Tattoos are formed of particles than can also be stuck together in clumps. If the particle or clump of particles is larger than around 0.02mm ( 2 hundredths of a millimeter) they will be too large to be removed by the macrophages. Actually breaking the particles down to this size is not too difficult which is one reason why initial treatments produce good results.
However even when broken down to digestible sizes many particles will not be removed for one of the following reasons :
- They have been ingested by a fibroblast which is resident in the skin
- They have been ingested by a macrophage that is unable to move
- They are trapped between cells
With each treatment some of the particles are broken down further and fibroblast cells containing pigment can become moribund and potentially removed by a macrophage, which will have the effect of fading the tattoo. Alternatively they can be reabsorbed by a new fibroblast, in which case the pigment will remain in situ but instead of a single particle it will be several more dispersed particles and will also tend to fade the appearance of the tattoo.
The problem is that as the particles become smaller the power of the laser needed to shatter them increases. If we try to reduce the size further with a relatively low power laser what we end up doing is basically cooking the skin which is painful and can result in scarring and pigment changes.
Ideally we want to deliver a very fast pulse of energy so that the tiny, highly energy absorbent tattoo particles, are heated very quickly but the surrounding skin is not. Slower lasers simply cannot deliver the energy fast enough and if the operator tries to push the machine beyond what it is capable of the patient suffers pain, potential scarring and pigment changes.