Once an inflammatory acne lesion subsides, it frequently leaves behind persistent marks that can endure for months. Clinically, these marks fall into two distinct pathophysiological categories: Post-Inflammatory Hyperpigmentation (PIH) and Post-Inflammatory Erythema (PIE). Correctly diagnosing the lesion type is crucial for selecting effective treatment.
The Glass Slide Test (Diascopy)
The most straightforward clinical method to differentiate between PIH and PIE is diascopy. Press a clear glass slide firmly against the discolored mark:
- If the mark blanches (temporarily disappears): It is PIE, caused by dilated or damaged microvascular capillaries.
- If the mark remains visible: It is PIH, caused by excess melanin deposited in the epidermis or dermis.
Targeted Active Ingredients by Mark Type
| Condition | Underlying Pathology | First-Line Actives |
|---|---|---|
| PIE (Red / Purple) | Erythematous capillary damage | Tranexamic Acid, Azelaic Acid, Centella Asiatica, Pulsed Dye Laser (PDL) |
| PIH (Brown / Dark) | Overactive melanocytes & melanin pool | Alpha Arbutin, Kojic Acid, Niacinamide, Retinoids, Glycolic Acid |