Posted by

This week, let’s take a deep look at the albatross hanging around the neck of many skincare addicts: long-term discoloration caused by acne. Note: I don’t use any images in this article, because I don’t feel comfortable using people’s faces without their permission. If you’re curious what any skin condition looks like, feel free to google it.

There are three types of long-term physical changes caused by an acne lesion: postinflammatory hyperpigmentation (PIH), postinflammatory erythema (PIE), and acne scars. Acne scars have a different texture than the surrounding skin, and are either raised or lowered. I’ll leave those for another post.

PIH and PIE are two different kinds of discoloration resulting from the inflammation of an acne lesion. PIH and PIE spots appear on otherwise normal skin (e.g. no change in texture).

Postinflammatory Hyperpigmentation (PIH)

I’ll spend most of this post dealing with PIH, since it’s way more studied and documented than PIE. PIH appears after inflammation – in our case, after a pimple heals – and is caused by a deposit of excess melanin. Scientists aren’t 100% sure why this happens, but it’s likely that the skin’s inflammation response triggers melanogenesis, or the process of creating new melanin.

(Melanin is the pigment whose concentration determines our skin tone. Caucasian people have less melanin, while people of African descent have way more.)

Because melanin is brown or black, postinflammatory hyperpigmentation will appear somewhere between tan/light brown to almost black. PIH is much more likely to affect people of color, since their skin has a lot more melanin to begin with. It’s been studied in depth, and there are a lot of great treatment options, although PIH will normally fade on its own within 6-12 months.

Postinflammatory Erythema (PIE)

This is a brand spanking new term (seriously, it was coined in 2013) to describe pink or red spots that linger after an acne lesion heals. PIE consists of “discrete erythematous macules” – that is, little spots of redness caused by damage or dilation of capillaries under the skin.

Because it’s such a new concept, there’s not much in the way of treatment. The only thing I could find was pulsed dye laser treatment, which a dermatologist would do for you. Fortunately, like PIH, PIE will fade on its own over time.

The Difference Between PIH and PIE

Researching this article was a little bit of a mind-blow for me. For as much as I pamper my skin, and for as many PIH-targeting products and ingredients I use, my (what I thought was) PIH has been very slow to fade. Turns out I don’t have PIH at all, I have PIE, and there’s nothing I can do about that.

Basically, PIH will fall on the color scale from tan to dark brown, and is way more likely to affect people of color. PIE is pink or red, and is more likely to affect light-skinned folks. All the treatment options for PIH focus on inhibiting or destroying melanin, which makes sense for a condition caused by an excess of melanin (PIH). Unfortunately, melanin plays a 0% role in PIE, so none of that is gonna help.

The more you know.

Fading PIH

There are a few ways to fade PIH. The first and MOST IMPORTANT is sunscreen. PIH is caused by excess melanin production. Guess what else causes melanin production? THE SUN. THE ANSWER IS THE SUN.

Melanin absorbs UV radiation from the sun and can protect your skin from UV damage. (That’s why people of color, who have more melanin, get fewer sunburns.) When your skin gets sun damage, your body assumes that’s just how it is now, that you’ll always be pelted with UV radiation, so it creates more melanin to compensate and protect your skin. (That’s why you get darker when you tan.)

This can make PIH exponentially worse – I mean, if you’re trying to heal PIH, you don’t want to do anything that will make even more melanin. Wear sunscreen EVERY DAY, especially if you’re trying to fade PIH. It doesn’t matter if you don’t burn, you still need to wear sunscreen. EVERY DAY.

Another common mechanism has to do with tyrosinase, an enzyme that facilitates melanin production. Many PIH-fighting ingredients work by inhibiting tyrosinase, so your skin can’t produce as much new melanin.

Common Tyrosinase Inhibitors


When you think “skin bleaching”, this is the ingredient you’re thinking of. It’s a very powerful tyrosinase inhibitor that can also cause cell death of melanocytes, or melanin-producing skin cells. It can have some very serious side effects. Only use this under recommendation and supervision of a dermatologist. It’s typically used in concentrations of 2-4%, but your derm can prescribe up to 10% formulations.


A safer derivative of hydroquinone, arbutin has the same tyrosinase-inhibiting effects without causing cell death. Unlike most of the ingredients listed here, arbutin is actually much more effective on light skin tones than on dark ones. One thing to be wary of: in too high doses, arbutin can actually cause postinflammatory hyperpigmentation. Yikes.

Product ideas with arbutin: Hada Labo Shirojyun Arbutin Lotion (there’s also a thicker, more moisturing milk); Graymelin Propolis 80 Energy Ampoule

Kojic Acid

In studies of PIH-lightening abilities, kojic acid is the standard that everything is measured against. It’s extremely effective, but potentially very irritating, and should be used in concentrations of 1-4%.

I’ve never used kojic acid, and it’s powerful stuff, so I don’t feel comfortable recommending any products. Ask your dermatologist if you want to start using it.

Azelaic Acid

Another super-great tyrosinase inhibitor, azelaic acid also kills off abnormal melanocytes. It generally causes less irritation and fewer side effects than similarly powerful ingredients like hydroquinone and retinoids. It’s also the love of Snow White and the Asian Pear’s life. (Well, one of them.)

