The four photo-biological reactions you will encounter as laser therapist

Photo-biological reactions are the interactions between light and biological material (tissue). What happens when the light energy is absorbed by tissue?

The four most common types of photo-biological reactions you will encounter during aesthetic laser treatments are: photothermal reactions, photoablative reactions, photochemical reactions and photoacoustic reactions.

A photothermal reaction is when the light energy is converted into heat. For the aesthetic treatments based on photothermal reactions, it is not the light that is responsible for the results, but the heat generated from the light.

Most common example of this is laser hair removal. The light is absorbed by melanin and then converted to heat. This heat dissipates to the surrounding tissue where it is responsible for the destruction of the dermal papilla. Most vascular and pigmentation treatments also fall in this category.

Photoablative reactions are mostly associated with CO2 or Erbium:YAG skin peels. During this type of treatments the light is absorbed by the water molecules in the top layer of the skin. Because of the high energy contained in the laser beam and short pulse length the water molecule evaporates and in the proses ablate the top layer of the skin.

Due to water being the primary target and the abundance of water in the skin, you have an extremely limited penetration depth.

Photochemical reactions are caused by very low-energy levels. It is the activation or deactivation of biochemical pathways present in the body. The most common reaction you will encounter is the stimulation of adenosine triphosphate (ATP).

Photons of the correct wavelength have a direct working on the electron chain in the mitochondria, which leads to the increased production of ATP. Biomodulation is also well known in would healing and sports injury rehabilitation.

Important to remember with biomodulation is that very little energy is required and a too high level of energy will lead to a decrease in effectiveness.

Photoacoustic reactions are the magic behind laser tattoo removal. This is when an extreme short and energy rich pulse causes an acoustic explosion. The ink molecule is then broken-up into smaller pieces that the lymph system can remove in the weeks following the treatment.

Due to the extreme short pulse duration, there is no time for heat to build up and transfer to surrounding tissue.

Have you wondered what the most suitable wavelength is for the treatments you want to do?

The wavelength is often taken out of context in marketing material when you look at equipment. The most important function of the wavelength is that it determines the target (or you can also say that the target determines the wavelength). This means that the wavelength determines the types of treatment(s) that can be performed with a specific machine.

For this reason you never get a machine that can do everything.

The depth of the target molecule will determine the penetration depth for the laser energy. If your target is water, the energy will not penetrate the skin at all, because the epidermis already contains a lot of water.

However, this is not that simple. The penetration depth is influenced by various parameters.

Before you choose a machine or wavelength, you need to know which molecule(s) you should aim for to achieve an optimal result. At the same time you must know how to deal with unwanted absorption. A well-known example of this is the protection of the epidermis during laser hair removal. The target, melanin, is present in the epidermis and in the hair itself. For safe and effective results you need to heat the melanin in the hair, but at the same time you have to ensure that the melanin in the epidermis remains at a low temperature.

Wavelengths for hair removal.

Effective absorption of melanin – the main hair chromophore – occurs within the range between 600-1100 nm. Wavelengths below 600 nm are strongly absorbed by micro-blood vessels and therefore cannot be used for hair removal; Wavelengths above 1400 nm are strongly absorbed by water in the tissue.

Wavelengths for ablative lasers.

Ablative lasers such as CO2 and Er:YAG focus on water as the primary target molecule and are therefore in a wavelength range above 2000 nm.

Wavelengths for tattoo removal.

When you are dealing with tattoo removal, you will also have to look at different wavelengths to achieve good results on different colours.

Modern tattoo removal use Q-switched and picosecond lasers. The three most common wavelengths are: Nd:YAG; Ruby and Alexandrite.

Nd:YAG (532nm) Ruby (694nm) Alexandrite (755nm) Nd:YAG (1064nm)
Red ink Orange ink Purple ink Tan ink Blue ink Sky blue ink Black ink Green ink Violet ink Black ink Blue ink
Black ink Dark blue ink Brown ink

Do NOT attempt tattoo removal with an IPL or long pulse laser, as this can lead to severe skin damage.

How to choose a machine – part two

In this article we will look at some practical points that are important to keep in mind when you look at equipment to purchase. It is of utmost importance that you fully understand the treatment parameters relevant to the treatments you want to do with the machine to enable an informed decision.

The first question, is a triple wavelength diode laser handpiece better for hair removal than a single wavelength diode laser? For background info you can have a look at a previous article, Triple wavelength diode laser hand-piece: marketing gimmick or advanced technology?

