# Red Mark or Brown Mark: The Glass Test That Decides Your Acne Mark Treatment

Source: https://clearskinbrief.com/blog/2026-11-10-acne-marks-pih-pie-glass-test.html

The pimple is gone and the mark is still there, flat and red, exactly where the lesion was. Or flat and brown. People call both of them scars, treat both of them the same way, and wonder why nothing works. They are not the same thing. One is blood in vessels. The other is melanin in skin. A clear glass tells them apart in a minute, and the treatment follows from the answer.

## Three leftovers, three structures

Inflammatory acne leaves three different things behind, and they involve three different structures. Post-inflammatory hyperpigmentation is excess melanin: brown, tan, or dark brown flat marks where the inflammation told melanocytes to overproduce. Post-inflammatory erythema is dilated capillaries: flat red, pink, or purplish marks where the vessels built to fight the blocked follicle never demobilised. True acne scars are structural: a change in collagen during healing that leaves a depression or a raised area you can feel. The AAD notes that inflammatory acne can leave dark spots as well as permanent scars, and the risk of scarring rises with deeper inflammatory acne, particularly nodules and cysts. PIH and PIE are not scars. The skin texture stays normal. That distinction matters because pigment treatments, vascular treatments, and structural treatments do different jobs, and using one on the wrong structure fails twice: the mark stays, and the treatment can make it worse. Hydroquinone on a vascular red mark achieves no clearance. Aggressive ablative laser resurfacing on vascular erythema can worsen the inflammation.

PIH is most prominent in Fitzpatrick skin types IV to VI, where melanocytes are more reactive. PIE is most prominent in types I to III, where fair skin shows the vessels. A lesion on South Asian skin often starts as vascular redness that stimulates melanocytes to deposit dark pigment over the following weeks, so the same spot can be PIE first and PIH second. That sequence is why a mark can change colour while you watch it, and why the treatment has to change with it.

## The glass test

Press the mark with a clear glass and watch. PIE blanches: the redness empties out under pressure and refills when you release, because it is blood in vessels and pressure pushes the blood out. Brown PIH stays exactly as brown, because melanin does not move. A mark you can feel as a dip or a bump is structural, and no amount of pressing changes it. The test costs nothing and settles the question that decides the whole treatment plan. It is the same test dermatologists use in clinic, called diascopy, and it works at home because the physics is the same: blood moves, pigment does not.

Most untreated PIE resolves on its own within roughly 3 to 6 months as the vessels remodel. PIH takes longer, typically 3 to 6 months for the pigment to shed through complete cellular turnover, and sometimes up to 24 months. Both timelines assume the acne itself is controlled and the skin is not being picked at, because every new lesion restarts the clock and every picked lesion adds a new mark. The fastest way to fade either mark is to stop making new ones.

## What actually works, by mark

For PIE, vessels answer to vascular treatment. Pulsed dye laser is the dermatology consensus first line for rapid clearance: light absorbed by haemoglobin closes the lingering capillaries, the same physics as facial thread vein work, delivered gently across a field of marks. Intense pulsed light has trial support too. For topicals, azelaic acid is the primary evidence backed option, and niacinamide supports the barrier while the vessels settle. What does not work on PIE is the brightening shelf: vitamin C, hydroquinone, and aggressive exfoliation act on pigment, and PIE contains none. For PIH, the plan is pigment directed: daily sun protection first, because UV drives more melanin into the mark, then tyrosinase inhibitors like hydroquinone, azelaic acid, and vitamin C, plus retinoids and AHAs to speed turnover. For true atrophic scars, ice pick, boxcar, and rolling depressions need collagen work: subcision, radiofrequency microneedling, TCA CROSS, or fractional laser. Colour correcting products and serums cannot fix a dip. The AAD's emphasis is on early and effective acne treatment as the way to reduce scarring risk in the first place, which is the least glamorous and most effective advice in the whole field: treat the acne, and there are fewer marks to sort out afterward.

Keep reading: [Pimple Patches: What Hydrocolloid Actually Does, and When It Does Nothing](2026-11-09-pimple-patches-hydrocolloid-what-it-does.md), [The Retinol Sandwich: Buffering Works, but It Changes the Dose](2026-11-08-retinol-sandwich-method-buffering-dose.md), [Niacinamide 2% vs 10%: the concentration that stops helping](2026-11-06-niacinamide-2-vs-10-percent-concentration.md).

## Frequently asked questions

### How can I tell if my acne mark is PIE or PIH?

Press it with a clear glass. PIE blanches, the redness empties out under pressure and refills when you release, because it is blood in vessels. Brown PIH stays exactly as brown, because melanin does not move. A mark you can feel as a dip or a bump is neither: it is a true acne scar, which is structural.

### How long do red acne marks take to fade?

Most untreated PIE resolves on its own within roughly 3 to 6 months. PIH takes longer, typically 3 to 6 months for the pigment to shed through cellular turnover, and sometimes up to 24 months. True atrophic scars do not fade on their own and need a structural treatment.

### Will vitamin C or niacinamide fade a red acne mark?

Not directly. Brightening serums act on pigment, and a red PIE mark is blood in vessels, not melanin. Vitamin C and niacinamide help PIH, the brown mark, and niacinamide supports the barrier while PIE heals, but neither closes a dilated capillary. That is why red marks treated with brightening serums are the most mis-shopped marks in skincare.

### What is the first line treatment for PIE?

Pulsed dye laser is the dermatology consensus first line for rapid clearance, because the light is absorbed by haemoglobin and closes the lingering capillaries. For topicals, azelaic acid is the best supported option. Daily broad spectrum SPF 30 or higher is the baseline for every mark, because sun exposure over inflamed micro vessels drives secondary melanin production.