Post-inflammatory hyperpigmentation (PIH) is the darkening of the skin that can remain after an acne lesion or other skin injury has healed. These spots are not active acne or true scars—they are areas where the skin has produced excess pigment in response to inflammation.
How PIH develops
The process generally follows these steps:
- Inflammation occurs.
An inflamed pimple triggers the body’s immune response. Immune cells release chemical messengers that help fight bacteria and repair damaged tissue. - Pigment-producing cells are stimulated.
These inflammatory signals also stimulate melanocytes, the cells that produce the pigment melanin. As a result, more melanin is made than usual. - Excess pigment is deposited.
The extra melanin accumulates in the skin. If the pigment remains in the upper layer of the skin (the epidermis), the spots are often tan to dark brown. If inflammation affects deeper layers and pigment reaches the dermis, discoloration may appear gray, blue-gray, or slate-colored and can take longer to fade. - The acne heals, but the pigment remains.
Once the pimple has resolved, the excess melanin may persist for weeks to months, or occasionally longer, until the skin gradually removes or redistributes it through normal renewal processes.
Who is more likely to develop PIH?
PIH can affect people of any skin tone, but it is more common and often more noticeable in individuals with medium to deep skin tones because melanocytes are generally more active.
It is also more likely to occur when:
- Acne is highly inflamed (such as papules, pustules, or nodules).
- Pimples are picked, squeezed, or scratched.
- Acne treatment is delayed, allowing inflammation to persist longer.
- Skin is exposed to significant ultraviolet (UV) light without protection.
What PIH looks like
Depending on your skin tone and the depth of the pigment, PIH may appear as:
- Light brown
- Dark brown
- Gray-brown
- Blue-gray
Unlike raised or depressed acne scars, PIH does not change the texture of the skin.
How long does it last?
The timeline varies, but in general:
- Mild epidermal PIH may fade over several months.
- Deeper pigmentation can take many months or longer.
- Sun exposure can prolong the fading process by stimulating additional melanin production.
Supporting recovery
Several measures can help PIH improve over time:
- Treat acne early to reduce ongoing inflammation.
- Avoid picking or squeezing blemishes.
- Use a broad-spectrum sunscreen with SPF 30 or higher every day to help prevent existing spots from becoming darker.
- Continue appropriate acne treatment to reduce the risk of new inflammatory lesions.
Certain topical ingredients, such as retinoids, vitamin C, or pigment-reducing agents, may also help improve PIH over time, but they should be used according to a healthcare professional’s guidance, especially if you have sensitive skin or are using other acne medications.
Although PIH can be frustrating, it is generally a temporary change in skin color rather than permanent scarring. With time, consistent sun protection, and effective acne management, many spots gradually become less noticeable.