The short answer is that a single wavelength handpiece is the better option. A manufacturer can only optimize for one wavelength in the handpiece. Thus, you will be best served with a single wavelength.

Secondly, is the build-in cooling sufficient. You need to know if you’re looking at active build-in cooling to protect the epidermis during treatment. Or build-in cooling to cool the various components of the machine during operation. It must be clearly stipulated that the machine has active skin cooling.

The build-in active cooling is usually not sufficient on its own. To transfer the heat from the skin to the contact part and then to the cold water, one requires time. Most therapists work at a higher pace than what the cooling needs to be effective and therefore you probably need a second cooling source. This can be in the form of a cooling device like an air blower, or ice packs. If you have a look at the article “Working with gel“, you will understand why cooling gel is an ineffective option.

With hair removal specifically, you need a longer pulse length. In the article, The importance of pulse length, you will find that you need a minimum pulse length to ensure permanent hair removal. The thermal damage time (TDT) for hair is between 200 ms and 400 ms. Thus, you need to look for a machine that can at the very least keep a pulse going for 200 ms, but preferably much longer.

For tattoo removal the pulse length is just as important. But here you have to remember that 1 nanosecond is the same as 1000 picoseconds. If a manufacturer calls his machine a pico laser, the pulse length must be less than 1000 picoseconds. Else it is a nanosecond laser, just presented as a picosecond laser. Especially Chinese manufacturers love to do this. 2000 picoseconds = 2 nanoseconds.

It is very important to remember that with the increase in energy you will not get a linear increase in results. What I mean with this is that you may treat a tattoo at 600 mJ and have no reaction and lift it 800 mJ and still have no reaction. But, when you lift it to 850 mJ you suddenly have quite a reaction. The same can be said for other types of treatments. Therefore, it is best to make small incremental changes in energy when you’re not familiar with the equipment or how the client reacts.

For hair removal you will usually refer to fluence, J/cm2, and not power, W. If a manufacturer only states power, W, or joules, J, you should ask yourself what it is he tries to hide. This is usually the case with less expensive entry-level equipment. It is expensive to build a machine that has the capability to deliver high energy (J) in a reasonable time (power, W) on a workable surface (cm2). And one or more of these parameters are usually disappointing with an inexpensive machine.

The high-end machines for tattoo removal will be 2 or more Joule. It is unreasonable to expect any satisfactory results from a machine with 1 or less Joule. Thus, a machine that can only go up to 1000 mJ.

With tattoo removal it is also important to keep in mind that you will lose a lot of energy when you use a dye handpiece. It may sound interesting to you to have multiple dye handpieces for your machine, but be realistic in your expectations on the results you will achieve with such handpieces.

Most manufacturers nowadays have a range for each model of machine they manufacture. With this I mean that you can choose between different energy settings and handpieces and more. It has become very common to provide a prospective client with the top of the range specifications and then use vague language like, it can go up to …, or it starts from…

Make sure that you get the exact specifications of the unit you will be buying. There is a huge difference between a machine that can go up to 20 J/cm2 or one that can go to 50 J/cm2. And are we comparing it with the same handpiece?

If it is a good deal today, it will still be a good deal tomorrow. Be very careful with sales people that try to force a decision. This does not mean that I recommend to you to be indecisive and procrastinate over a buying decision. But it does mean that it is reasonable to take the time necessary to make an informed decision and discuss it with people you trust and know about the topic.

How to choose a machine – part one

One of the most common questions we get at LaserCollege is; which machine must I buy? This question does not have a short answer. Even if it is not your first machine you’re buying, it remains a challenge to get it right. In this article we will explore some steps you need to take to arrive at an answer for this question.

The equipment you use in your clinic or salon are tools you need to achieve a certain outcome. Keep in mind that your expected outcome and that of your clients are not the same. Therefore, you cannot base your decision of equipment on client expectation. To arrive at the point where you know which equipment will suite you best, we usually propose some mind exercises.

The first thing you need to do is to sit down and think of the end result you want to achieve with your clinic, salon or spa. Imagine that you have completed the project and your clinic is running exactly as you want it. Write down in your journal how the perfect day at work went.

Make a description of the physical location, what does it look like and how do you feel while you wonder in your mind’s eye through your clinic? You’re greeting your first client for the day, what is the interaction like? What does the client say about the previous treatment? What are her expectations for this and the coming treatments? In the afternoon you decide to have something to eat in a place close to your clinic and while you’re there you overheard someone talking about your clinic (she recommended it to her friend), what did she say?