Product ideas with azelaic acid: Curology, a subscription service that gets you a customized prescription cream plus unlimited consultations with a medical skincare professional (use that affiliate link to get your first month free)

Licorice Root Extract

This is an ingredient that has been used in traditional skin care for thousands of years, and has a scientifically-proven ability to inhibit tyrosinase. It’s a great, gentle way to lighten PIH and brighten your overall skin tone.

Product ideas with licorice root extract: It’s Skin Power 10 Formula LI Effector, Sulwhasoo Snowise EX Whitening Serum

Vitamin C

This much-loved ingredient is also a tyrosinase inhibitor. All forms of vitamin C (including L-Ascorbic Acid and Magnesium/Sodium Ascorbyl Phosphate) will fade PIH. L-Ascorbic Acid is also an exfoliant and antioxidant, while MAP/SAP are much more stable and less likely to cause irritation.

Product ideas with vitamin C: Curology (again), OST C21.5, Skinceuticals CE Ferulic

N-Acetyl Glucosamine

Rounding out our list of tyrosinase inhibitors is NAG. This ingredient is best used at concentrations of 2% and works synergistically with niacinamide to make both ingredients work better.

Product ideas with N-acetyl glucosamine: my bae Dr. Jart+ Premium Firming Sleeping Mask, Holy Snails’ Shark Sauce (only available through Facebook co-op group)

Other ingredients to treat PIH

There are a number of other mechanisms to fade PIH besides inhibiting tyrosinase. Here are some of those players.


God, what can’t retinoids do? PIH-wise, they cause increased cell turnover, meaning you’re getting rid of the abnormal melanocytes faster. Plus, retinoids can have anti-inflammatory effects, which can help prevent future postinflammatory hyperpigmentation. Tretinoin is the best retinoid for PIH, but it can be very irritating, so start with a low percentage and work your way up.

Product ideas with retinoids: Tretinoin is prescription-only, but you can get it through Curology


Alpha-hydroxy acids also increase cell turnover, plus they disperse melanin in the basal layer of the epidermis. They have a lot of other great properties, too.

Product ideas with AHAs: Cosrx AHA 7 Whitehead Power Liquid, Silk Naturals 8% AHA Toner


Niacinamide, in addition to its many magical qualities, interrupts the transfer of melanin between skin cells. It might also decrease melanogenesis, or the production of melanin. It’s best in concentrations of 2-5% and is one of my all-time favorite ingredients – and one of the most thoroughly scientifically studied and reviewed cosmetic ingredients. Combine it with N-acetyl glucosamine to kick both ingredients into the stratosphere.

Product ideas with niacinamide: Cerave PM, Cosrx Galactomyces 95 Whitening Power Essence, Curology (last time, I promise!)


Like niacinamide, soy proteins inhibit melanin transfer between cells. I’ve been using a lot of soy products recently and I think it’s my new favorite ingredient.

Product ideas with soy: These are the products that have made me fall in love with soy recently: I Love Sasatinnie Soy Milk Mask, Sana Soy Milk Astaxanthin Lifting Gel, Sana Nameraka Isoflavone Wrinkle Eye Cream

I think I have PIE, not PIH. What do I do?

Uh, wait for more research to come out, I guess. Like I mentioned above, one study indicated pulsed dye laser treatment was effective at treating PIE. Unfortunately, none of the ingredients listed in this post will do anything for PIE, since all these ingredients affect melanin, and PIE is melanin-free. It will fade on its own over time, but there’s not much we know in terms of treatment.

Your best bet is to avoid PIE in the first place, by both treating your acne so you get as few lesions as possible, and reducing inflammation so the subsequent PIE isn’t as bad. Try using tretinoin or a BHA, both of which fight acne and reduce inflammation. DON’T PICK! Picking, squeezing, or otherwise being rough with your acne will trigger a bigger inflammatory response, which will make the subsequent PIE worse. Other than that, concealer is your friend.

In other news, I’ve been researching this article for so long that I don’t even know what to do with myself now that it’s written. Time to start drinking, I guess?

Sources: 1, 2, 3, 4, 5, 6


  1. Hey, how did you know I was picking? 😛 Anyway, this is a really great go-to summary, thanks! As for kojic acid, I recently started using the popular Kojie San soap about 2x weekly. More drying than Likas Papaya soap for sure. In any case, it seems there are other, equally effective ingredients though (especially if “stacked” in a routine) without the consequence of drying and irritating.

    1. Haha, I’m psychic 🙂 Yeah, if there’s anything I gathered from my research, it’s that there are a LOT of ways to fade PIH, so if kojic acid is too harsh, you can easily switch to something gentler like azelaic acid.

  2. I have so much PIE! And not the kind I love to eat. Sob! Shark Sauce helped mine fade, but the spots are still there. I have spots from years ago…can’t even remember the pimple but the spot has been there forever. I’m hoping more research is done on PIE. –Angela

    1. I know the feeling! I have what I call my “Mizon constellations” – Mizon broke me out in two clusters of terrible, super-inflamed acne, and I still have the PIE from it 🙁

  3. Is find that vitamin C is great for reducing fresh PIE and reducing marks left from fresh acne. I use the Ordinary 23% AA as a spot treatment for acne and it works for me.

  4. Hey Acid Queen, just want you to know that even now, years later, you having moved on from a mythical reddit diy legend to a thriving skincare queen…your posts are so helpful and I reference them often when I’m on the hunt for new lotions n potions (or trying to figure out why current one aren’t working). For that, I thank you. You have made a lasting, invaluable contribution to our little niche in this big, big world.

Leave a Reply