Melasma vs. ABNOM vs. PUL: Why Telling Them Apart Before Treatment Matters

Not every brown patch on your face is melasma. Melasma, ABNOM (Acquired Bilateral Nevus of Ota-like Macules), and PUL (Partial Unilateral Lentiginosis) sit at different depths in the skin and stem from different causes — so treating all three with the same laser approach can lead to different outcomes. You may never have heard of ABNOM or PUL, but in clinic we diagnose them nearly as often as melasma.

Why does diagnosis come before pigment treatment?

Because when the diagnosis changes, everything changes — the laser wavelength, the energy settings, even how far apart your sessions are spaced. Each condition places its pigment at a different depth. In melasma, overactive melanocytes and a damaged basement membrane work together, leaving pigment chronically scattered through both the epidermis and the dermis. In ABNOM, the melanocytes live in the dermis itself. PUL, by contrast, is a pigmented lesion of the basal layer of the epidermis, and it shows up on one side of the face rather than both. Different causes mean different responses to treatment — and if the lesion is misdiagnosed, laser treatment can actually make it worse.

Many patients tell me they’ve sat through laser toning session after laser toning session with nothing to show for it. When that happens, I start from scratch: skin imaging first, then a fresh diagnosis. Among people who come in for facial pigmentation, a significant number either don’t have melasma at all or have melasma mixed with other lesions on the same face. Some have kept repeating gentle laser toning, convinced their ABNOM or PUL was melasma.

What exactly are melasma, ABNOM, and PUL?

Melasma shows up as brown patches with soft, blurry borders spreading symmetrically across both cheeks. It’s most common in women in their 20s to 40s and develops from a mix of factors, including UV exposure and hormonal changes. It’s chronic and prone to relapse — not something a few sessions will clear.

ABNOM is a lesion where the melanocytes sit in the dermis rather than the epidermis. That deeper position is why it looks bluish-brown or grayish-brown instead of plain brown, appearing as clusters of small, round spots over both cheekbones. It mostly appears in Asian women from their 20s or 30s onward, and because it develops in adulthood, it’s a separate condition from congenital nevus of Ota.

PUL is a pigmentary condition in which freckle-like brown spots cluster on just one side of the face, never crossing the midline. It usually starts in childhood and is easily confused with other conditions, such as nevus spilus.

How can I tell them apart in the mirror?

Check four things. Does the border fade softly into the surrounding skin, or could you trace it with a pen? Is the color brown or blue-gray? Does it appear on both sides, or is it concentrated on one? And when did it first show up? Blurry-edged brown patches sitting symmetrically on both cheeks point toward melasma. Clusters of blue-gray spots over both cheekbones point toward ABNOM. Spots grouped on one side only, stopping at the midline, suggest PUL.

That said, a mirror check is only a starting point. Plenty of people have melasma and ABNOM overlapping on the same face, and real lesions rarely look as textbook-perfect as the photos. Before any treatment plan is built, a board-certified dermatologist needs to confirm how deep the pigment actually sits — using tools like a Wood’s lamp or dermoscopy.

How does treatment change depending on the diagnosis?

Four factors set the course: how deep the pigment sits, whether the surrounding skin is damaged, how likely the condition is to come back, and how reactive your skin is.

Melasma is a chronic condition with no known cure at present. Laser treatment centers on low-fluence toning, and treatments that improve the dermal environment — pico toning or radiofrequency devices, for example — can help as well. The standard of care doesn’t lean on lasers alone; it combines them with sun protection and topical medication, adding oral medication when needed. ABNOM calls for relatively higher-intensity treatment with wavelengths that reach the dermis, spaced out with generous intervals and careful management of any pigmentation that develops between sessions. PUL takes a two-part approach: darker, well-defined lesions get higher-power laser settings, while lesions with deeper pigment involvement are treated with multiple rounds of low-fluence laser toning. PUL doesn’t demand the long-term commitment melasma does, but it still needs consistent care. I’ll walk through each of these treatments in detail in future posts.

Whatever the lesion turns out to be, I always follow an accurate diagnosis with a one-on-one consultation to talk you through the treatment approach and the expected number of sessions. That’s where we confirm the precise diagnosis, check for any coexisting conditions, and map out the anticipated timeline. Even with the same diagnosis, plans vary with each person’s skin, and results differ from person to person.

What can I expect after treatment, and what should I watch for?

Pigment doesn’t vanish the moment treatment ends. It lightens gradually over one to two months, with results building session by session. Melasma can come back after treatment when UV exposure or hormonal shifts trigger it, so maintenance — sun protection included — is part of the treatment itself. With ABNOM and PUL, diligent sun protection after every session matters just as much.

It’s worth knowing the possible side effects up front. After laser treatment, post-inflammatory hyperpigmentation (PIH) can make the area look temporarily darker, and studies have reported hyperpigmentation in a certain proportion of patients after laser treatment of dermal pigment. To lower that risk, I adjust treatment intervals and provide aftercare guidance covering soothing care and sun protection. Even when pigmentation does appear, it fades with time. You may also notice temporary redness from skin irritation, and that too settles quickly.

Frequently Asked Questions

Can melasma and ABNOM appear together on the same face?

Yes — I regularly see patients with both lesions overlapping around the cheekbones. In those cases, the balance and sequencing of gentler and stronger treatments have to be planned with care. Since it’s hard to tell with the naked eye whether both are present, skin imaging is needed to confirm.

I’ve had more than 10 toning sessions with no results. What should I do?

Before repeating another session, the diagnosis should be re-examined. If the pigment sits in the dermis — as it does with ABNOM — there’s a limit to what epidermis-targeted, low-fluence toning can accomplish. I’d recommend confirming the pigment depth with a Wood’s lamp or dermoscopy, then building a new treatment plan from there.

How is PUL (Partial Unilateral Lentiginosis) different from freckles?

The spots themselves look similar; the distribution gives it away. Freckles scatter across both sides of the face, while PUL clusters on one side only and never crosses the midline. PUL also typically begins in childhood, so looking at both the pattern and the timing helps tell the two apart.

Can pigment look darker after ABNOM treatment?

Yes. In response to the laser, the skin can develop temporary redness followed by post-inflammatory hyperpigmentation. Adjusting treatment intervals and staying strict about sun protection can reduce the risk, though how much varies with each person’s skin. Most cases fade with time, but if the darkening lingers, have it evaluated at the clinic.

Can pico toning alone get rid of melasma?

Melasma is a chronic condition with no curative treatment at present, so pico toning on its own is unlikely to eliminate it. Lasers are used alongside sun protection and topical medication, with oral medication added when needed. The long-term goal is less about “erasing” melasma and more about keeping it faded and well controlled.

Related Reading

• Pigmentation & Melasma Treatment Guide
• Meet Our Medical Team

To book a pigment diagnosis consultation at BASE Dermatology Clinic in Centum City, Haeundae, Busan, reach out below.

• Contact Us

This information is not a substitute for a medical diagnosis. An accurate diagnosis and treatment plan can only be determined after consultation with a board-certified dermatologist.

References

• Update on Melasma-Part II: Treatment
• Comparison of the Efficacy of 1064- and 730-nm Picosecond Lasers for Acquired Dermal Melanocytosis
• Efficacy and Safety of 730-nm Picosecond Laser for the Treatment of Acquired Bilateral Nevus of Ota-like Macules
• Partial Unilateral Lentiginosis: A Systematic Review of 159 Reported Cases and Diagnostic Considerations

This content is for medical information only and does not replace diagnosis or treatment. Results and responses may vary by individual.