When, you have this final picture of where you’re going to in your head it is easier to make a list of the treatments you want to provide in your clinic. Remember, these treatments will bring you to your final destination. When you have a list of treatments you want to provide, you are ready to start looking at the tools you will need for this.

At this point you get on the internet and start looking at machines that will the best suite your needs. The only thing is that half an hour later you’re totally overwhelmed and everything you thought you knew went straight out the window.

If you are a first-time buyer, the best thing you can do at this point is to increase your technical knowledge on both treatments and equipment. The money you spend at this stage on appropriate training will be saved in tenfold when you start buying equipment.

If you are not a first-time buyer, sit down and think about the previous machines you’ve owned. Draw two columns on a page, one for pro’s and one for con’s. Write the make and model (or the name) of your last machine on top and then start to list everything you liked about that machine under pro’s. Also include things that turned out well for you with this machine that you did not expect. Under the cons you list everything that irritated you about the machine and problems you’ve experienced that you do not want a repeat of. Do this exercise for every machine you have owned.

If you’ve previously owned machines, think about the people / companies that supplied you. Have you built a good relationship with your suppliers and have they served you well? What changes in this relationship will make an improvement for you? If you had an unpleasant experience with a supplier, what can you do to prevent a repeat of it?

If it is your first machine you want to purchase, think about any high-ticket transaction you’ve made before, like the purchase of a vehicle or property. What was good about those suppliers / agents and what not?

After you’ve completed all the above exercises, you are almost ready to purchase a machine. The last piece of the puzzle is your technical knowledge. You need to fully understand the treatment parameters relevant to the treatments you want to do. When you know and understand treatment parameters you are ready to decide on a machine.

Next time we will look at some promises that distributors and manufacturers make in their marketing material. What does it really mean to you and how you’ll be able to know if it’s true or not?

Biomodulation for male-pattern baldness

Androgenetic alopecia, or also known as male-pattern baldness, is a common disorder affecting 50% of men over the age of 40 and 75% of women over the age of 65 worldwide. Baldness is a stressful experience for both sexes, but substantially more distressing for women.

Biomodulation is often offered as a possible solution to androgenetic alopecia. But, is it really effective and how does it work?

Low energy light therapy has been used for this type of treatments and various medical studies are available on the subject. The efficiency has been demonstrated repeatedly over many years.

The question now is, how does it work?

From a paper published in 2013, Low-Level Laser (Light) Therapy (LLLT) for Treatment of Hair Loss; Pinar Avci, MD, Gaurav K. Gupta, MD, PhD, et al. We learn that:

“Laser phototherapy is assumed to stimulate anagen re-entry in telogen hair follicles, prolong duration of anagen phase, increase rates of proliferation in active anagen hair follicles and to prevent premature catagen development. The exact mechanism of action of LLLT in hair growth is not known; however, several mechanisms have been proposed. Evidence suggests that LLLT acts on the mitochondria and may alter cell metabolism through photodissociation of inhibitory nitric oxide (NO) from cytochrome c oxidase (CCO) (Unit IV in the respiratory chain of mitochondria), causing increased ATP production, modulation of reactive oxygen species, and induction of transcription factors such as nuclear factor kappa B, and hypoxia-inducible factor-1. These transcription factors in return cause protein synthesis that triggers further effects down-stream, such as increased cell proliferation and migration, alteration in the levels of cytokines, growth factors and inflammatory mediators, and increased tissue oxygenation. Moreover, NO is known to be a potent vasodilator via its effect on cyclic guanine monophosphate production and it can be speculated that LLLT may cause photodissociation of NO not only from CCO but also from intracellular stores such as nitrosylated forms of both hemoglobin and myoglobin leading to vasodilation and increased blood flow which was reported in several studies. Yamazaki and coworkers observed an upregulation of hepatocyte growth factor (HGF) and HGF activator expression following irradiation of the backs of Sprague Dawley rats with linear polarized infrared laser.”

In more digestible English, it means that biomodulation extend the active growth phase and prevents premature activation of the resting phase. It is also possible to cause terminalization of vellus hairs, producing terminal hair growth.

The key here is to start treatment as early as possible when increased hair loss and thinning is noticed and keep with it over an extended period. It can take up to 3 months of regular treatment before visible results appear.

Most studies on hair growth used lasers or LED’s in the visible red spectrum ranging between 620 nm to 660 nm. Using fluence ranging between 5 mW/cm2 to 100 mW/cm2.

Treatments are usually well tolerated and are often described as relaxing. A treatment course can be started with three treatments per week and then reduced as results become visible. A continues maintenance of one treatment per week is recommended.

