TL;DR: Three of the most common reasons a dark patch won’t fade are post-inflammatory hyperpigmentation, melasma, and Hori’s nevus. They look similar in the mirror and respond very differently to treatment. PIH is in the epidermis and treatable. Melasma sits in both layers and is chronic. Hori’s nevus is dermal and resistant to topicals entirely. If you have spent six months on niacinamide and azelaic acid and seen no change, the issue may be that you are treating the wrong condition.
A reader who had been working on a “stubborn dark patch” on her cheeks for two years sent me her routine last fall. She was using azelaic acid 10 percent, niacinamide 5 percent, daily mineral SPF, and twice-weekly glycolic acid. None of it had touched the pigmentation. Her dermatologist had labeled it melasma and added hydroquinone. After six months on hydroquinone, the pigment was lighter in a few spots and unchanged across most of the patch.
When she sent photos, two things were visible that the labeling had missed. The pigment had a slight blue-gray cast in the symmetrical malar areas, not the brown of typical melasma. And the patch was strictly bilateral, with sharp edges that did not blend into the surrounding skin the way melasma typically does.
She did not have melasma. She had Hori’s nevus, also called acquired bilateral nevus of Ota-like macules. The dermatologist had not done the differential, and she had been treating a dermal pigmentation problem with topicals that only reach the epidermis. No amount of azelaic acid was going to move dermal melanocytes.
This is a more common scenario than the hyperpigmentation marketing acknowledges. The shelves are full of brightening serums. The diagnostic that determines whether any of them will work for your specific patch is rarely done.
The three conditions, briefly
Post-inflammatory hyperpigmentation (PIH) is the pigmentation that develops after skin inflammation. Acne, eczema, allergic reactions, burns, ingrown hairs, even an aggressive exfoliation. The melanocytes in the inflamed area produce excess melanin, which deposits in the epidermis and sometimes the upper dermis. Davis and Callender’s 2010 review in the Journal of Clinical and Aesthetic Dermatology covers PIH in skin of color in detail. The key features for differential: it follows a known inflammatory event, it sits where the inflammation was, and it is typically tan-to-brown in lighter skin and darker brown to almost black in deeper skin tones. PIH fades over months to years. Treatments accelerate this; they do not invent the fade.
Melasma is a chronic, often symmetrical, hormonally and UV-driven pigmentation that typically appears on the upper cheeks, forehead, upper lip, and bridge of the nose. It is bilateral, with a soft-edged distribution that blends into surrounding skin. Handel’s 2014 review in Anais Brasileiros de Dermatologia and Sarkar’s 2014 melasma update in the Indian Dermatology Online Journal both describe the same pattern: female predominance (around 90 percent of cases), onset frequently linked to pregnancy or hormonal contraception, deep tan to brown color, sometimes with both epidermal and dermal components. Melasma has three classifications by pigment depth: epidermal (responds best to topicals), dermal (resistant to most topicals), and mixed (the most common, partial response). Passeron and Picardo’s 2018 work in Pigment Cell & Melanoma Research reframed melasma as a photoaging disorder, which is an important shift in how we think about treatment.
Hori’s nevus is acquired bilateral nevus of Ota-like macules, a pigmented condition that typically appears in adulthood in people of East Asian, South Asian, and sometimes Southeast Asian descent. Lee’s 2015 work in the International Journal of Dermatology covers the clinicopathologic features. The pigmentation is dermal, sitting deeper than melasma, often with a slate-gray or bluish hue. The lesions are bilateral and symmetric, typically on the malar cheeks, sometimes extending to the temples, forehead, or nose. They have sharper borders than melasma and do not blend into surrounding skin. Hori’s does not respond to topical lightening agents at all, because the pigment is below the depth that topicals reach. It is treated almost exclusively with laser, most commonly Q-switched Nd:YAG or picosecond lasers.
A patch of pigment on the cheeks could be any of these three. They get confused for each other constantly. The treatments diverge enough that the misdiagnosis costs years.
The differential, practical version
The features that help separate them, in the order I would actually look at them:
Onset and trigger. PIH follows inflammation, almost always. If the dark area sits exactly where a pimple was eight months ago, or where you scratched the eczema patch, it is PIH until proven otherwise. Melasma typically starts during pregnancy, hormonal contraception start, or after substantial UV exposure, and develops over weeks to months. Hori’s appears spontaneously, usually in the third or fourth decade, with no clear inciting event.
Color. PIH is brown, sometimes with a slight pink to it in early stages, deepening to deeper brown over time. Melasma is brown to tan, usually warm-toned, sometimes with a hint of yellow. Hori’s has the slate-gray or blue-gray quality of dermal pigment; the same way a dermal mole can look bluish from the dermal melanocyte depth.
