The pimple is gone, but the dark mark it left behind is still there weeks later. That mark is post-inflammatory hyperpigmentation, or PIH. It's not a scar, and with the right care, it fades.
What is post-inflammatory hyperpigmentation?
When skin is inflamed or injured, it can respond by producing extra melanin in that spot. The result is a flat mark that can be pink, red, brown, or nearly black, depending on your skin tone. Post-inflammatory pigmentation is especially common in medium to deep skin tones, where pigment cells are more reactive.
Common causes
- Acne breakouts, especially when picked or squeezed
- Ingrown hairs after shaving or waxing
- Razor burn and friction
- Bug bites, scratches, and minor burns
- Eczema flares and allergic reactions
- Overly aggressive treatments, peels, or scrubs
PIH in the bikini area and underarms
Many people notice dark marks along the bikini line or underarms and assume it's their natural skin tone. Often it's PIH from repeated shaving, ingrown hairs, and friction. Switching from shaving to regular waxing or sugaring, and exfoliating gently between appointments, often helps these areas even out over time. Our Brazilian wax aftercare covers how to prevent ingrown hairs, and our guide to dark underarms and bikini line goes deeper.
How to prevent PIH
- Don't pick. Picking and squeezing deepen inflammation and make marks darker and longer-lasting.
- Treat inflammation early. Calm breakouts and irritation quickly with gentle, non-stripping products.
- Exfoliate to prevent ingrown hairs, two to three times a week, gently.
- Wear sunscreen daily. UV exposure darkens fresh marks and makes them last longer.
How to fade post-inflammatory hyperpigmentation
- Sunscreen first. A broad-spectrum SPF 30+ every day. See our guide to sunblock for pigmentation.
- Azelaic acid: fades marks and treats the breakouts that cause them.
- Niacinamide and vitamin C: gentle brighteners for daily use.
- Retinoids: speed up turnover, but introduce slowly. Irritation creates new PIH.
- Gentle exfoliating acids like mandelic or lactic acid.
Avoid harsh scrubs and anything that leaves your skin stinging or red. With PIH, gentle is faster.
How long does PIH last?
Surface-level marks often fade within three to six months with good care. Deeper marks can take longer. Without sun protection, PIH can linger for a year or more.
PIH vs. acne scars
PIH is flat; only the color has changed. Acne scars change the texture of the skin, leaving indents or raised areas. If you can feel it, it's likely a scar and needs a different approach. Learn more about the other types of discoloration in our hyperpigmentation guide.