How to use the Fitzpatrick scale questionnaire

According to Wikipedia; the Fitzpatrick skin type scale was developed in 1975 by Thomas Fitzpatrick as a way to estimate the response of different types of skin to ultraviolet (UV) light. It was initially developed on the basis of skin colour to measure the correct dose of UVA for PUVA therapy, and when the initial testing based only on hair and eye colour resulted in too high UVA doses for some, it was altered to include the patient’s reports of how their skin responds to the sun; it was also extended to a wider range of skin types.

Nowadays the Fitzpatrick scale is the standard instrument to evaluate a client’s skin before laser or light-based therapy. However, it seems that a lot of therapists have a problem with interpreting the Fitzpatrick scale. The main reason for this is that the terms used to describe the skin are subjective and with that the fact that we do not remain constant on the scale throughout our lives. It is possible to move a level up or down for the majority of people falling between type 2 and 4.

The Fitzpatrick scale questionnaire is recommended as one of the best ways to determine the skin type of client. It remains still recommended combining it with a second verification, especially for therapists with less experience.

How to use the Fitzpatrick scale questionnaire:
The questionnaire consists of two sets of questions; genetic disposition and reaction to sun. For each question you have to allocate a value between 0 and 4 for that question. At the end of the questionnaire you add up the various values to get a grand total.

The Fitzpatrick scale questionnaire.

Generic disposition

Score 0 1 2 3 4
Your eye colour? Light blue, grey, green Blue, grey or green Hazel or light brown Dark brown Brownish black
Natural colour of hair? Sandy, red Blond Chestnut / Dark blond Dark brown Black
Colour of non-exposed skin? Reddish Very pale Pale with beige tint Light brown Dark brown
Do you have freckles on unexposed areas? Many Several Few Incidental None

Reaction to sun exposure

Score 0 1 2 3 4
What happens when you stay in the sun too long? Painful redness, blistering, peeling Blistering, followed by peeling Burn sometimes, followed by peeling Rarely burns Never burns
To what degree de you turn brown? Hardly or not at all Light colour tan Reasonable tan Tans easily Turns dark brown quickly
Do you turn brown within several hours after sun exposure? Never Seldom Sometimes Often Always
How does your face react to the sun? Very sensitive Sensitive Normal Very resistant Never had a problem

Add up the total scores for each section for your skin type score to give you a better evaluation of your skin type.

Genetic disposition ____

Reaction to sun exposure ____

Total skin type score ____

Total skin type score Fitzpatrick Skin type
0 to 6 Type 1
7 to 13 Type 2
14 to 20 Type 3
21 to 27 Type 4
28 to 34 Type 5
35 and over Type 6

Verification question: Which of the following best describes your skin type?

Description Type
Always burn, never tan 1
Always burn, sometimes tan 2
Sometimes burn, tan somewhat 3
Rarely burn, tan with ease 4
Moderately pigmented, tans very easily 5
Deeply pigmented, never burn 6

Working with gel

Using gel during a treatment is in itself neither good nor bad. Using gel under a misguidance of what it actually does, inevitably leads to a negative effect in your results. The greatest benefit in the use of gel during a laser or light treatment is that it enables the applicator to glide more smoothly over the skin.

Using a gel as coolant for epidermal protection is not the most efficient epidermal protection you can offer your client. Skin cooling during a photothermal treatment is required to remove the heat from the epidermis. This is best accomplished by active cooling. It can be in the form of a water or air-based skin cooler, or even an ice pack. Using this type of skin cooling allows for the heat to be extracted and removed from the epidermis. An alternative is also cryogenic cooling. With this method of cooling, the skin is cooled right before and after it is heated.

Using gel as skin cooler does not allow for the heat to be removed. It creates a layer on top of the skin where the heat can conduct to. But then it is locked into the gel layer. As the treatment continues more and more heat is locked into the gel layer, causing an overall increase of epidermal temperature. This process can be reversed if you combine gel with a form of active skin cooling.

Another reason why therapist believe in the necessity of gel, is for conductance. This is an idea derive from technologies like ultrasound and micro-current, where conduction is of the utmost importance. With light therapy, absorption of the light is of the utmost importance. Any barrier between the applicator and the skin (or target) can have a negative influence on absorption.
The gel layer reflects and refracts the light. Depending on the wavelength and gel used, it can also absorb some energy.

