Due to the way in which tattoo equipment operates, there is a level of pain involved. Tattooing needles tipped with ink pierce the skin and leave the ink behind. The needles only pierce under a few layers of skin, but the machine runs very fast and pierces the skin multiple times per second. It is only one's pain threshold that determines how bearable the pain is.
The website Tattoos-hurt.com presents a pain threshold meter that shows the approximate levels of pain regarding each piece of the body being tattooed. According to this scale, the most painful parts of the body to have tattooed are the groin, just under the rib cage, the lower abdomen, the armpits, the nipples and the back of the knees. The site has rated these areas as resulting in levels of pain that may cause one to pass out.
All tattoos result in pain during the tattooing process. Many people can cope with this pain; others cannot. The pain is said to be similar to the feeling of a hot knife or a cat claw cutting shallow lines in the skin. If one is looking for the least painful area to have tattooed, then one should look no further than the outer sides of the upper arm, upper leg or the buttocks.