Melasma vs Lentigo vs PIH vs ABNOM: How to Tell Them Apart

This is an English adaptation of a clinical article Dr. SangYoul Yun — board-certified dermatologist and Medical Director of Delight Dermatology in Gangnam, Seoul — originally published in Korean. Read the Korean original on Naver. It has been restructured and translated for international readers; all references are the author's own.

"I read online and got a melasma laser, but they say it didn't work — that it wasn't actually melasma?" I hear this often in clinic. Yes, exactly. Brown marks on the face look similar on the surface but are medically completely different diseases, and a wrong diagnosis means treatment either fails or makes things worse.

Melasma, solar lentigo, post-inflammatory hyperpigmentation (PIH), and ABNOM (acquired bilateral nevus of Ota-like macules) are the four pigment disorders most common — and most often confused — in Korean women. Here is how to distinguish them, with the clinical diagnostic criteria.

1. Why accurate differentiation matters

The bottom line first: the effective treatment differs completely by disorder. Melasma needs gentle toning with adjunct medication, and using lentigo treatments (strong IPL or high-power lasers) makes melasma worse.¹ ABNOM, with pigment in the dermis, barely responds to superficial lentigo treatments,² and PIH recurs after a procedure unless the causative inflammation is controlled first. So the first thing we do in clinic is diagnose exactly "which pigment disorder is this" — if the diagnosis is wrong, treatment inevitably fails.

2. The four main pigment disorders, distinguished

① Melasma

• Location: symmetric on the cheeks, forehead, upper lip; spares the eyelids³
• Shape: brown patches with blurred borders (irregular, large areas)
• Cause: multifactorial — hormones, UV, heat, pregnancy, oral contraceptives, chronic inflammation
• Dermoscopy: uniform yellow-brown pigment plus a fine capillary network (seen in about 74%)⁴
• Wood's lamp: epidermal type darkens; dermal type shows little change⁴
• Key clue: symmetry and a link to hormonal change (onset/worsening after pregnancy or the pill)

② Solar lentigo

• Location: asymmetrically scattered on sun-exposed areas (forehead, temples, cheeks, backs of hands)
• Shape: small brown macules with sharp borders (usually under 5 mm)
• Cause: chronic UV exposure (photoaging) is the biggest driver
• Wood's lamp: darkens more distinctly (because it is epidermal pigment)⁴
• Key clue: once formed, it doesn't fade without sun protection (persists even in winter)⁵

Note — freckles (ephelides) are also small brown macules, but they darken in summer and fade in winter, distinguishing them from solar lentigo. Freckles appear from childhood and have a strong genetic component.⁵

③ Post-inflammatory hyperpigmentation (PIH)

• Location: exactly where prior inflammation, trauma, or acne occurred
• Shape: brown to gray-brown deposition in the shape of the former inflammation
• Cause: the aftermath of any skin inflammation — acne, eczema, dermatitis, peels, laser procedures
• Dermoscopy: uniform brown or gray-brown pigment¹
• Key clue: a distribution matching the inflammatory lesions (acne-scar sites, mosquito bites, etc.)

Caution: the darker the skin (Fitzpatrick IV–VI), the far higher the rate of PIH.¹ Koreans are a skin type prone to PIH, so minimizing inflammation is central to any procedure.

④ ABNOM (acquired nevus of Ota-like macules / Hori's nevus)

• Location: symmetric on both cheekbones, temples, and beside the nose; does not involve mucosa (eyes, mouth)⁶
• Shape: clustered bluish gray-blue to blue-brown dots
• Cause: melanocytes located in the deep (mid) dermis — acquired dermal melanocytosis^6,7
• Wood's lamp: unlike superficial pigment, it does not darken further under Wood's lamp (deep dermal pigment)
• Key clue: mainly found in women in their 30s–40s⁶, a bluish hue (melasma is yellow-brown), and — being deep in the dermis — barely responds to superficial treatments like toning

Clinical tip: ABNOM is the most common acquired dermal pigment disorder in Korean, Japanese, and Chinese women. Very often patients come in after being treated for "melasma" with no result.

3. At-a-glance differential table

Melasma vs lentigo vs PIH vs ABNOM — differentiation summary

Feature	Melasma	Lentigo	PIH	ABNOM
Distribution	Symmetric patches	Scattered on sun-exposed areas	Sites of inflammation	Symmetric on cheekbones/temples
Shape	Large area, blurred border	Small dots, sharp border	Shape of the inflammation	Small blue dots
Color	Yellow-brown	Brown to dark brown	Brown to gray-brown	Blue-gray / blue-brown
Depth	Epidermal–dermal mixed	Epidermal	Epidermal–dermal	Deep dermis
Wood's lamp	Epidermal type darkens	Darkens	Superficial darkens	Little change
Main cause	Hormones, UV	Chronic UV	Prior inflammation	Acquired dermal melanocytes
Typical age	Women 20s–40s	Middle-aged to older	All ages	Women 15s–40s

4. How we diagnose — the clinic's pigment tools

For pigment-disorder care we use the following tools together.