To conclude, if you are using gel it is best to use the thinnest possible layer of gel to ensure minimal interference with your treatment results. If you use active skin cooling in combination with gel, it is important to remember that you still need to allow time for the cooling to be effective. If you have an applicator with build-in skin cooling that you glide over the skin on gel, you need to allow more time for a given area to be cooled sufficiently.

COVID-19: Round two

Looking around me, I see an everyday street scene. Pretty much similar to every other year before. It seems that most people around started to believe that the whole COVID-19 pandemic is something from the past. People are relieved to be out again, to be able to interact with others again.

Two weeks later, and we suddenly have a return of the pandemic with a vengeance. From one day on the other politicians don’t want to do television interviews any more and the blame-game for unpreparedness is starting all over. So, what is the biggest thing that we’ve lost during this small grace period we had? Our naïvety.

We no longer have a lag of experience on what it takes to keep the statistics reasonable. We no longer have a blind believe that it’s only going to be for a short period that we have to stick it through and it will become OK again. My question is what does it mean to me as an aesthetic clinic owner.

The whole collective thinking that kept us going through the first wave was, that in the not too distant future it will return to normal. Now, it becomes clear that it is not going to return to normal. It’s going to stabilize at something that is still unknown. So, how do I prepare myself and my business for this ride ahead?

I want to start with a little lesson that I’ve learned in my life so far. What ever happens, it’s not nearly as bad as the media wants you to believe. We all look up to the media to keep us informed, but it has one big fault. The media is also busy selling something, mostly advertising, and good news does not sell nearly as well as bad news. Therefore, stay informed, but don’t dwell on public opinions. Find a way for yourself to be able to make an objective judgement on how things are going. It doesn’t matter how simple it is, it just has to anchor you in times of uncertainty.

At present my biggest challenge is how do I redefine value? If we’re facing a two-year period where physical contact and close distance to other people are discourage at all cost, what is the real service that I will be delivering to my clients? Does this service consist of one or more components?

The depth and richness of the service we provide to our clients will become more meaning full. If you have focused on treatments only and have not introduced some retailing in your clinic, how will you accommodate the reduced treatments? But, it is not just about selling products. Do you provide your client with something unique? Does the client really has a reason to come to you, or can the supermarket provide the same or even superior value?

What the supermarkets are wonderful with, are options and choice. Unfortunately, a lot of therapists think that it is what they also have to offer. If options and choice are the only things you have to offer your clients, you do not have anything more to offer than the nearest supermarket.

Do you have specialized knowledge that you can apply to reach a decision? Knowledge is worth nothing, applied knowledge is priceless. The one thing that the world needs at this point in time is courageous people who are willing to apply their knowledge to arrive at decisions. As we are more and more flooded by a sea of options and choice the more we have need of firm decisions. When, you have the capability to guide your client in the decision-making process you have more value to offer than most others. The question now is how do you apply this in everyday life?

You start by getting to know your clients and understand their needs and preferences. Only then can you help your client to make a decision that benefit her most. The easier way to introduce this into your clinic is to start with your 20% top clients. The clients responsible for the most net profit in your business. Learn to provide these clients with an true client experience and you may find that this group may be sufficient to carry you through turbulent times.

Triple wavelength diode laser hand-piece: marketing gimmick or advanced technology?

All of a sudden triple wavelength diode laser hand-pieces seems to be the greatest advancement in hair removal laser for the decade. But is it truth or trickery? The arguments are logical and not easy to disproof. Thus, for most it seems to be the latest advancement in hair removal lasers.

Since it takes years to make an accurate evaluation of a new technology, it is still too early to talk from experience. But what we can do is to look at science and model the latest and greatest on our existing body of collective knowledge. And based on the outcome of these models we can make some predictions.

The first thing we will look at is the actual mechanical working of combining three different diodes in one hand-piece. This is possible as we all know, but does it come with a price we prefer not to know? One of the greatest challenges when building a diode laser is controlling residual heat. This is the heat that a diode generates and that remains in the hand-piece from the process of turning energy from electricity into light energy. This heat is one of the main threads to the life of a diode and a manufacturer has to optimize the machine’s internal cooling system to get rid of this heat.

The residual heat created, differ between different wavelength diodes. Building a three wavelength hand-piece, a manufacturer can optimize for one of the wavelengths and not all three. Thus, two of the diodes will not be optimized. Some manufacturers will go for a 50%, 25%, 25% distribution between the wavelengths, indicating that the system has been optimized for the 50% wavelength. Other manufacturers will go for a 33,3%, 33,3%, 33,3% distribution, indicating that either one or none of the wavelengths has been optimized for.

