Why do tattoos and PMU fade in patches after laser treatment?

Take a few coloured pencils and one ordinary graphite pencil. Squeeze them tightly in your hand and start drawing something chaotic on a sheet of paper, fast and with pressure, then ease the pressure but keep drawing. You now have a sheet of paper covered in coloured lines of different thickness and intensity.

Now take an eraser and start rubbing these lines out carefully and evenly. The ones drawn with the graphite pencil and light pressure will go first without a trace, then the lines drawn with the same pencil but with heavy pressure will disappear. The pale coloured lines will only get a little lighter, and the dark ones will stay unchanged. All that is left is to rub harder or take a special eraser for coloured pencils.

Do you see the similarity with treating a tattoo with a Q-switched Nd:YAG laser?

Tattoos are also applied unevenly, and the pigment is distributed in the dermis chaotically, at different depths and in clusters of different volume. Accordingly, after a laser removal session, parts of the design also lighten and disappear unevenly.

By the way, the laser also acts on the skin unevenly during treatment: in some places the exposure is insufficient, in others more intense. This happens because of spot overlap during treatment and a slightly changing spot diameter if you work with a handpiece without adjustable spot size and change the focus by varying the distance from the handpiece to the skin.

These two types of unevenness add up and produce different results across the tattoo area.

For example, a small amount of pigment (shading or light fill) combined with intense exposure makes the design disappear quickly, literally in 1–2 sessions.

The opposite situation — a large amount of pigment, for example an outline or a saturated element of the tattoo, combined with relatively weak exposure — gives only a small result. Many sessions are needed, because the changes that occur are minimal.

Do not forget that a laser device gradually wears out, and the power of the pump lamp decreases. The patient's immunity and physiological processes in the skin may fluctuate; add to this the varying distribution of the pigment, its physical and chemical properties, the condition of the skin (whether or not there is scarring) and the different absorption capacity of the ink particles.

The Kirby-Desai scale can help estimate the approximate number of sessions, but it also includes subjective parameters, such as the degree of scarring and the amount of pigment!

I hope it is now clear why predicting the number of sessions and the time needed to remove a tattoo is difficult. Doing it reliably is practically impossible.

When I started doing tattoo removal, I was ashamed to answer "I DON'T KNOW" to a client's question:

"How many sessions does it take to remove a tattoo?"

— Client

Now, with many years of experience behind me and a ton of scientific literature in my head, I calmly answer "I don't know". If needed, I can explain why.

And now a small remark about those who "hold the pencils": professionalism, experience, knowledge of your equipment and techniques, and analytical skills together give greater accuracy in forecasting.

After working with a particular laser for several years and observing the results, you will get a feel for it and understand what it can and cannot do. If you change lasers, you will have to adjust your skills and working methods.

Remember: only after several years of such constant, conscious observation and analysis do you develop the ability to intuitively sense the right settings and approach in each specific case.

Your forecasts become much more accurate. Of course, there is still a chance of error, but conscious observation of a large number of very different situations and analysis of how things change over time give you the level that distinguishes professionals from random people in almost any field!

To become the best, learn from the best. Grow professionally, look for new research data, follow the information shared by professionals. It is a continuous process that will make you number one in your field.