Understanding Post-Inflammatory Hyperpigmentation (PIH)

PIH is darker pigmentation at the site of previous inflammation or injury. Understanding that event helps distinguish these marks from other pigmentary conditions.

Inflammation and melanin production

Acne, eczema, an infection or an injury can trigger PIH. Inflammation stimulates the cells that make melanin. This pigment can remain in the epidermis or reach the dermis when the skin’s basal layer is damaged. Some procedures can also worsen pigmentation by causing further irritation or skin injury.

Types of hyperpigmentation: superficial or deep

Pigmentation can lie in the surface or deeper layers of the skin:

• Epidermal PIH: Pigment builds up in the epidermis, the surface layer of the skin. The spots are often brown. Some treatments applied to the skin may reduce them, with a variable response.
• Dermal PIH: Pigment lies deeper in the dermis, where immune cells can take it up. Marks may look greyish or purplish brown and take longer to fade.

Role of UV and aggravating factors

UV rays can darken PIH marks. Sun protection is therefore part of care. Other forms of skin damage can also cause the spots to persist:

• Picking at lesions: Scratching, puncturing or squeezing an acne pimple increases the risk of spots and scars.
• Using irritating products: A cosmetic or skin-care product that irritates the skin can cause new, darker marks.
• Repeated friction: When it irritates or injures the skin, hyperpigmentation can follow.

Influence of skin type

PIH can affect every skin colour. However, it is more common in darker skin, where marks can be more intense and last longer. Skin colour alone cannot predict how long a spot will last or determine a treatment protocol.

Before treating a spot as PIH, an examination helps identify its cause and distinguish it from other pigmented lesions.

Differential diagnosis

Other conditions can cause pigmented lesions, including:

• Melasma: Spots that develop mainly on the face, sometimes during pregnancy or while taking certain contraceptives. Hormones are among the possible factors, along with sun exposure.
• Solar lentigo: A brown spot that appears on an area often exposed to the sun.
• Seborrhoeic keratosis: A benign skin growth, often brown, that becomes more common with age. It can resemble other lesions and sometimes needs to be examined.
• Naevus (mole).

Diagnosis is based on the spot’s history and a skin examination. A biopsy, which takes a small sample of skin, may sometimes be needed to clarify the diagnosis.

PIH assessment

During the assessment, the doctor may consider the following:

• Medical history: When the spots appeared, previous acne or eczema, injuries, products used and sun exposure provide useful information. Previous episodes of pigmentation are also part of the history to report.
• Clinical examination: The doctor examines the location and appearance of the spots, including their colour, size and shape.
• Depth assessment: A Wood's lamp (which emits special ultraviolet light) may help determine whether pigmentation is superficial (epidermal), as it will appear clearer under this light, or deep (dermal), as its appearance will not change.

The choice of treatment depends in part on the cause of inflammation, the depth of the pigment and skin tolerance. Advice from a dermatologist can help clarify these factors and the available options.

Lightening creams and lotions (topical agents)

Some treatments applied to the skin can reduce surface spots. Their effect varies, and irritation can worsen pigmentation. Choosing a product therefore requires considering what caused the marks and what the skin tolerates.

• Hydroquinone: This is the most powerful lightening agent, but it must be used cautiously because of irritation risk and a reverse effect in which skin becomes darker (a phenomenon called ochronosis).
• Retinoids: They promote skin-cell turnover and pigment elimination.
• Azelaic acid: It has properties that calm inflammation and lighten skin.
• Kojic acid: It slows melanin production.
• Vitamin C: An antioxidant that brightens the complexion and protects against cellular damage.
• Niacinamide: It reduces inflammation and hyperpigmentation.

Dermatological procedures

Several dermatological procedures can treat PIH, particularly when topical treatments are insufficient:

• Chemical peels: This technique applies an acid solution to skin to remove superficial layers (exfoliate) and encourage cell turnover. Glycolic acid, salicylic acid or trichloroacetic acid (TCA) peels may be used.
• Microdermabrasion: This technique “sands” the superficial skin layer with a specific device to exfoliate it.
• Lasers: Different laser types can target melanin pigment, such as Q-switched lasers, fractional lasers or pulsed dye lasers. Laser selection depends on skin type and pigmentation depth.
• Microneedling: This technique uses a device fitted with microneedles to create tiny skin punctures. This stimulates collagen production and helps lightening products penetrate skin better.

Important precautions and considerations

Precautions are part of care, whatever treatment is being considered:

• Sun protection: Daily application of broad-spectrum sunscreen with SPF 30 or higher supports treatment on exposed areas. Tinted sunscreen containing iron oxides also protects against visible light.
• Avoiding irritation: Gentle, well-tolerated products limit skin damage that could create new spots.
• Adapting treatment to the skin: Irritation caused by a treatment can worsen PIH. Tolerance and a history of pigmentation need particular attention; no single concentration is suitable for all darker skin tones.

Prevention aims to limit new inflammation and factors that darken spots:

• Sun protection: Broad-spectrum sunscreen with SPF 30 or higher is applied daily to exposed skin, even on cloudy days. Outdoors, it is reapplied every two hours and after swimming or sweating.
• Avoiding picking at lesions: Scratching, puncturing or squeezing acne pimples increases the risk of marks and scars.
• Using gentle products: Non-irritating products, including fragrance-free options, may be better suited to skin prone to spots. A product that burns or stings must be stopped and its use reassessed.
• Managing inflammation: Acne or eczema that keeps flare-ups occurring must also be treated. Fading a spot without addressing its cause does not prevent new marks from appearing.
• History of pigmentation: PIH that appeared after a treatment or procedure should be reported before another procedure. The risks and other options should be discussed with an experienced professional.

These measures may limit factors that contribute to spots. They do not guarantee that spots will disappear or that new marks will not appear.

Post-inflammatory hyperpigmentation may fade, but its course depends on the cause and the depth of the pigment. Sun protection, well-tolerated products and managing inflammation remain essential. You can seek advice about a persistent mark or one with an unclear cause before choosing treatment.