Key facts
- What it is
- Acquired dermal melanocytosis: pigment-producing cells in the dermis of both cheeks, named after Hori, who described it in 1984
- Who gets it
- Mostly women of East and Southeast Asian descent, with onset in the twenties to forties
- Where it sits
- Both malar areas symmetrically; sometimes the temples, forehead, nasal sidewalls and upper eyelids
- How it looks
- Discrete blue-grey, slate or grey-brown macules, speckled rather than a confluent patch, with no eye or mouth involvement
- Why creams fail
- Lightening agents act on epidermal pigment production; this pigment sits in the dermis beneath their reach
- Treatment
- Laser wavelengths that reach dermal pigment, such as 1064 nm, in staged conservative visits after melasma is excluded or controlled
- Main risk
- Post-inflammatory hyperpigmentation after laser, common in this condition and in Fitzpatrick III to V skin
What causes Hori's naevus?
Hori's naevus is caused by melanocytes, the cells that make pigment, lying in the dermis of the cheek skin instead of in the epidermis where they belong. Under the microscope the condition is dermal melanocytosis: spindle-shaped pigment cells scattered in the upper and middle dermis, producing melanin that is seen through the overlying skin as a blue-grey or slate colour because of the way light scatters from pigment at depth. Why these cells are there is not settled; proposals include melanocytes that failed to migrate fully during development and were later activated, and reactivation of dormant dermal melanocytes by hormones, sunlight or inflammation.
The condition was described by Hori in 1984 and is also called acquired bilateral naevus of Ota-like macules, abbreviated ABNOM. It appears in adulthood, typically from the twenties to forties, overwhelmingly in women and mostly in East and Southeast Asian skin, which makes it a routine presentation in Singapore rather than an unusual one. It often coexists with melasma, solar lentigines or freckles on the same face, and the facial pigmentation guide explains why several browns are usually sorted at one examination.
What does Hori's naevus look like, and how is it told apart from melasma?
Hori's naevus looks like a scattering of small, discrete blue-grey, slate-grey or grey-brown spots over both cheekbones, usually symmetrical, sometimes extending to the temples, the forehead, the sides of the nose and the upper eyelids. The spots stay separate rather than merging into a sheet, their colour has a bluish or grey cast, and they do not darken sharply after a sunny weekend the way melasma can. The whites of the eyes and the lining of the mouth are not involved, which separates it from naevus of Ota.
Melasma, by contrast, forms soft-edged, confluent light-to-dark brown patches on the cheeks, forehead or upper lip, fluctuates with sun, heat and hormones, and often shows a mottled rather than speckled texture. Freckles are small, light brown, scattered across sun-exposed skin and darken in the sun; solar lentigines are sharply bordered brown spots that accumulate with years of exposure. The difficulty is that these commonly share a face, and the melasma treatment page describes how the examination separates them. Dermoscopy and a Wood's lamp help: dermal pigment is poorly accentuated under Wood's light and shows a diffuse blue-grey pattern under the dermatoscope, while epidermal pigment is enhanced and shows a brown network.
“I will not fire a laser at an undiagnosed patch, and I would tell you to walk out of any clinic that will.”
Dr Sin YongOn diagnosis before any pigment laser
Why do creams and facials fail on Hori's naevus?
Creams fail because they act in the wrong layer. Hydroquinone, azelaic acid, tranexamic acid, retinoids and vitamin C reduce the production of pigment by epidermal melanocytes or speed the shedding of pigmented surface cells. In Hori's naevus the pigment cells sit in the dermis, below the basement membrane, where topical agents do not reach and where skin turnover does not carry pigment away. Facials, peels and exfoliation work on the surface for the same reason and leave the grey spots untouched; aggressive versions can inflame the skin and add brown post-inflammatory pigment over the grey.
This is the practical reason the diagnosis matters. A person treated for months with melasma creams whose cheek spots have not shifted may not have treatment-resistant melasma; they may have Hori's naevus, or both conditions together, in which case the melasma component responds to topicals and the dermal component does not.
