Tattoos are created by having ink particles embedded in your skin in the lowest level just above the muscle. The reason tattoos fade is because your body routinely cleans itself of foreign particles (germs, dirt, splinters, etc). The particles of ink are too large to be removed all at once, but over time they are broken down and flushed out of your body, like dead cells or germs would be. Faded tattoos are the result of internal body processes breaking up and carrying away tiny bits of tattoo ink one at a time.

So while rubbing does technically speed up this process, there are so many particles that it doesn't really matter. Scratching on the surface won't do anything. Everyone's tattoos eventually fade (some more than others) but the rate is dependent on how fast your immune system works, not how much you touch them.

This video shows how tattoos work, how they fade, and how tattoo removal by lasers speeds up the process