During treatment, the laser beam interacts with the pigment in the tattoo and shatters it into small particles which slowly get scavenged away by cells called macrophages. This action can only be achieved with Q switched lasers delivering nanosecond pulses, such as the Q switched Nd:YAG, Ruby and Alexandrite lasers.
Multiple colors require multiple lasers. The easiest colors to remove are brown and black, the hardest are yellow and green. The more complex the colors are, the more treatment sessions are necessary, varying from 6 to 20 and over. There is never a guarantee that all pigment can be removed. Sessions are repeated every 6 to 8 weeks.
Professional color tattoos are the hardest to remove, because of the number and density of the colors. Professional tattoo artists pride themselves on mixing their own colors, further complicating their removal.
Amateur black tattoos respond the fastest.
Traumatic tattoos involving gravel, gun powder or lead also do very well.
Cosmetic red tattoos such as lip liner and eyebrow liner immediately turn black upon laser impact. They are very difficult to remove.