Tattoos are permanent because the ink granules are deposited into the dermis and are generally too large for the immune system to eliminate. The body binds the ink between dermal cells and largely abandons it.
In 1981, Drs. Anderson and Parish published the Principal of Selective Photo Thermolysis (“SPT”). SPT works because some things absorb laser light frequencies better than others. Applying laser energy for a short time will only damage the things that absorb the light best. Small particles like tattoo ink granules should be treated with very high energy in nanosecond pulses at the laser frequencies they selectively absorb. That sparked the race for tattoo removal lasers and the development of fast "Q-Switched" lasers.
The first Q-Switched tattoo removal laser was the Ruby Laser (650 nm frequency). It worked well but damaged skin. The Ruby was replaced by the Alexandrite 755nm laser. 755 nm is gentler but destroys skin pigmentation and occasionally scars. Finally, the Nd:YAG 1064/532 nm was born and quickly became the industry standard.
Nd:YAG removes tattoos with little to no damage to the skin or its natural pigmentation. Darker skins could finally be treated safely. While frequencies became safer, pulse durations got shorter, beam uniformity improved and power increased. Higher laser power provided wider beams (spot size) that reduce unwanted heating and shortened treatment time from 20-30 minutes to less then 10 seconds. Those are the reasons that modern tattoo removal is safer, more effective and more comfortable than in the past.
Q-Switched lasers remove tattoos by photo acoustic (shake and break) effect. The laser works by rapidly heating and cooling the ink causing the particles to fracture. The cycle happens in fewer than 10 nanoseconds, faster than heat can transfer to surrounding tissue (20-50 nanoseconds). The ink fragments are consumed by macrophages and transported away by the body's natural immune system. Thus the tattoo fades.
Conventional removals at Zapatat generally take 8-15 treatments and ART (R20) lessens the visits by half or more. The interval between conventional treatments is 6-8 weeks and the ART (R20) is 10-12 weeks. The exact period depends on the effectiveness of the body’s immune system, skin color and how the skin and tattoo react to laser treatment. The total time and treatment number varies. Because there are so many controllable and uncontrollable variables, the laser operator’s skill is very important. Given the identical laser, the more skilled and experienced operator will give better results in fewer treatments with the least side-effects and discomfort.