PIE vs PIH after Accutane: telling them apart

PIE is red because it is blood vessels. PIH is brown because it is pigment. Both are flat marks left where acne healed, neither is a scar, and both fade with sun protection and time, but on different timelines and with different treatment options. Colour tells you which one you are looking at in about two seconds, and pressing the mark confirms it.

Getting this right matters more than it sounds, because the products aimed at one do essentially nothing for the other. The distinction is a formal one in the dermatology literature: a 2013 review that helped popularise the term PIE describes it as residual erythema, explicitly distinct from PIH, which describes subsequent pigment change. Both tend to resolve over time.

At a glance

How do I tell if I have PIE or PIH?

Two checks, in order.

Colour first. Red, pink, or purple points to PIE. Brown, tan, or grey points to PIH. This gets you the right answer most of the time on its own.

Then press the mark. Use a fingertip, or the edge of a clear glass pressed flat against the skin, which is easier to watch. Press firmly for a second, then release. PIE usually blanches: the colour drains briefly and floods back, because you are temporarily pushing blood out of the dilated vessels that make the mark. PIH does not blanch, because pigment sitting in the skin does not move when you press on it.

It is not a perfect test. Marks can be ambiguous, some are brownish-red, and lighting changes what you see. But between colour and blanching you can usually place a mark correctly without a clinic visit.

PIE, in short

Post-inflammatory erythema is the vascular mark. When a pimple inflames, blood vessels near the surface dilate to supply the inflammatory response, and after the spot heals those vessels can stay dilated for months. What you see is the blood in them.

Because it is vascular, PIE behaves in ways pigment does not. It often looks worse straight after heat, exercise, or a hot shower, when blood flow increases. That flush is temporary and not the mark worsening.

Full detail, including why it fades the way it does, is in the red marks after Accutane guide.

PIH, in short

Post-inflammatory hyperpigmentation is the pigment mark. Inflammation triggers melanocytes to produce extra melanin, and that pigment is deposited and left behind after the spot itself resolves. What you see is the melanin.

Because it is pigment, PIH clears only as the skin renews and carries the excess melanin away, which is slower than vessels normalising. That is the main reason its timeline runs longer.

Full detail is in the dark spots after Accutane guide.

Why is PIH so hard to get rid of?

Depth, mostly, and it is the part almost nobody explains.

Pigment does not all sit at the same level. It can be deposited in the upper layer of the skin, deeper in the dermis, or in both at once. Surface pigment clears comparatively readily as the skin turns over. Deeper pigment is much slower, because there is simply more skin renewal required to carry it away, and it is less reachable by anything applied topically.

This is why two people with apparently similar brown marks can have completely different timelines, and why marks that have been present for a year or more tend to be the stubborn ones. It also reframes the usual conclusion: a mark that has not shifted in months is more often deep pigment behaving normally than a product that failed.

PIE has no equivalent complication. Vessels are where they are, and they normalise or they do not.

Why the distinction actually matters

If the two faded the same way and responded to the same things, this would be trivia. They do not.

The treatment mismatch is the expensive part. Brightening and pigment-fading products act on melanin. PIE contains no excess melanin, so applying them to red marks does nothing. This is the most common wasted effort in post-acne skincare, and the usual conclusion drawn from it, that nothing works, is wrong. The mechanism was mismatched.

The reverse applies too. Vascular treatments target dilated vessels and have nothing to act on in a brown pigment mark.

The timelines differ enough to change expectations. Someone with PIH judging progress against a 3-month expectation borrowed from PIE will conclude something is wrong when their marks are behaving exactly as expected.

What they share: daily broad-spectrum sun protection and time help both, and UV works against both. Skin also stays more sun-sensitive for months after Accutane, which makes consistent SPF the one habit worth holding regardless of which mark you have.

Beyond that, the useful options diverge, and both are conversations to have with the dermatologist who supervised your course rather than steps to rush into. Timing matters too: skin stays more reactive for a period after isotretinoin, which is worth raising before any procedure.

Which one are you more likely to have?

Skin tone shifts the odds considerably.

Melanin-rich skin produces more pigment in response to any inflammation, so medium to deeper skin tones (Fitzpatrick IV to VI) more often show PIH, it tends to be darker, and it tends to persist longer. Lighter skin tones (Fitzpatrick I to II) more often show PIE, because redness reads more visibly and the pigment response is milder.

This is a tendency, not a rule, and many people have both at once: a red mark from one spot and a brown mark from another, sometimes on the same cheek. That is normal and it is a large part of why the two terms get confused.

What about melasma?

There is a third brown thing, and it is the one most likely to be mistaken for PIH. Melasma is also hyperpigmentation, but it is not post-inflammatory: it is driven by hormones, UV, and heat rather than by a healed spot.

Two features separate it from PIH quickly. Shape: PIH is a scattering of discrete marks, each sitting where a specific pimple was, while melasma forms larger connected patches. Symmetry: melasma is roughly mirrored on both sides of the face, usually cheeks, forehead, upper lip, or chin, in a pattern that has nothing to do with where acne appeared.

The reason it matters is the timeline. PIH fades. Melasma is chronic and relapsing, and applying the PIH expectation to it means waiting a year or more for something that may not clear unassisted. The dark spots guide covers the full differential, including why post-Accutane photosensitivity can trigger it and why melasma is easier to worsen with aggressive treatment than PIH is.

When it is neither

Both PIE and PIH are completely flat. That single fact rules out the third category people worry about.

Run a finger over the mark. If you feel a depression, a pit, or a raised ridge, that is textural change, which means scarring rather than a post-inflammatory mark. Scarring does not fade on the timelines above and is a different conversation with a dermatologist. The skin texture guide covers how to tell early textural change from a recovering barrier.

A few other patterns fall outside both:

• A mark changing in size or shape over weeks. Both PIE and PIH fade rather than grow or shift.
• Redness spreading beyond where the old spots were, rather than sitting in them.
• Symmetric brown patches on both cheeks or across the forehead, which point toward melasma rather than PIH.
• New inflammatory bumps mixed in with the marks, which raises a different question entirely, covered in whether acne is coming back.

These are orientation signals rather than diagnoses. Anything that does not behave like a flat, slowly-fading mark is what a dermatologist is for.

When to see your dermatologist

Most flat marks of either kind resolve with sun protection and time and do not need an appointment. Reasons to check in:

• A mark that is raised or textured rather than flat.
• A mark that has not changed at all after a year of consistent sun protection.
• A mark changing in size, shape, or colour rather than gradually lightening.
• Marks bothering you enough that you are considering treatment. That is a legitimate reason on its own, and the right options depend on which mark it is and on your skin tone, which is exactly the conversation to have in person.

Isotretinoin guidance from the British Association of Dermatologists and the American Academy of Dermatology both note that skin stays more reactive for a period after treatment, which is worth mentioning if you are discussing any procedure. For where marks sit in the wider recovery, the post-Accutane recovery guide has the whole arc.

Tracking marks over time

Fading marks are the single hardest thing to judge in a mirror. The week-to-week change is below what you can perceive, and memory quietly overwrites the starting point, so the honest experience is that marks feel stuck even while they are clearing.

A dated photo in consistent light, compared over a couple of months rather than checked each morning, is the only reliable way to know. Aftertane was built for that longer read: a private timeline of dated photos and severity readings that turns "I think this is never going away" into something you can actually check. Free to use, and a phone album with a monthly reminder does the same job.