🔬What is PIH? (Post-Inflammatory Hyperpigmentation) – Clinical Definition & Types
Post-Inflammatory Hyperpigmentation (PIH) is a common skin condition where dark marks remain on the skin after inflammation or injury has healed.
PIH is not an active infection or disease. It is a pigment response that occurs after skin inflammation.
🧬 How PIH Forms
PIH develops when the skin experiences inflammation such as:
acne lesions
irritation from skincare products
physical injury or trauma
allergic reactions
excessive friction or rubbing
During the healing process, melanocytes become activated and produce excess melanin as part of the skin’s defense response.
This melanin is then deposited unevenly in the skin, creating visible dark marks.
☀️ Relationship to UV and Inflammation
PIH becomes more persistent when inflammation is combined with:
UV exposure (UVA & UVB)
repeated irritation
weakened skin barrier function
These factors increase melanocyte activity and slow down the fading process of pigmentation.
🧬 Types of PIH (Clinical Classification)
PIH can be seen in two main layers of the skin:
1. Epidermal PIH
occurs in the upper skin layer
brown or light brown color
usually fades over time
responds better to treatment
2. Dermal PIH
occurs deeper in the skin
gray, bluish, or darker tone
slower to fade
more resistant to treatment
Many cases exist as a combination of both.
⚪ Post-Inflammatory Hypopigmentation (Rare Case)
In most clinical cases, post-inflammatory changes result in increased pigmentation (PIH).
However, in rare cases, inflammation can lead to reduced melanin production, resulting in lighter patches known as post-inflammatory hypopigmentation.
This occurs when melanocyte activity is temporarily suppressed after inflammation or injury.
🧬 Clinical Observation
In my 18 years of experience as a medical esthetician, I have observed only a very small number of post-inflammatory hypopigmentation cases (approximately two cases in total).
This highlights that it is a rare condition compared to typical PIH.
⚠️ Possible Causes
strong inflammatory reactions
skin injury or trauma
aggressive cosmetic treatments
prolonged irritation or dermatitis
🧠 Key Difference
PIH → excess melanin (dark marks)
Hypopigmentation → reduced melanin (light patches)
🧠 Clinical Insight
PIH severity depends on:
intensity of inflammation
skin type and melanin activity
UV exposure during healing
barrier health condition
frequency of repeated irritation
This is why similar acne conditions can result in very different pigmentation outcomes.
✨ Key Takeaway
PIH is a pigment response triggered by inflammation, not a primary skin disease.
It occurs when melanocytes produce excess melanin during the healing process, especially in skin exposed to UV or repeated irritation.
Understanding the type and behavior of pigmentation is essential for correct treatment.
🧠Related Reading:
Angelina
Medical Esthetician (18 years experience)
Skin Logic by Angelina
