I'VE been thinking about getting my first tattoo. While I haven't settled on a design, I have been doing some reading about the tattooing process.
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And it turns out there is some pretty funky science underneath your ink.
People often think that tattoos involve injecting ink into the skin, where it simply gets trapped. But when you're getting a tattoo and the ink is pushed into your skin, it doesn't just sit there.
Something far cooler, involving your immune system, takes place.
Macrophages are a type of immune cell. I like to think of them as the Pac-Man of the immune world.
They kind of patrol around the body, gobbling up pathogens, bits of cell debris, and anything foreign.
They're attracted to the site of wounds, helping to clear up any invaders and prevent infection.
As tattoo needles injure the skin, macrophages are attracted to the area. They recognise the ink as being foreign, and they go ahead and eat it up.
The ink is then stored within the cells, and they sit there, keeping your tattoo in place.
That's not the end of the story though. Macrophages, like other cells, don't live forever. At some point, those ink-gobbling cells will themselves die off, and the ink that they had captured will once again be released into the skin.
When this happens, new macrophages come along, recognise that ink as foreign, and clean it up. And so the cycle starts all over again. Your tattoo is really the result of a complex cellular dance.
Although tattoos are generally considered to be forever, they can now be removed.
Laser removal attempts to smash up those ink-storing macrophages into tiny pieces, so that our lymphatic system can drain them away. But it takes time and often many treatments - probably because each time a macrophage is killed off, others are swooping in and grabbing some of that ink.
You might have noticed that tattoos tend to fade over time, and this turnover of macrophages might also be partially responsible for that. As one dies and another comes along to re-capture the released ink, some tiny amounts of ink may be lost, drained away in our lymph. And so, over time, the colour becomes less intense.
Humans have been tattooing themselves for thousands of years, and in many areas of the world they have important cultural significance. Tattoos can be beautiful - and so is the science behind them.
Dr Mary McMillan is a senior lecturer at the School of Science and Technology, University of New England.
