SkincareSafety Guide

Skin

Understand your skin type, tone, and what your skin is doing.

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Start here

Skin typesThe main skin types and how they differ.Find your skin typeA practical identification guide.What different skin types look likeVisual differences between common skin types.

Common skin questions

Oily skinWhat oily skin means and how to read it.Skin type changesHow skin type can shift over time.Skin type and ageHow visible aging differs by skin type.
Not sure where to start?Use the skin-type guide before choosing routines or ingredients.

Concerns

Start from a skin problem or visible change.

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Oil and acne

Why oily skin happensThe main drivers behind excess oil.Oily skin and acneHow oil can contribute to breakouts.Can oily skin cause acne?A direct answer to the oil-acne link.

Changes and warning signs

Stress and oily skinHow stress may affect oiliness.Dehydration and oilinessWhy skin can feel oily and dehydrated.Skin cancer signsVisual signs that need professional attention.
Looking for a solution?Start with what oily skin actually needs before adding stronger products.

Ingredients

Understand what ingredients do and whether they fit your skin.

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Explore ingredients

NiacinamideA practical ingredient overview.Vitamin C serumWho can use vitamin C and when to be careful.RetinolHow retinol fits different skin types.

Use safely

Salicylic acidWhere this acne-focused ingredient fits.Niacinamide for all skin typesSuitability across skin types.Ingredient comparisonsUse comparisons to avoid mismatched decisions.
Can my skin use this?Browse compatibility questions before adding a new active.

Routines

Turn skin information into daily decisions.

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Daily basics

Does every skin type need moisturizer?A basic routine decision.Does every skin type need sunscreen?Where SPF fits in daily care.What oily skin needsA simple care direction for oily skin.

Adjust over time

Skin changes with ageWhen your routine may need to change.Seasonal skin changesHow weather affects skin behavior.Korean skincare approachWhat is useful beneath the trend.
Starting from scratch?Begin with moisturizer, sunscreen, and one skin-specific need.

Products

A small selection of skincare products recommended by OuterDerm for simple, effective everyday routines.

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Recommended picks

Daily SunscreenDaily UV protection that has to be wearable enough to stick with.Azelaic AcidA focused 10% azelaic acid when uneven tone or blemish marks are the concern.Gentle CleanserComfortable cleansing when tight or squeaky skin is a warning sign.
Not sure where to start?Browse three carefully selected essentials, then ask on WhatsApp before you order.

Learn

Go deeper into skin science, myths, evidence, and safety.

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Hazardous ingredients

Safety hubStart with mercury, steroids, PPD and other hazardous substances.Ingredient safety indexBrowse Phase 1 and Phase 2 hazardous ingredients.Mercury in whitening creamsLabel names, Punjab alerts, and what to do now.

Product literacy

Product literacy hubHow to read labels, claims, and INCI lists before you buy.How to read an ingredient labelINCI order, Parfum, and missing-list red flags.Fragrance-free vs unscentedHow to verify a fragrance-free claim on the ingredient list.How to choose sunscreenBroad spectrum, wearability, and a readable pack — not a fairness claim.

Skin science

Skin color geneticsHow inherited traits shape skin color.Skin color typesHow skin tone is commonly grouped.Are skin types genetic?What genetics can and cannot explain.

Evidence and myths

Can all skin types tan?Tanning, risk, and skin type.Is oily skin good or bad?A balanced view of oily skin.Why Korean skin looks flawlessTrend claims translated into practical basics.
Want the evidence layer?Use why-guides when you want causes, mechanisms, and context.

Skin Conditions & Concerns

What Is Post-Inflammatory Hyperpigmentation (PIH)?

You've dealt with the acne, the eczema, or the cut. It healed, but now you're left with a dark spot that won't go away. That's post-inflammatory hyperpigmentation (PIH). It's one of the most common forms of hyperpigmentation, and it's also one of the most treatable.

Quick answerPost-inflammatory hyperpigmentation (PIH) is the darkening of the skin that occurs after inflammation, such as from acne, eczema, or injury.

Medically reviewed by Dermatology reviewer · Updated Jul 18, 2026 · 4 min read

Illustration showing PIH dark spots on the face after acne
DefinitionDark spots left after inflammation
Common CausesAcne, eczema, cuts, burns
AppearanceFlat, dark spots
Best TreatmentNiacinamide, retinoids, acids
Key PreventionSunscreen and treating inflammation

Key answer

Manageable condition

PIH is a common condition that responds well to consistent treatment. Patience and sun protection are key.

Evidence
Strong - Manageable condition
Best for
Those with dark spots after acne or inflammation; Anyone looking to understand and treat PIH
Limitation
Those seeking a quick cure

See what the evidence shows

Short version

Story in brief

Post-inflammatory hyperpigmentation occurs when inflammation triggers an overproduction of melanin in a specific area of the skin. This can happen after acne, eczema, psoriasis, a cut, a burn, or any other type of skin injury.

