Why skin becomes more sensitive after laser treatment, and how to care for it

We have previously set out the precautions after radiofrequency treatment separately. The reason we separated that article from this one is that the manner of damage is different.

The principle behind lasers is selective photothermolysis, proposed in 1983. The claim of the original paper is this — if you deliver selectively absorbed light in a sufficiently short pulse, you can damage only the targeted pigmented structures, and there is no need to aim precisely. The optical and thermal properties substitute for target selectivity.

Two combinations were demonstrated — 577 nm at 300 nanoseconds selectively damaged microvessels, and 351 nm at 20 nanoseconds selectively damaged melanosomes.

Here is something we should say honestly. We could not find primary literature directly asserting the contrast that “lasers heat only the target while radiofrequency heats the whole tissue”. It is an explanation that circulates as textbook material, but what can be verified in the original paper goes only as far as the demonstration of those two combinations. And lasers also produce bulk heating — a study of fractional laser in Asian subjects states explicitly that cooling is important to prevent the whole tissue from being heated.

So this article does not use the statement “lasers are safe because they are selective”. What can be verified goes as far as the design principle: “a target is chosen, and a wavelength that target absorbs is used”.

For reference, the correspondence tables often set out — “water at 10,600 nm, melanin at 694 · 755 · 1064 nm, haemoglobin at 532 · 577 · 595 nm” — are also not in the 1983 original paper. They were compiled in later literature and textbooks.

There are two studies following skin parameters after treatment in Korean subjects. Both are in Fitzpatrick IV–V, that is, the usual range of Korean skin colour.

One further thing was established in the 2013 study. The melanin index rose on day 1, returned to normal at one week, then rose significantly again at one month before normalising at three months. That is, the recovery curve is not monotonic. There is a period when it darkens again after having improved once.

The time taken to return to everyday life was also recorded — a mean of 14.6 days (range 4 to 100) in the acne scar group and 17.0 days in the wrinkle group. Look at the fact that the range runs from 4 days to 100. Individual variation is enormous.

So the products you normally use stinging or feeling tight for a few days after treatment is a sign not that the skin has got worse but that the barrier is still recovering. That period differs by site, from one week to one month.

You have probably seen explanations along the lines of “the skin is left open for weeks”. The numbers in the original papers are different.

It may look contradictory that the epidermis closes in a day to a week while barrier parameters take one week to one month. Being covered and functioning properly are different things. It is rather like a roof being on without the building being watertight.

One addition: the flaking that occurs after treatment is sometimes explained as “a good sign that waste is coming out”. What the original paper described is epidermal necrotic debris, and it serves as a route by which melanin is pushed out as well. It comes away by itself within 7 days. Peeling it off forcibly interferes with that process.

The explanation that lasers irritate or damage nerve endings and so make the skin sensitive appears often. We looked for it.

We could not find a single primary empirical study supporting it. No study measuring intraepidermal nerve fibre density or sensory thresholds could be identified. What has actually been measured is only subjective scores for itching · stinging · tightness.

So we explain the phenomenon as “barrier damage → water loss and increased penetration of irritants → stinging · tightness”. This pathway is supported by the measured values in the table above.

This does not mean “the nerve account is wrong”; it means “it has never been tested”.

The most common and genuinely troublesome problem after laser in Asian patients is post-inflammatory hyperpigmentation. We reproduce the figures as they are.

Look at the 75% in the second row. With no preventive measure at all, applying only petrolatum, three in four developed pigmentation. The statement that “pigmentation is rare” does not fit this data.

With non-ablative fractional treatment it is reported lower. In a study in Chinese subjects it was 7.1% to 12.4%. But that study produced an unexpected result.

The high-energy · low-density group was 7.1% and the low-energy · high-density group 12.4% (not a statistically significant difference). That runs in a different direction from the belief that “lowering the output makes it safer”. The authors’ conclusion was that density may matter more. In the same study, the patient who did not receive cooling developed localised pigmentation around the mouth.