Hori's naevus and the browns and greys it is confused with| Condition | Pattern and colour | Depth | What helps | What does not |
|---|
| Hori's naevus (ABNOM) | Discrete blue-grey to grey-brown spots over both cheekbones, speckled | Dermal | Conservative 1064 nm laser after diagnosis, staged with review | Lightening creams, facials, peels |
| Melasma | Soft-edged, confluent brown patches on cheeks, forehead or upper lip | Epidermal, dermal or mixed | Trigger control, photoprotection, topicals, cautious staged clinic work | Heat-based or aggressive laser |
| Freckles | Small light-brown spots across sun-exposed skin that darken in sun | Epidermal | Sun protection; pigment laser once confirmed | Treating them as a disease |
| Solar lentigines | Sharply bordered brown spots that accumulate with years of exposure | Epidermal | Daily sun protection; pigment laser if wanted | Unprotected sun exposure |
| Naevus of Ota | Usually one-sided blue-grey patch, often involving the white of the eye | Dermal | Dermal pigment laser after specialist eye assessment | Topicals |
| Post-inflammatory hyperpigmentation | Brown or grey marks at sites of earlier acne, injury or laser | Epidermal or dermal | Treat the cause, photoprotect, then topicals and conservative laser | Scrubbing, further inflammation |
Which lasers reach the dermis, and how is treatment ordered?
Treatment for Hori's naevus uses lasers whose wavelength penetrates to the dermis and is absorbed by melanin, delivered in short pulses so that pigment is fragmented with limited heating of the surrounding skin. The 1064 nm neodymium:YAG wavelength, in Q-switched nanosecond or picosecond form, is the mainstay in the published literature because it passes through epidermal melanin with comparatively little absorption and reaches dermal pigment. Shorter wavelengths such as 532 nm are absorbed largely in the epidermis and suit surface pigment rather than this condition. Here, laser for dermal pigment is delivered on platforms described on the pico laser page, which also sets out how settings are chosen for Fitzpatrick III to V skin.
The order of treatment is the order of risk. First, the diagnosis is confirmed and any coexisting melasma is identified, because melasma is heat-sensitive and treating the two as one condition tends to darken the melasma. Second, sun protection and, where melasma is present, its topical control are established before any laser. Third, laser is delivered conservatively in staged visits with review between them, since fragmented dermal pigment is cleared gradually by the body, and the interval is set by how the skin responded rather than by a fixed schedule. A test area may be treated first where the reaction is uncertain. Fourth, photoprotection continues throughout, because new surface pigment is the commonest reason progress stalls.
What are the risks, and who should wait?
The main risk is post-inflammatory hyperpigmentation: brown darkening of the treated skin in the weeks after laser, which is commonly reported in Hori's naevus and is more likely in Fitzpatrick III to V skin, after higher energies, with treatment repeated too soon, or with sun exposure on freshly treated skin. It usually fades with time and strict sun protection, and it is the reason the plan is conservative. Laser over undiagnosed melasma can also provoke a melasma flare, and a report has described melasma appearing after 1064 nm treatment of Hori's naevus. Less commonly there can be pale spots, redness that lingers, blistering or crusting, or a response that falls short of what was hoped. The PIH risk guide explains how settings, intervals and sun exposure govern that risk on Asian skin.
Treatment is deferred with a recent tan or sunburn, with active inflammation or infection on the cheeks, during pregnancy, and while photosensitising medicines are being taken. People with uncontrolled melasma on the same skin are treated for the melasma first. Call the clinic if the treated skin blisters, crusts thickly, becomes increasingly painful or darkens markedly in the weeks after treatment; the complication care page sets out what to do if something feels wrong after a treatment.
What determines the fee, and when should you see a doctor?
Singapore's rules prevent clinics from advertising prices, so this page gives factors rather than figures. The fee depends on what the examination finds, since a face with Hori's naevus alone is planned differently from one with Hori's naevus and melasma together, on the area involved, on the wavelength and mode used, and on how the plan is staged with review. A written quote is given after the consultation, and the fee page explains how quotes are prepared.
See a doctor when grey or grey-brown spots on both cheekbones have not changed with months of pigment creams, when cheek pigment has appeared in adulthood without obvious sun damage, when pigment has darkened after a laser elsewhere, or when a single spot is new, irregular or changing, which needs a dermatoscope examination to exclude something else. At the consultation Dr Sin Yong examines the pigment in daylight, under a Wood's lamp and with a dermatoscope, names each type present, and explains the options including no laser at all. The consultation process page describes what to expect.