The inflammation stimulates melanocytes to produce more melanin, which is then transferred to the skin's surface. The result is a flat, dark spot that persists after the inflammation has resolved.

PIH is more common and more severe in people with darker skin types. It can persist for months or even years, but it's treatable. The most effective approach is a combination of sun protection and targeted treatments.

Mental model

Visual explanation

Evidence

What the evidence shows

PIH is not a scar - it's a pigmentation change. Unlike scars, which are changes in skin texture, PIH is a change in color that can be treated and often fades with time.

  • Understanding of mechanism

    Understanding of mechanism

  • Treatment options

    Treatment options

  • Prevention strategies

    Prevention strategies

Use this section to decide

Does this advice apply to me?

Find the concern or goal closest to yours, then use the fit signal to decide how much weight to give this guide.
Strong fit means the advice is central to that goal.Depends means formula, tolerance, or context matters more.Use caution means do not treat it as the main answer.

  • If your goal is

    DefinitionUsually relevant
    Fit signal
    Often useful

    Dark spots from inflammation

  • If your goal is

    Common CausesUse caution
    Fit signal
    Limited evidence

    Acne, eczema, injury

  • If your goal is

    Best TreatmentUse caution
    Fit signal
    Limited evidence

    Sunscreen + niacinamide

  • If your goal is

    Key TipUse caution
    Fit signal
    Limited evidence

    Treat inflammation early

Research notes already in this guide

  • PIH is well-documented as a response to inflammation.
  • Research shows it's more common in darker skin types.
  • Studies demonstrate effective treatments for PIH.

Explanation

How it works

  1. Inflammation occurs

    Acne, eczema, or injury triggers inflammation.

  2. Melanocytes are activated

    Inflammatory cytokines stimulate melanocytes.

  3. Excess melanin is produced

    Melanocytes produce more melanin than needed.

  4. Dark spot appears

    The excess melanin is transferred to the surface, leaving a dark spot.

Expected results

Results and timeframe

It can take time to fade, but it's treatable.

Practical use

How to use it

  1. Treat the underlying condition

    Control acne, eczema, or other sources of inflammation.

  2. Use sunscreen daily

    Sun protection is essential for fading PIH.

  3. Consider targeted treatments

    Niacinamide, retinoids, and acids can help fade spots.

Safety

Side effects and cautions

  • Confusing PIH with acne scars

    PIH is a pigmentation change, not a structural scar.

  • Not treating the underlying inflammation

    Treating acne or eczema can prevent new PIH.

  • Skipping sunscreen while treating PIH

    Without sunscreen, PIH can darken and persist.

Fit

Who should be careful

  • Those seeking a quick cure

Worth noting

Small details that can change the answer

  • PIH vs. Scars. PIH is a pigmentation change, not a structural change in the skin.
  • Darker Skin Risk. PIH is more common and more severe in darker skin types.
  • Fading Time. PIH can take months to years to fade without treatment.
  • Treatment Response. PIH often responds well to topical treatments.

PIH is dark spots left after inflammation, such as from acne.

It's caused by excess melanin production in the affected area.

PIH is more common in darker skin types.

Treatment includes sunscreen, niacinamide, retinoids, and acids.

Definition

Understanding post-inflammatory hyperpigmentation

PIH is the darkening of the skin that follows inflammation. It's caused by excess melanin production in the affected area. PIH is flat, usually dark brown or black, and persists after the inflammation has healed.

  • Caused by inflammation (acne, eczema, injury)
  • Appears as flat, dark spots
  • More common in darker skin types
  • Treatable with topical treatments

Science

The science of PIH formation

Inflammation triggers the release of inflammatory cytokines, which stimulate melanocytes to produce more melanin. The excess melanin is then transferred to keratinocytes, leading to a localized increase in pigmentation. The darker the skin, the more pronounced the effect.

Inflammatory Cytokines
Signaling molecules released during inflammation that can stimulate melanocytes.
Melanocyte
A cell in the basal layer of the epidermis that produces melanin.

Questions

Frequently asked questions

Is PIH permanent?

No, it can fade with treatment, but it may take months.

Does PIH go away on its own?

It can, but it often takes months to years without treatment.

What is the best treatment for PIH?

A combination of sunscreen, niacinamide, and chemical exfoliants is often effective.

Can PIH be prevented?

Treating inflammation early and using sunscreen can help prevent PIH.

References

Sources

The notes below are drawn from the evidence already cited in this guide. They are not a complete bibliography.

  1. PIH is well-documented as a response to inflammation.
  2. Research shows it's more common in darker skin types.
  3. Studies demonstrate effective treatments for PIH.