The review pooling 14 trials and 313 subjects pointed out one more thing — Fitzpatrick skin type had no significant effect on the occurrence of pigmentation. This may be because most of the subjects in that review were already type III–IV.

The thing most emphasised in laser aftercare is sun protection. In 2026 a network meta-analysis on this subject was published. It pooled 14 randomised trials up to February 2025 and compared several interventions at once.

How should the last row be read?

It does not mean sun protection is unnecessary. Sun protection is the basic premise, but the best current evidence is that it does not by itself prevent pigmentation. What was actually shown to work were interventions a doctor prescribes.

Sunscreens containing anti-inflammatory ingredients have also been tested. In a randomised double-blind split-face trial in 59 subjects who had received picosecond laser, the reduction in pigmentation was greater on the anti-inflammatory sunscreen side, but the difference was not statistically significant.

One caution to add: there is a secondary review describing this trial as showing the sunscreen “more effective”, whereas the original says “no significant difference”. We could not verify the originals of the other figures that review cited either.

A word to add about steroids. There is an explanation that “do not use steroids after laser, they thin the skin”, but the current evidence points the other way. What was used in the trial above was an ultra-short 2-day course, and it halved the pigmentation.

This must, however, be a prescription made on a doctor’s judgement. It is an entirely different matter from applying a steroid ointment you have at home, at your own discretion, for a long period.

This section is the most important in the article. These are also items that appear in our own written instructions.

There is a reason we are setting this table down as it is. Several of these items appear in our own clinic’s post-treatment instructions. Having established that they lack evidence, we need to revise those instructions. But we think the right thing to write is not “there is no evidence, so do not do it” but “this is a conventional recommendation and has never been tested”. Leaving a margin on the side of safety is itself reasonable.

What must not happen, though, is for the two things with solid evidence to be buried under convention. What has actually been shown to work against pigmentation is a short course of steroid on a doctor’s prescription and tranexamic acid. If the advice about ice packs and antibiotic ointment runs longer than the advice about those two, the order has been reversed.

There is a problem reported when low-fluence laser is received frequently: guttate hypopigmentation — pigment dropping out and leaving what look like white spots.

The mechanism has been confirmed histologically. In a study biopsying hypopigmented lesions, melanin was almost completely absent and the number of melanocytes themselves was significantly reduced. Expression of the pigment-producing enzymes was also lowered. The authors’ wording was “spontaneous recovery is rare”.

There is data pointing the other way, so we record it too. In studies cited by a review in a Korean society journal, hypopigmentation was 0% in a group treated with only two passes at low fluence against 17.6% in a high-fluence group. In a study treating 147 subjects at monthly intervals it was 0 of 75.

In other words, it is not toning itself that produces hypopigmentation but cumulative dose and frequency. What the cases above have in common is not the type of treatment but a frequency running from weekly to daily.

These incidence figures are as cited by a review in a Korean society journal, and we could not compare each original abstract directly. So we do not state a percentage flatly, only the direction. Nor could we find quantitative data on rebound pigmentation in Korean subjects.

Reduced to what you should actually observe, in order:

• Using what you were prescribed as directed — the item with the clearest evidence
• Covering — occlusion itself is the standard, not a particular brand
• Sun protection — the basic premise, though it does not prevent pigmentation on its own
• Not pulling the flakes off — they come away by themselves within 7 days
• Leaving an interval before the next treatment — the problems related to repetition came from frequency, not from the type of treatment

And you should know in advance that there may be a period around one month when it looks darker again. In the study of 24 Korean subjects the melanin index returned to normal at one week, then rose again at one month and normalised at three months. Concluding at that point that “it has failed” does not match what is happening.

Written and reviewed by Lee Chi-Hak, MD, medical director of Miso Clinic in Daegu, South Korea. Every study cited above is given together with its design, its size and the limitations the authors themselves recorded, and where we could not find data, we have said that we could not find any.