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Why don’t tattoos go away by themselves?

September 16, 2019 / Duncan Fisher
New study, new surprise.

You know that skin cells die and fall off all the time, and are replaced by new cells. We wrote about this continuous cell turnover in detail recently.

The astute reader will now wonder why tattoos don’t gradually disappear. If tattoo ink goes into cells (which it does), why doesn’t the ink disappear after a time, cell-by-cell?

The answer, amazingly, appears to have something to do with the cells that form part of your immune system.

A very recent paper from the Journal of Experimental Medicine1 describes what happens this way:

Ink that comes into your skin arouses the attention of your cellular foreign-body defence system. It helps that the ink comes by needle, because the system recognizes the puncture as a wound, and responds especially enthusiastically. Central to this response is ‘macrophages’. These are a type of white blood cell, whose job it is to gobble up – literally, eat – invaders, like germs, or fungi, or parasites, or anything else that shouldn’t be there. The macrophages consume and then hold onto ink particles.

No cell lives forever, not even mighty macrophages. When ink-laden macrophages finally die, they should release their ink particles.

They do … but then other macrophages gobble it back up. The tattoo stays in your skin. And that’s why. The JEM team watched it happen, in mouse skin, after they chemically killed mouse-macrophages. The ink was just passed along, in a cellular sort of team relay.

Enter, lasers … and targeted toxins?

It’s actually good news, in a way. It means that laser treatment, which does, gradually, help tattoos go away, might get a biochemical boost, now that we know where the ink goes.

Laser light, if the wavelength is chosen carefully, absorbs selectively into tattoo pigments of various colors. There’s no burning, or anything, as people sometimes imagine. But the pigment particles heat up a little, and possibly because of this, break into fragments. Laser light may also change pigment chemistry and cause toxic decomposition of the particles. Whichever way it works, when fragmentation happens, the particles do begin to leave the skin, probably draining through the lymphatic system.

It’s a long process, requiring repeat treatment. But what if, along with laser therapy, the macrophages in the area can be killed, with an antibody toxin similar to what was used in the experimental mice? Wiping out the ink-holding cells, say the team in JEM, then quickly attacking the particles with laser light, does seem like a promising strategy. The trick will be to wipe out the macrophages without doing any harm to the immune system overall.

It’s a very interesting concept, about a very timely issue. We don’t know what will happen next. Your dermatologists will be watching this with great interest.

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