What is post-inflammatory hyperpigmentation (PIH)?
Post-inflammatory hyperpigmentation is a flat dark mark left after acne, a rash, an injury or skin irritation. Inflammation triggers extra melanin, the pigment that gives skin its colour. PIH can affect any skin tone, but is often more noticeable and persistent in darker skin.
PIH is one cause of dark spots. A brown mark is not automatically PIH, and colour alone cannot tell you its cause, depth or best treatment.
Are acne marks the same as acne scars?
| Concern | Typical appearance | What it means |
|---|---|---|
| PIH | Flat brown or grey-brown marks | Extra pigment after inflammation |
| Post-inflammatory erythema (PIE) | Flat pink, red or purplish marks | Blood-vessel changes after inflammation; may coexist with PIH |
| Acne scars | Indentations or raised areas | A change in skin texture; fading pigment does not remove the scar |
If you are unsure which you have, a skin examination is more useful than choosing treatment from the colour of a photograph.
How long does PIH take to fade?
Many marks gradually fade once the inflammation has settled, but this often takes months. Deeper pigment may last much longer. There is no reliable four-week deadline, and slow fading does not automatically mean you need laser treatment.
New acne, scratching, irritating products and sun exposure can keep the cycle going. Controlling the trigger matters as much as treating the existing marks.
Daily care for PIH in Thailand
- Address ongoing inflammation. Avoid picking or squeezing acne. If your skin is still itchy, sore or irritated, deal with the inflamed skin and its triggers before adding more brightening products.
- Use sunscreen consistently. Choose a broad-spectrum, water-resistant sunscreen with SPF 30 or higher, plus shade, a hat and protective clothing. Reapply about every two hours outdoors and after swimming or sweating, following the label. This matters during everyday outdoor activities as well as beach trips.
- Keep the routine gentle. Use a mild cleanser and a moisturiser your skin tolerates. Introduce one new product at a time, following its directions. Scrubbing, strong home peels and layering several active ingredients can cause more irritation.
A tinted sunscreen containing iron oxides can add protection against visible light. Stop a new cosmetic if it causes burning, itching or a rash, and seek advice if symptoms persist. Ask your prescriber before changing a prescribed treatment.
Can creams help, or do you need a procedure?
Topical treatment may help PIH fade. A clinician may consider azelaic acid or a retinoid medicine, depending on the marks, ongoing acne and your skin’s tolerance. Clinical studies support particular formulations; they do not prove that every serum works equally well. Irritation can worsen pigmentation, so stronger is not necessarily better.
Cosmetic retinol and prescription retinoids are not interchangeable. Tell the clinician if you are pregnant, trying to conceive or breastfeeding before choosing treatment. Avoid retinoids, including retinol, during pregnancy. Retinoid medicines should also be avoided when planning pregnancy.
Peels or lasers may be considered for selected cases, but they can cause further darkening, lighter patches or scarring. Choice depends on the diagnosis, skin tone and previous reactions, rather than how dark the mark looks. Our pigmentation treatment comparison explains the main options and limitations.
Before a procedure, ask about likely improvement, total cost and recovery. Get specific instructions for sunscreen, makeup and restarting skincare, especially if the skin will be broken. There is no single session count or downtime estimate that fits every treatment.
When should a dark mark be checked?
Arrange a prompt skin assessment if a spot is new without a clear cause, looks different from your other marks, grows, changes colour or shape, itches or bleeds. Do not try to fade or laser an unexplained spot before it is examined.
You can also seek advice whenever acne keeps leaving new marks, skincare makes them worse, or gradual fading is not meeting your expectations. For help planning care for post-acne marks, you can consult a clinician at Smooth Clinic.
References
- American Academy of Dermatology. How to fade dark spots in darker skin tones; Acne scars: Overview.
- Shucheng H, et al. Effects of 15% azelaic acid gel on post-inflammatory erythema and hyperpigmentation in acne. Dermatology and Therapy. 2024.
- Bulengo-Ransby SM, et al. Topical tretinoin for post-inflammatory hyperpigmentation. New England Journal of Medicine. 1993.
- American Academy of Dermatology. Pregnancy skin care; Chemical peels: FAQs; Warning signs of melanoma.
- UK Medicines and Healthcare products Regulatory Agency. Retinoid medicines and pregnancy precautions, including topical retinoids when planning pregnancy. 2019.
- American Academy of Dermatology. How to apply sunscreen; 10 tips for clearing acne in darker skin tones; Skin conditions that lasers can treat.
- Ho SGY, et al. Topical and laser treatment for acne-related PIH: a retrospective study. Lasers in Surgery and Medicine. 2011.