Post-inflammatory hyperpigmentation (PIH) is a common pigment change that can develop after skin inflammation or injury. It appears as flat areas of discolouration that may remain after the visible inflammation has improved.
PIH itself is not an active infection, an active acne lesion or a true scar. It is a pigment response caused by increased melanin production following inflammation.
How PIH Forms
PIH develops when inflammation or skin injury sends signals that stimulate melanocytes, the cells responsible for producing melanin. Common triggers include:
- inflammatory acne lesions
- eczema or dermatitis
- irritation from skincare products
- allergic or irritant skin reactions
- cuts, burns or other physical trauma
- repeated picking, friction or rubbing
- irritating cosmetic treatments or procedures
Inflammatory signals can increase melanin production and the transfer of melanin to surrounding epidermal cells. If deeper inflammation damages the basal layer of the epidermis, some melanin may also enter the dermis.
These processes can leave flat areas of discolouration after the original inflammation has settled. The colour and persistence of PIH depend partly on the depth of the pigment and the severity and duration of the inflammation.
Why PIH and Active Acne Can Appear Together
PIH does not always appear only after acne has completely resolved. New inflammatory lesions, healing lesions and pigmentation from earlier breakouts can exist at the same time.
Many clients therefore have active acne and older PIH together. While new inflammation is developing, pigment from previous lesions may still be visible.
Several stages may appear together:
- new inflamed acne lesions
- healing acne lesions
- flat brown or grey-brown PIH from earlier breakouts
When new lesions continue to form before older marks have faded, the skin may appear unchanged even though some areas are recovering.
Managing acne-associated PIH therefore requires more than brightening products. The priorities include controlling active inflammation, reducing new breakouts, avoiding picking and irritation, supporting the skin barrier and using consistent broad-spectrum sun protection.
The goal is not only to fade existing marks but also to prevent repeated inflammation from producing new PIH.
Why UV and Inflammation Can Worsen PIH
PIH can become darker or persist longer when melanocytes continue to be stimulated by light exposure or ongoing inflammation. Factors that may worsen PIH include:
- UVA and UVB exposure
- visible-light exposure, particularly in medium-to-deep skin tones
- ongoing inflammatory acne, eczema or dermatitis
- repeated picking, rubbing or friction
- irritation from strong skincare products or procedures
- skin-barrier damage accompanied by continued inflammation
UV exposure can stimulate melanocyte activity and darken existing marks, even after the original acne lesion or irritation has improved. Repeated irritation may also create new inflammation and trigger additional pigment production.
For this reason, managing PIH requires both inflammation control and consistent sun protection. Gentle skincare, avoiding unnecessary irritation and using daily broad-spectrum sunscreen can help prevent existing marks from becoming darker or more persistent.
Types of PIH (Clinical Classification)
PIH is commonly classified according to where excess melanin is located within the skin: the epidermis, the dermis or both layers.
1. Epidermal PIH
- excess melanin is concentrated within the epidermis
- commonly appears tan, light brown, brown or dark brown
- usually fades more readily over time
- tends to respond better to topical treatment
2. Dermal PIH
- pigment has entered the dermis and is taken up by macrophages, forming melanophages
- may appear grey-brown, blue-grey or slate-grey
- generally fades more slowly
- responds less predictably to topical treatment
3. Mixed PIH
- pigment is present within both the epidermis and dermis
- may contain a combination of brown and grey or blue-grey tones
- improvement varies according to the depth and persistence of the pigment
The visible colour may provide clues about pigment depth, but appearance alone cannot always confirm the classification. Persistent, changing or unclear pigmentation should be assessed by a physician or dermatologist.
PIH Is Different From Post-Inflammatory Hypopigmentation
Not every colour change following inflammation is PIH. PIH involves increased pigment and produces darker marks. Post-inflammatory hypopigmentation is a separate condition that produces lighter patches.
- PIH: increased melanin or uneven melanin distribution → darker marks
- Post-inflammatory hypopigmentation: reduced or disrupted pigmentation → lighter patches
Post-inflammatory hypopigmentation may develop when inflammation or injury temporarily disrupts melanocyte activity, melanin production or pigment transfer. It can follow dermatitis, skin injury or an irritating cosmetic treatment.
In my 18 years of clinical practice, I have encountered post-inflammatory hypopigmentation much less frequently than PIH. However, this is a practice-based observation and does not determine how common the condition is in the general population.
Lighter patches can also have causes unrelated to previous inflammation. Persistent, spreading or unexplained areas of lighter skin should be assessed by a physician or dermatologist.
Clinical Insight
PIH does not behave the same way in every client. Its severity, colour and duration may be influenced by:
- the intensity and duration of the original inflammation
- the depth of the pigment
- skin tone and melanocyte responsiveness
- ongoing acne, eczema or dermatitis
- UV and visible-light exposure
- picking, rubbing or repeated irritation
- skin-barrier condition and treatment tolerance
In clinical practice, I do not evaluate a dark mark only by its colour. I also consider whether active acne or irritation is still present, whether the skin barrier is stable and whether the current skincare routine is creating additional inflammation.
Two clients with similar acne may develop very different pigmentation. Using strong pigment-focused treatments before controlling active inflammation or irritation may make PIH darker or more persistent.
Key Takeaway
Post-inflammatory hyperpigmentation is a flat pigment change that develops after inflammation or skin injury. It is not an active infection, an active acne lesion or a true scar.
PIH may be epidermal, dermal or mixed. The depth of the pigment, intensity of the original inflammation, skin tone, light exposure and continued irritation can influence its colour and persistence.
Effective management begins by controlling the cause of inflammation, preventing new irritation, supporting the skin barrier and using consistent broad-spectrum sun protection. Pigment-focused treatment can then be introduced according to the skin’s condition and tolerance.
Stronger or more frequent brightening treatments do not always produce faster improvement. If a product or procedure creates new inflammation, it may darken existing PIH or trigger additional pigmentation.
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Angelina
Medical Esthetician (18 years of experience)
Skin Logic by Angelina
