the area.

Post-inflammatory hyperpigmentation is more common in people with darker skin tones, and occurs when the body produces melanin as a result of inflammation or injury.


Post-inflammatory hyperpigmentation

This is why treatments for resolved acne spots for darker skin tones does not typically work for people with lighter skin tones and vise versa. However, PIE can become darkened, as I said above, and turn into PIH. This usually happens when the skin is exposed to UV (sun), especially in short does over long periods of time (such as driving to work).

Treatment Options

Both PIE and PIH usually disappear on their own, but can take weeks, months, or even years. There are a couple options to speed up the process.

PIE Treatment

  • Pulsed Dye Lasers. Similar to IPL (or Intense Pulsed Light), PDL aims intense light at blood vessels beneath the skin. This light is absorbed by abnormal blood vessels and converts to heat, which destroys the vessels without damaging the surrounding skin. It can cause bruising, and can take multiple sessions if lesions are larger or very numerous. PDL is usually recommended for severe spots, and can be used to treat a variety of conditions, from stretch marks to port wine stains. [PHOTOSTW: Images of self-harm scars and burns]
  • Coverage and wait. Protecting PIE spots from UV damage shortens their lifespan and ensures they don’t turn into PIH. Anecdotally, I have had better luck with PIE spots when I do not pick or pop the spot and keep the area moisturized before, during, and after resolution of the spot.

PIH Treatment

  • Topical Vitamin C. Since PIH is hyperpigmentation, most antioxidant treatments that are formulated to target hyperpigmentation will help resolve post-inflammatory hyperpigmentation. Topical vitamin C products are great for this, and L-AA (L-Absorbic Acid, a form of vitamin C) serums especially. Timeless is a trustworthy brand that can be found on Amazon.
  • AHAs and Azelaic Acid. I’ve made a longer post on hydroxy acids (how they work, what they require for efficacy, et cetra.). You can read about them here. More specifically, glycolic, lactic, mandelic, and azelaic acid are all effective for fading PIH marks.
  • Skin brighteners. Arbutin, licorice, and niacinamide are wonderful skin brightening ingredients that are found in a plethora of products these days, particularly products created for the Asian skincare market. They are typically non-irritating (though niacinamide can irritate some sensitive skins in higher percentages, such as 5-10%). Some product examples:


  1. Easy as PIE
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