I have skin type IV, and I have read that Erbium is much safer with "darker" individuals than CO2. My question is, How deep can you go with Erbium Laser on a "dark" individuals safely, without risk? (in mm). I understand that it is better to be safe, but please answer honestly. Not suggested depth, but deepest depth.
How Deep Can You Safely Ablate a Darker Individual with a Laser?
Doctor Answers 1
Safe depth of laser treatment in darker skin.
Great question, but complex answer. Erbium/YAG lasers operate in a near-infrared wavelength (2940nm) where the (invisible) laser energy is quite well absorbed by water-containing tissues (skin is one of those tissues). CO2 lasers operate in the far infrared wavelength (10,600nm), where water absorbtion of the laser energy is less. As such, CO2 laser energy penetrates deeper (since less of it is absorbed as it travels through the skin layers) and has a less precise (more thermal) effect.
Thus, erbium lasers are not "safer," their energy is about 20X better absorbed by skin, thereby penetrating much less deeply. CO2 laser energy, by contrast, is less well absorbed, and therefore penetrates more deeply. But the biophysical effects of laser energy depend on more than wavelength alone!
CO2 lasers are typically capable of much higher energy outputs, which is necessary for identical tissue effect compared to better-absorbed (and therefore much more superficial) erbium laser energy. So, there's not only the differential in absorption at each laser's wavelength, there are the differences in laser power, defined as fluence, which is also related to energy delivered per unit area (spot size of the laser). This is why laser output is expressed in energy (Joules) per unit area (J/cm squared). Bigger spot = fixed amount of energy spread over a larger area, or smaller spot for the same amount of energy concentrated on a tinier area (like a magnifying glass in the sun).
Then there are a few other things that happens to laser energy, like reflect off skin that is oily, scattered by non-target chromophores in the skin, and refracted at an angle, thus "missing" the intended target by a tiny amount. Not to mention non-target chromophores (like the melanin in darker skin) absorbing energy.
Also important are the number of "passes" the laser surgeon makes with the laser over each skin area, and whether or not the skin is scrubbed clean and dried prior to the next pass. (That serous blister fluid that seeps from the skin absorbs much of the next pass of erbium laser energy, which is why so many treatments are claimed "ineffective." Erbium energy only removes the uppermost epidermis and very superficial dermis, after which very little or no additional deeper tissue is removed, only the fluid vaporized. Usually in this scenario the doctor "blames" the laser on ineffective treatment, when actually it is operator lack of awareness of these biophysical facts.)
All of this comes down to the experience of the laser surgeon (not appropriate for a technician, IMHO) selecting wavelength (type of laser), power setting, spot size, duration of laser pulse, number of passes, and the inherent absorptive characteristics of each individual's skin.
Lots of variables! (Why expertise is needed, not choice of machine!)
Or asking about how deep can you go (safely, which of course differs with each individual based on the above characteristics).
BTW, we're talking 30-50 microns per pass with the erbium/YAG laser (if dried properly after each pass), and 100 + or - 40 microns per pass with the CO2 laser. And that's for fully ablative lasers; these numbers do not generally apply for the fractional versions of these same laser wavelengths.
So, your answer is not even in mm; it is in microns (1000 per 1mm). Anything deeper (total with all passes) than 500-700 microns may be tempting a scar, particularly if there is any difficulty with wound care during healing. Besides, you can't select a doctor based on what laser s/he uses, and then "find out" how deep they are willing to speculate their treatment might go. Of course, I know you want the most aggressive (safe) treatment possible, so you can get the most result for your buck!
This is potentially dangerous thinking.
Select a laser surgeon with expertise in multiple wavelengths, availability of more than one laser choice (if all you have is a hammer, everything is NOT a nail), and experience, not someone who will use the laser you "read" is "safer" with dark-skin races, and has promised to try for just shy of a nuclear wasteland on your skin!
For more information, please click on the web reference link below. Best wishes! Dr. Tholen
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