Borders. PIH has the shape of the original inflammation. Often a discrete spot the size of the pimple that caused it, sometimes coalesced patches. Melasma has soft, fuzzy borders that fade gradually into surrounding skin. Hori’s has sharper, more defined borders that interrupt the surrounding skin rather than melting into it.
Distribution. PIH is wherever the inflammation was, often asymmetric. Melasma is bilateral and broadly symmetrical, with characteristic distribution patterns (centrofacial, malar, mandibular). Hori’s is strictly bilateral, almost mirror-image symmetric, focused on the malar prominences.
Response to topicals. This is the cleanest separator. PIH responds well over six months to a year of azelaic acid, kojic acid, vitamin C, niacinamide, and tretinoin. Melasma responds partially, often relapses, and requires sustained treatment plus aggressive UV protection. Hori’s does not respond meaningfully to any topical. If you have been on a serious brightening routine for six months and there is zero visible change, Hori’s is on the differential.
For readers trying to work through this differential without a dermatology appointment, /tools/hyperpigmentation-type runs through the same questions in a structured way. The output points to the most likely category, but a definitive diagnosis is still a dermatology visit, and for any pigment that is changing rapidly, asymmetric, or behaving unusually, the dermatology visit is the right first step regardless.
Why this matters for the routine
The treatment frameworks barely overlap.
For PIH: topical retinoids (tretinoin 0.025 to 0.05 percent), azelaic acid (10 to 20 percent), niacinamide, vitamin C, kojic acid, and aggressive daily SPF. The combination targets melanin production, transfer, and turnover. Time horizon: three to twelve months for substantial fade. /tools/tretinoin-decoder covers the specifics of starting tretinoin for PIH and what concentration matches your skin type.
For melasma: the same topicals are useful but the routine is structurally different. Sunscreen is the foundation, not the supplement. Visible-light protection (tinted mineral sunscreens with iron oxides) matters as much as UV protection. Hydroquinone 4 percent, often cycled (three months on, three months off), remains the most effective topical though it has its own issues with long-term use. Tranexamic acid, oral or topical, has emerging data. The Passeron framing of melasma as photoaging means UV avoidance, daily reapplication, and visible light protection are not optional. Treatment is indefinite; melasma does not “clear,” it gets managed. /tools/sunscreen-tracker walks through the daily reapplication discipline that makes more difference for melasma than any active.
For Hori’s: laser. Q-switched Nd:YAG 1064 nm or picosecond Nd:YAG at the same wavelength. Multiple sessions, typically four to eight, spaced six to twelve weeks apart. Topicals do not work. The brightening serum aisle is irrelevant. The investment is medical, in the thousand-to-several-thousand dollar range depending on geography and provider, and it is one of the few cosmetic dermatology interventions with a high satisfaction rate when correctly indicated.
The cost of misdiagnosis: a person treating Hori’s with azelaic acid and tretinoin will spend two years and several hundred dollars on a routine that cannot reach the pigment. A person treating melasma as if it were PIH will see early improvement, relapse, get frustrated, escalate the routine, damage the barrier, and possibly worsen the underlying melasma through inflammation. A person treating PIH as if it were melasma will overuse hydroquinone in a way that the PIH does not warrant.
The contrarian section: the dermatology visit is undervalued
A standard “brightening” consultation at a dermatologist’s office costs less than the cumulative spend on topical hyperpigmentation products that do not work. The visit can include Wood’s lamp examination, which separates epidermal pigment (brightens under UV light) from dermal pigment (does not brighten and may appear darker), and confocal microscopy or dermoscopy when the diagnosis is ambiguous.
The reason I am pushing this hard: hyperpigmentation is one of the few common cosmetic dermatology issues where the diagnostic determines the treatment, and the diagnostic is impossible to do reliably from photos or symptoms alone. The internet differential is a starting point. The clinical exam is the answer.
If you are in the United States or Europe and your insurance covers a dermatology visit even partially, use it. If you are paying out of pocket, one consultation visit (typically 150 to 300 dollars in the US, less in many other countries) is the highest-yield single skincare expenditure you can make for hyperpigmentation. Bring photos taken in consistent lighting over time. Bring your current routine. Ask specifically whether the pigment is epidermal or dermal. Ask whether laser is indicated.
If laser is recommended for Hori’s or for the dermal component of mixed melasma, get a second opinion from a derm who does the procedure regularly. Q-switched and picosecond lasers in inexperienced hands can cause post-inflammatory hyperpigmentation on top of the original lesion, which is a worse outcome than the starting condition.
