Why the gentler laser clears sun damage better
Commentary: Are Deeper Laser Treatments Advantageous in Treating Solar Dysplasia?
Sun spots live in the outermost layer of skin, so a laser that removes that whole layer ought to clear them best. In practice it does not. A non-ablative wavelength that penetrates twenty times less shallowly gets comparable or better clearance, with a fraction of the downtime — and the interesting question is why.
Four numbers worth knowing
What we found
The logic says deeper should be better, and the logic is wrong.
Solar keratoses are confined to the epidermis on histology, so removing the entire epidermis ought to give the highest clearance. Early fully ablative resurfacing reported clearances of 92–100%, which seemed to confirm it.
Later evidence brought ablative lasers back to the pack.
More recent studies put remission after fully ablative and deep fractional ablative treatment at 44–80% — on par with 5-fluorouracil, and in most cases inferior to photodynamic therapy.
A wavelength that barely scratches the surface performs comparably.
1927 nm thulium is non-ablative: it preserves the stratum corneum. Its chromophore is water, but with ten times lower affinity than ablative lasers, so it penetrates 150–250 microns against roughly 4,000 for short-pulse CO₂. In a 24-participant study, facial solar keratoses fell by 91.3%, 87.3% and 86.6% at one, three and six months.
Pushing the density high costs remarkably little.
On-label densities for this wavelength run to 70%. Our group has used super-dense settings of 92–94%, which add only 36 to 48 hours of downtime, and sustained solar keratosis clearance of up to 85% at six months.
The skin barrier survives, and that is why healing is quick.
Even at those densities and power settings the stratum corneum is preserved, with laser-induced change confined to the epidermis and upper papillary dermis. Keeping the barrier intact reduces infection, poor healing and subsequent scarring, and markedly accelerates recovery.
The limiting factor may be deeper than any laser safely reaches.
Ultraviolet mutations occur in the epidermis and in the epithelium lining hair follicles. Those adnexal structures sit well below the safe depth of even powerful ablative lasers, so what determines lasting clearance may be the burden of dysplasia down there rather than how completely the surface layer was destroyed — which would explain why removing more of the surface does not help.
A plausible mechanism is an indirect one.
The proposed explanation is a bystander effect: the wavelength provokes a cytokine response in neighbouring keratinocytes already undergoing involution, setting off an apoptotic cascade that may reach adnexal structures deep in the reticular dermis. It would also account for the dermal remodelling and improvement in redness that clinicians observe but that the superficial histology does not predict.
What this means for you
Downtime is not a proxy for effectiveness
The assumption that a harder treatment must work better is the exact assumption this commentary sets out to unsettle. For sun damage specifically, the gentler wavelength holds its own.
Ablative lasers still have their indication
For solar elastosis and deep wrinkles, fully ablative resurfacing gives excellent aesthetic results. The argument here is narrower: it is about clearing solar keratoses, not about abandoning ablative treatment.
Expect to need maintenance
Every field treatment for sun damage is followed by recurrence, because the ultraviolet mutations that drive it sit in the follicles as well as the surface. Treatment manages an ongoing process; it does not end it.
Why this matters
There is a persistent assumption in laser medicine — among patients and clinicians both — that a more aggressive treatment must produce a better result. For sun-damaged skin that assumption does not survive contact with the evidence, and it leads people towards downtime and risk they do not need.
This commentary was written to set out the comparison plainly and to be honest about what is still not understood. We can show that the superficial wavelength performs at least as well; we cannot yet fully explain why, and the piece says so rather than dressing up a theory as a finding.
Why it matters to you
If you have been told that clearing sun damage requires a deep, aggressive laser and a fortnight indoors, that is worth a second opinion. For solar keratoses specifically, a gentler wavelength achieves comparable clearance and you are presentable far sooner.
What this study cannot tell you
Every study has a boundary, and it is fairer to state it than to leave you to guess.
- This is a commentary, not a study. It argues a position from published evidence and clinical experience rather than reporting new controlled data.
- The high-density protocol described is this group's own clinical experience, not a published trial with a control arm.
- The proposed bystander mechanism is explicitly offered as a theory. It has not been demonstrated.
- Clearance figures come from studies with differing protocols and follow-up, so they should not be read as head-to-head comparisons.
- All field treatments for sun damage are followed by recurrence; none of these figures should be taken as permanent clearance.
Questions people actually ask
Do I need an aggressive laser to clear sun spots?
For solar keratoses, the evidence does not support that. A non-ablative 1927 nm wavelength, which penetrates around twenty times less deeply than an ablative laser, has produced clearance rates that are comparable or better.
Aggressive ablative resurfacing remains excellent for deep wrinkles and sun-related textural change — that is a different problem with a different answer.
How much downtime does the higher-density treatment add?
Taking the density from the usual on-label maximum of 70% up to 92–94% adds roughly 36 to 48 hours.
Because the outer barrier layer of the skin is preserved even at those settings, healing stays quick and the risks of infection and scarring stay low.
Why does the gentler laser work as well?
Nobody fully knows, and the commentary says so rather than pretending otherwise. The leading theory is an indirect one — that the wavelength triggers a signalling response in neighbouring cells which causes damaged cells to die off, including some sitting deeper than the laser itself reaches.
It would also explain the improvement in redness and skin quality that clinicians see but that the shallow histology does not predict.
Will the sun damage come back?
Some of it will. The mutations that cause solar keratoses sit in the epidermis and also in the lining of hair follicles, which are deeper than any of these treatments safely reach.
That is true of every field treatment, not just laser, and it is why sun damage is managed over time rather than cleared once.
Cite this paper
Lim D. Commentary: Are Deeper Laser Treatments Advantageous in Treating Solar Dysplasia?. Opinions and Progress in Cosmetic Dermatology. 2021;1(3):48–49.
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Published 2021 · Summary written and reviewed by Dr Davin Lim, FACD · General information, not personal medical advice.
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