Post-Inflammatory Hyperpigmentation (PIH): Why Acne Leaves Dark Marks

If your acne has healed but you're left with flat brown, grey or tan marks, you're most likely experiencing Post-Inflammatory Hyperpigmentation (PIH).

PIH is one of the most common after-effects of acne and is often mistaken for scarring. Although these marks can persist for months, they are not true acne scars. Instead, they are changes in skin colour caused by inflammation and, with patience and the right skincare, they usually fade over time.

Understanding why PIH develops, who is most affected and how to support your skin can help you set realistic expectations and reduce the likelihood of future marks.

What is Post-Inflammatory Hyperpigmentation (PIH)?

Post-Inflammatory Hyperpigmentation is a flat area of darker pigmentation that remains after an inflamed acne lesion has healed.

When the skin becomes inflamed, pigment-producing cells called melanocytes respond by producing additional melanin. This extra pigment remains after the spot has disappeared, creating a flat mark that may appear:

• Brown.
• Tan.
• Grey.
• Darker than the surrounding skin.

Importantly, the skin remains smooth.

Unlike acne scars, PIH does not involve a change in the skin's texture. Only the colour has changed.

Why does acne cause PIH?

Inflammation is the key trigger.

The more inflamed a spot becomes, the greater the likelihood that extra pigment will be produced during healing.

This explains why:

• Large inflamed spots are more likely to leave marks.
• Picking or squeezing acne increases the risk.
• Repeated inflammation often leads to repeated pigmentation.

Reducing inflammation early is one of the best ways to prevent new PIH from developing.

Who is most likely to develop PIH?

Although anyone can develop PIH, it is particularly common in people with:

• Medium skin tones.
• Olive skin.
• Brown skin.
• Darker skin tones.

These skin types naturally contain more active melanin-producing cells, making them more responsive to inflammation.

As a result, pigmentation may:

• Be darker.
• Last longer.
• Be more noticeable.

This doesn't mean lighter skin cannot develop PIH, but it is generally less persistent.

How long does PIH last?

PIH fades gradually.

For many people, improvement occurs over several months, although deeper pigmentation can take considerably longer.

The exact timeline depends on several factors, including:

• Your skin tone.
• The severity of the original inflammation.
• Sun exposure.
• Whether new acne continues to develop.

Patience is an important part of recovery.

Because pigment naturally clears slowly, consistency is far more important than searching for a quick solution.

What helps PIH fade?

Daily sunscreen

Sun protection is the single most important step.

Ultraviolet light stimulates melanin production, making existing marks darker and prolonging the time they remain visible.

Using a broad-spectrum sunscreen every day helps protect healing skin and supports gradual fading.

Protect your skin barrier

Healthy skin heals more efficiently.

Choose a simple routine that includes:

• Gentle cleansing.
• Regular moisturising.
• Avoiding harsh scrubs and over-exfoliation.

Reducing irritation helps prevent further inflammation.

Prevent new acne

Every new inflamed spot has the potential to create another area of PIH.

Managing active acne is therefore one of the most effective ways to prevent ongoing pigmentation.

Some over-the-counter skincare ingredients may also help support a more even skin tone over time, but new products should always be introduced gradually to minimise irritation.

Can PIH be prevented?

While it cannot always be avoided completely, the risk can be significantly reduced by:

• Treating acne early.
• Avoiding picking or squeezing spots.
• Using daily sunscreen.
• Keeping your skincare routine gentle and consistent.

Preventing inflammation is always easier than treating pigmentation afterwards.

Frequently Asked Questions

Is PIH an acne scar?

No. PIH is a flat colour change caused by increased pigment. Acne scars involve permanent changes in skin texture.

Why is my PIH taking so long to fade?

PIH naturally improves slowly. Richer skin tones, deeper pigmentation and ongoing sun exposure can all prolong the process.

Can I stop PIH from developing?

Reducing inflammation, avoiding picking and protecting your skin from the sun are the most effective ways to reduce the likelihood of new pigmentation.

Does sunscreen really help?

Yes. Daily sunscreen is one of the most important ways to prevent PIH from darkening and to support gradual fading.

Should I worry if my marks last for months?

Not necessarily. PIH commonly persists for several months before gradually improving. The important point is that it differs from true scarring because the skin remains completely smooth.

Reviewed by Dr Tara Treacy, GP with a special interest in dermatology (IMC 411337).

Last reviewed: 16/07/2026.

General information only. It does not replace an individual medical assessment.