The prediction we can make from this knowledge is that a system that has been optimized for a specific diode, like a single wavelength hand-piece will be more stable and outperform a system that has been partly optimized. Thus, the chance of a single wavelength hand-piece breaking is much lower than that of a triple wavelength, the productive lifetime of this single wavelength system will also be significantly longer. But this is purely technical and only relates to the machine.

The flip side of the coin for having the benefits of three wavelengths, is that you also have the drawbacks of three wavelengths. What I mean with this is that you as therapist can no longer optimize your treatment protocol to improve results to the extent that you can when working with a single wavelength. Do you have a dark skin type? Although you have 50% Nd:YAG in your hand-piece, you are actually governed by the 25% Alexandrite Thus, you have to reduce the energy to a level where you protect the epidermis against the shortest wavelength of your system.

The melanin absorption coefficient differ almost with a factor ten between 755 nm and 1064 nm. It means that if you reduce the melanin absorption at 755 nm by 1, you reduce the melanin absorption at 1064 nm by 10. If you have a 755 nm (25%), 810 nm (25%) and 1064 nm (50%) hand-piece and reduce the fluence from 10 J/cm2 to 9 J/cm2 (10% reduction), you will greatly reduce the melanin absorption for the greatest part of your machine’s output. The effect of 755 nm will reduce to 97% of what it was, the effect of 1064 nm will reduce to 50% of what it was.

Working with a single wavelength hand-piece, you can optimize your treatment protocol for that wavelength. Working with a triple wavelength hand-piece means that you have to optimize your treatment protocol for the wavelength that forms the highest risk to your client, even if it is the smallest percentage of your output.

The prediction here is that when you work with a multi-wavelength hand-piece you will not be able to optimize for hair removal, but you will be forced to optimize for skin protection. This means that you will get better hair removal results with a single wavelength hand-piece.

Coming back to our initial question: marketing gimmick or advanced technology? I believe that triple wavelength diode hand-pieces for laser hair removal is a marketing gimmick. I do not say that you will have no results with a triple wavelength hand-piece. What I do say is that you will have inferior results with a triple wavelength system if directly compared to an equivalent single wavelength system, and even then operator competence will be the determining factor.

Skin resurfacing with Er:Glass vs Er:YAG

In a 2015 study: “A Prospective, Randomized, Double-Blind Comparison of an Ablative Fractional 2940-nm Erbium-Doped Yttrium Aluminum Garnet Laser With a Nonablative Fractional 1550-nm Erbium-Doped Glass Laser for the Treatment of Photoaged Asian Skin”. Found the researchers that:

Reductions in pigmentation and uneven tone/erythema scores were significantly greater after Er:YAG, while wrinkle score reduction was significantly greater after Er:glass. Physician and patient assessments for the overall features showed greater improvement in the Er:glass. Treatment-related pain or adverse events were less in the Er:YAG.

Let’s start by looking at the difference between the two wavelengths. Er:Glass at 1550 nm and Er:YAG at 2940 nm.

At 1550 nm the water absorption coefficient is 1/2000 of that of 2940 nm. We also find some melanin absorption at 1550 nm which is no longer present at 2940 nm and there is still some haemoglobin absorption at 1550 nm what also is not present at 2940 nm.

What does this mean in practice? At 1550 nm you still have a photothermal reaction, where you have a photoablative reaction at 2940 nm.

What happens with Er:Glass fractional, is that you create small ‘wells’/’tunnels’ in the skin where you coagulate and evaporate the tissue. These ‘wells’ can range from 400 μm (micrometer) to 1,4 mm (depending on various factors). The average thickness of the epidermis is 0.1 mm or 100 μm.

Er:YAG has very little penetration depth compared to Er:Glass, about 50 µm (depending on various factors) per pulse. But unlike with Er:Glass where you are more limited in the amount of passes you can go over an area during a treatment, with Er:YAG you can increase the passes. This makes Er:YAG more suitable for problems in the epidermis, like pigmentation. Whereas Er:Glass is more suitable for deeper laying problems, like rhytids.

Keep in mind that you can ablate with an Er:YAG as deep as you can treat with an Er:Glass. But with a fractionated machine this is not very practical to do. With a full ablative Er:YAG machine you will have no limitation on ablation depth, since you just keep doing passes until you reach the required depth.

A combination fractional treatment of Er:Glass and Er:YAG is actually the ideal for impressive anti-ageing and skin rejuvenation results without extended recovery time. Although, each of the wavelengths on its own will also not disappoint.