In 2017, researchers from the European Synchrotron Radiation Facility in France say the chemicals in tattoo ink can travel in the bloodstream and accumulate in the lymph nodes, obstructing their ability to fight infections. However, the authors noted in their paper that most tattooed individuals including the donors analyzed do not suffer from chronic inflammation.
A well-known example is the Nazi practice of forcibly tattooing Nazi concentration camp inmates with identification numbers during The Holocaust as part of the Nazis' identification system, beginning in fall 1941. The Nazis' SS introduced the practice at Auschwitz concentration camp in order to identify the bodies of registered prisoners in the concentration camps. During registration, the Nazis would pierce the outlines of the serial-number digits onto the prisoners' arms. Of the Nazi concentration camps, only Auschwitz put tattoos on inmates. The tattoo was the prisoner's camp number, sometimes with a special symbol added: some Jews had a triangle, and Romani had the letter "Z" (from German Zigeuner for "Gypsy"). In May 1944, the Jewish men received the letters "A" or "B" to indicate particular series of numbers.
Many people start their tattoo sleeves without intent and that's just fine. If you take the organic approach and let one small tattoo turn into another and somehow tie it all together with a background of some sort later, you'll likely have an armful of meaningful body art. Others go full on with a sleeve from the get-go and that works too. Of course, with this approach, you'll be investing a larger sum of money upfront, and you'll need to dedicate the time in the chair to complete the work. Most likely you'll be going back to the same artist which means their schedule will need to be considered as well. If you have the time and the money to complete the job, get it done. Otherwise start a slower and more balanced approach. Never compromise quality for quantity.
The American Academy of Dermatology distinguishes five types of tattoos: traumatic tattoos, also called "natural tattoos", that result from injuries, especially asphalt from road injuries or pencil lead; amateur tattoos; professional tattoos, both via traditional methods and modern tattoo machines; cosmetic tattoos, also known as "permanent makeup"; and medical tattoos.