Post-Inflammatory Hyperpigmentation (PIH)

What causes post-inflammatory hyperpigmentation

When skin is inflamed or injured, the immune response releases chemical signals (such as prostaglandins and leukotrienes). These stimulate melanocytes, the pigment-making cells, to produce more melanin and pass it to surrounding skin cells.

There are two depths:

• Epidermal PIH: extra pigment in the top layer of skin. Brown, with clearer edges, and fades in months.
• Dermal PIH: inflammation damages the lower layer, and pigment drops into the dermis, where it is engulfed by cells called melanophages. Gray-blue or slate colored, fades slowly and responds less to creams.

Common triggers:

Sun exposure darkens PIH and slows fading, and visible light (not only UV) also contributes in darker skin.

Symptoms and appearance

• flat (not raised or sunken) spots or patches
• colors from light brown to dark brown or black (epidermal) or gray-blue (dermal)
• located exactly where the previous inflammation was
• no itch or pain once the original problem has settled

PIH vs acne scars and other dark spots

Pink or red marks after acne in lighter skin are called post-inflammatory erythema (PIE). They come from small blood vessels, not pigment, and respond to different treatments. Melasma and general skin darkening are covered on the hyperpigmentation page.

Diagnosis

A dermatologist diagnoses PIH from its appearance and the history of a preceding rash or injury. A Wood's lamp (UV light) exam can suggest whether pigment is epidermal or dermal. A biopsy is rarely needed, except when a spot looks unusual.

How to treat post-inflammatory hyperpigmentation

1. Stop the inflammation

New marks keep forming until the cause is controlled. Treating acne early, ideally with medicines that also fade pigment, is the single most effective step. Avoid picking, squeezing or scratching.

2. Sun protection every day

Use a broad-spectrum sunscreen of SPF 30 or higher daily, even indoors near windows. Tinted sunscreens with iron oxides also block visible light, which is especially helpful for darker skin. Reapply every 2 hours outdoors.

3. Fading treatments

Results take 8 to 12 weeks or longer. Introduce one product at a time, because irritation itself can cause new PIH.

• Azelaic acid (15% to 20%): treats acne and fades pigment; well tolerated.
• Retinoids: adapalene (available over the counter), tretinoin and tazarotene speed skin turnover and treat acne.
• Hydroquinone: a strong pigment inhibitor, available in the US by prescription at 4%. It is used in courses, usually 3 to 6 months, under medical guidance, because long-term use can rarely cause dark blue-black discoloration (ochronosis).
• Triple-combination cream: hydroquinone, tretinoin and a mild steroid, prescription only, for short courses.
• Other ingredients: niacinamide, vitamin C, kojic acid, tranexamic acid, licorice extract and cysteamine. Evidence is moderate but they are gentle options.

4. Procedures

• Chemical peels: glycolic or salicylic acid peels in a series can help. Deeper peels carry a risk of worsening PIH in darker skin.
• Lasers: low-energy Q-switched or picosecond lasers and some fractional lasers can help stubborn PIH, but must be used cautiously by experienced practitioners.
• Microneedling: sometimes combined with fading agents.

Dermal PIH responds poorly to creams and may take years to fade.

How long does PIH last?

Epidermal PIH typically fades in 3 to 12 months with sunscreen and treatment. Dermal PIH can persist for years and sometimes permanently. Repeated sun exposure, ongoing acne or eczema, and picking extend the time.

Preventing new dark marks

• Treat acne and eczema early and consistently.
• Do not pick, pop or scratch.
• Use gentle cleansers and avoid harsh scrubs.
• Wear sunscreen daily.
• Before laser or peel procedures, tell the practitioner if you develop dark marks easily; pre-treatment with fading agents may be recommended.
• Patch test new products on a small area first.

Frequently asked questions

How long does post-inflammatory hyperpigmentation take to fade?

Marks in the upper skin layer usually fade in 3 to 12 months, faster with daily sunscreen and fading treatments. Deeper, gray-blue PIH can take years. Each new breakout or sunburn can reset the clock, so controlling the cause matters.

What is the fastest way to get rid of PIH?

Combine daily broad-spectrum sunscreen with a fading agent such as azelaic acid, a retinoid or prescription hydroquinone, and treat the underlying acne or eczema. Chemical peels or careful laser treatment can speed results in stubborn cases. Expect visible improvement after about 8 to 12 weeks.

Is PIH permanent?

Usually not. Most epidermal PIH fades completely with time. Dermal PIH, where pigment is deeper, can last for years and may not fully disappear. Sun protection and avoiding further inflammation give the best chance of clearing.

What is the difference between PIH and acne scars?

PIH is flat discoloration from extra pigment and usually fades. Acne scars change the skin's texture, appearing as pits, depressions or raised bumps, because collagen is damaged. Scars do not fade on their own and need procedures such as lasers, microneedling or subcision.

Does vitamin C help post-inflammatory hyperpigmentation?

Topical vitamin C has antioxidant and mild pigment-reducing effects and can help fade PIH, especially combined with sunscreen and other agents. It is less powerful than hydroquinone or retinoids. Stable formulations and consistent use for several months are needed to see results.