Laser treatment in Busan Seomyeon, and how a beam finds one target and not another.

Laser is the treatment category where the same device produces excellent and poor results depending on numbers the patient never sees. Understanding what those numbers do explains why settings matter more than platforms.

Selective photothermolysis

The principle behind every cosmetic laser. Different substances in skin absorb different wavelengths preferentially — melanin absorbs certain bands strongly, haemoglobin others, water others again. Choosing a wavelength that your target absorbs and surrounding tissue does not means energy is deposited where it is wanted and largely ignored elsewhere. That selectivity, rather than aim, is how a laser finds one structure and spares another.

What each target means in practice

Melanin absorption is used for pigment work and lesion removal. Haemoglobin absorption is used for vascular treatment, where the vessel heats and collapses. Water absorption is used for resurfacing, since the tissue itself is mostly water and heating it produces the controlled injury that drives remodelling — see how collagen treatment works.

Why pulse duration matters

Because heat spreads from where it is deposited, and a shorter pulse gives it less time to. A picosecond pulse fragments pigment mechanically with minimal thermal diffusion; a longer pulse heats the target and the tissue around it. On higher Fitzpatrick types that difference is the difference between clearing a spot and provoking post-inflammatory pigmentation — which is why picosecond platforms matter more here than in lighter-skinned markets.

Why fluence is the number that decides risk

Because it is how much energy arrives per unit area. Too little and the target absorbs heat without being destroyed, producing inflammation and no result. Too much and surrounding tissue takes damage it did not need to. The correct fluence sits in a window that narrows as melanin increases, since more of the beam is absorbed by the epidermis before reaching the target — see toning or resurfacing.

Why skin type changes everything

Because melanin is in the way. On Fitzpatrick I skin the epidermis is nearly transparent to the beam; on type IV or V a substantial fraction is absorbed on the way through, heating the surface and reducing what reaches the target. That means lower fluence, longer intervals and a test pass — treating higher types at settings written for lighter skin is the most common cause of laser injury.

Why recent sun exposure is a contraindication

Because a tan is melanin, and the laser cannot distinguish it from target pigment. Treating recently tanned skin means the epidermis absorbs far more than intended, sharply raising burn and pigmentation risk. Four weeks without significant exposure is the standard requirement, and treatment is postponed rather than run at reduced settings — the risk is not linear enough for that compromise — see sun protection.

Why does this category vary so much between clinics?

Because three invisible numbers decide the outcome and none of them appear on a price list. A patient can compare platforms, prices and marketing copy exhaustively and still have no information about wavelength selection, pulse duration or fluence — the variables that determine whether a session clears a spot, does nothing, or causes a mark that takes months to fade. That gap is wider here than for filler or botox, where at least the product name and unit count are quotable, and it is why the assessment matters more than the equipment list.

How does this connect to the other mechanisms?

Lasers deliver the stimulus; the body does the rest. Ablative and fractional treatment provoke exactly the collagen sequence described elsewhere, which is why resurfacing results arrive at three months rather than immediately — see how collagen treatment works. Pigment lasers are the exception, since fragmenting melanin and clearing it is a transport process rather than a rebuilding one, and shows over two to four weeks. Knowing which of the two a treatment is tells you when to look, which is the same question that runs through boosters and lifting alike.

Is a newer machine better?

Sometimes, in specific ways. Picosecond platforms genuinely improved pigment treatment on darker skin. Better cooling improved comfort and reduced epidermal damage. What has not changed is that the operator chooses the settings, and a new platform run at wrong parameters produces worse results than an older one run correctly — see HIFU devices compared for the same argument in another category.

Why fractional delivery works

Because leaving untreated skin between treated columns gives healing somewhere to start from. Full-surface ablation removes the entire epidermis and heals slowly with substantial risk; fractional treatment injures perhaps ten to thirty per cent of the area and the intact tissue between drives repair. That is what made resurfacing practical, and it is why coverage percentage is a setting worth asking about.

What this means when comparing quotes

That platform name alone is insufficient. Two clinics offering the same laser can be delivering different wavelengths, pulse durations, fluences and coverage — which produce genuinely different treatments at the same headline price. Asking which wavelength and what fluence is more informative than asking which brand, and a clinic that answers plainly is describing what you are buying — see how to read a price list.