• Wood's lamp — a UV wavelength assesses pigment depth. Epidermal pigment appears darker; dermal pigment shows little change or looks fainter.⁸
• Dermoscopy — 10× magnification observes pigment patterns directly, distinguishing melasma's capillary network, lentigo's sharp border, and ABNOM's gray-blue dots.⁴
• META VIEW skin analysis — multi-wavelength imaging quantifies surface pigment, deep pigment, erythema, and UV damage.
• Clinical history — a full review of onset, hormonal change, pregnancy, medication use, and prior inflammation.

5. Different diagnosis, completely different treatment

Recommended treatment direction by disorder

Disorder	Recommended treatment direction
Melasma	Low-irritation toning + adjunct drugs such as tranexamic acid + strict sun protection (strong lasers contraindicated)1
Lentigo	Superficial pigment-targeting procedures such as pico / QS laser + sun protection
PIH	Treat the causative inflammation first + anti-inflammatory topicals + low-irritation procedures
ABNOM	Dermal-pigment-targeting lasers such as 1064 nm Q-switched Nd:YAG (multiple sessions needed)2,6

Even for the same brown, the treatments are often opposite. Melasma and lentigo look alike in color but need opposite treatment directions, and using lentigo's strong IPL on melasma darkens the melasma.¹

6. The most common misdiagnoses

• ABNOM mistaken for melasma — bluish pigment on both cheekbones diagnosed as "melasma" and toned repeatedly with no improvement. It is actually ABNOM — dermal pigment that shallow toning can't reach.
• PIH mistaken for melasma — brown acne marks lingering and mistaken for melasma. It is actually PIH; the acne inflammation must be controlled first, with anti-inflammatory treatment taking priority.
• Dermal melasma mistaken for lentigo — a small, relatively sharp-bordered melasma patch treated as lentigo with strong IPL → melasma worsens with accompanying PIH.
• Melasma–ABNOM mixed — one patient often has both, requiring the appropriate treatment for each in stages.⁶

7. How we approach pigment at Delight Dermatology

Diagnosis first, treatment second — a full assessment with dermoscopy and META VIEW. Because one patient can have several disorders together, we account for mixed types, and because Korean skin is at high risk of PIH, we prioritize low-irritation approaches. Since most pigment disorders recur, we treat them long-term as "management" rather than a "cure."

Bottom line: not all "brown marks" are the same. Melasma, lentigo, PIH, and ABNOM look alike but are separate diseases with completely different causes, depths, and treatments. Before choosing a procedure based on online information or advertising, get an accurate differential diagnosis.

References

1. Honigman A, Lim AC, Murase JE. Differential diagnosis of melasma and hyperpigmentation. Dermatological Reviews. 2023.
2. Ee HL, Goh CL, Khoo LS, et al. Treatment of acquired bilateral nevus of Ota-like macules (Hori's nevus) with a combination of the 532 nm Q-switched Nd:YAG laser followed by the 1064 nm Q-switched Nd:YAG is more effective: prospective study. Dermatol Surg. 2006;32(1):34-40.
3. Passeron T, Picardo M. Melasma, a photoaging disorder. Pigment Cell Melanoma Res. 2018;31(4):461-465.
4. Wang L, Xu AE. Dermoscopy combined with Wood lamp, a diagnostic alternative for five pigmented lesions on the face: an observational study. Chin Med J (Engl). 2020.
5. Praetorius C, et al. Ephelides and lentigines: clinical and genetic features. DermNet NZ. 2023.
6. Hori Y, Kawashima M, Oohara K, Kukita A. Acquired, bilateral nevus of Ota-like macules. J Am Acad Dermatol. 1984;10(6):961-964.
7. Cho SB, et al. Treatment of acquired bilateral nevus of Ota-like macules (Hori's nevus) using 1064-nm Q-switched Nd:YAG laser with low fluence. Int J Dermatol. 2009;48(12):1308-1312.
8. Sonthalia S, et al. Evaluation of Dermoscopic Features in Facial Melanosis with Wood Lamp Examination. Clin Cosmet Investig Dermatol. 2022;15:215-227.

Medical disclaimer. This article is general information and does not replace individual consultation. In pigment disorders, differential diagnosis decides success or failure, so diagnosis and procedure selection should be decided after an in-person consultation with a dermatologist. The wrong procedure can worsen pigmentation, and results and recovery vary between individuals.