What I do for the people I write back to
When a reader emails about stubborn hyperpigmentation, I ask the same three questions every time. What did the patch look like when it first appeared. Is it bilateral and symmetric. Has any treatment moved it at all over the past six months.
Patch following inflammation, asymmetric, partial fade on topicals over months: probably PIH, the routine is approximately right, give it more time.
Patch developed over pregnancy or pill change, bilateral with soft borders, partial fade on topicals that relapses with sun: probably melasma, the routine needs more sun protection and possibly hydroquinone cycling, but expect a long management horizon.
Patch appeared in adulthood with no clear trigger, bilateral with sharp borders, slate-gray quality, no movement on six months of topicals: probably Hori’s, get a derm to look, laser is the indicated treatment.
This is not diagnostic certainty. It is the differential that gets people to the right next step.
What this means
If your pigment is not moving, the most useful thing to do is not buy a stronger serum. It is to figure out what you are actually treating. The brightening category has good products for PIH. It has decent options for melasma when combined with rigorous photoprotection. It has essentially no options for Hori’s nevus, and the time spent applying brightening serums to dermal pigment is time the lasers could have been doing the actual work.
We do not yet have a topical that reliably treats dermal pigmentation. The research is ongoing on tranexamic acid, on novel tyrosinase inhibitors, on liposomal delivery. None of it is at the consumer shelf yet. Until it is, the differential is the most important skincare decision in this category, and the differential is a clinical exam, not a serum.
FAQ
How do I know if my melasma is epidermal, dermal, or mixed? Wood’s lamp examination in a dermatology office is the standard. Epidermal melasma becomes more visible under Wood’s lamp. Dermal melasma does not. Mixed shows both patterns.
Can PIH ever become permanent? Rarely. Most PIH fades over six to twenty-four months even without treatment, faster with treatment. Treatment-resistant cases sometimes have a dermal component that requires different management.
Is laser safe for skin of color? Q-switched Nd:YAG 1064 nm and picosecond Nd:YAG are the wavelengths with the better safety profile in darker skin. Other laser modalities have higher risk of post-inflammatory hyperpigmentation in skin of color. Provider experience with your skin type is the most important variable.
Can I treat Hori’s with topicals while saving up for laser? You can use the routine for general skin health and PIH prevention, but you should not expect movement of the Hori’s pigment itself. Realistic expectations prevent the frustration that drives barrier damage from escalating routines.
Does tranexamic acid work for melasma? Oral tranexamic acid has the better evidence for melasma improvement, typically prescribed at 250 to 500 mg per day. Topical tranexamic acid has weaker but emerging data. Both require dermatology supervision; oral tranexamic acid has clotting considerations that need screening.
Sources
Davis EC, Callender VD. “Postinflammatory hyperpigmentation: a review of the epidemiology, clinical features, and treatment options in skin of color.” Journal of Clinical and Aesthetic Dermatology, 2010.
Handel AC, Miot LDB, Miot HA. “Melasma: a clinical and epidemiological review.” Anais Brasileiros de Dermatologia, 2014.
Lee DJ, Park JH, Lee JH, Chang SE. “Acquired bilateral nevus of Ota-like macules (Hori’s nevus): a clinicopathologic study.” International Journal of Dermatology, 2015.
Sarkar R, et al. “Melasma update.” Indian Dermatology Online Journal, 2014.
Passeron T, Picardo M. “Melasma, a photoaging disorder.” Pigment Cell & Melanoma Research, 2018.
Related Elelaf tools
Sources
- Davis EC, Callender VD. Postinflammatory hyperpigmentation: a review of the epidemiology, clinical features, and treatment options in skin of color. Journal of Clinical and Aesthetic Dermatology 2010;3(7):20-31. PMID: 20725554.
- Handel AC, Miot LDB, Miot HA. Melasma: a clinical and epidemiological review. Anais Brasileiros de Dermatologia 2014;89(5):771-782. PMID: 25184917.
- Lee DJ, Park JH, Lee JH, Chang SE. Acquired bilateral nevus of Ota-like macules (Hori’s nevus): a clinicopathologic study with insight into the pathogenesis. International Journal of Dermatology 2015;54(2):e74-78. PMID: 25069900.
- Sarkar R, Arora P, Garg VK, et al. Melasma update. Indian Dermatology Online Journal 2014;5(4):426-435. PMID: 25396122.
- Passeron T, Picardo M. Melasma, a photoaging disorder. Pigment Cell & Melanoma Research 2018;31(4):461-465. PMID: 29285880.