Whether it’s biker gangs or bachelorette  parties, a lot of people love to get tattoos.

Nearly a third of people in the US and a quarter of people in the UK have at least  one tattoo. That’s a lot of people.

And getting that sweet body art involves  injecting foreign material into the body, not to mention the teeny puncture wounds  from tiny needles as the ink is injected. This process can cause inflammation, and inflammation means the immune  system is getting involved. But even after the tattoo-induced  inflammation subsides, it looks like that sick dragon on your  back is still affecting your immune cells.

Which could teach us something  about – of all things – vaccination. [♪ INTRO] To know why your immune system is  on the alert when you get a tattoo, we have to talk a little  bit about what tattoos are. The inks are insoluble pigments  suspended in alcohol or water. Those pigments can be natural  or synthetic chemicals.

Sometimes, metal oxides are present. Some of the components in tattoo ink have been known to cause allergic contact dermatitis. In poorly regulated inks,  there can be high levels of certain metals or additives  that aren’t great for you.

Also, tattoos are made of  many tiny injection sites and these can get infected,  if not looked after properly. But let’s go with the best-case scenario: high-quality tattoo ink, injected  under sterile conditions. When you get a tattoo, ink is  microinjected into your dermis, the middle layer of your skin, below the  sheddable skin cells of the epidermis.

Some of that ink gets washed  away to the nearest lymph node, but most of the pigment sticks around. Your body’s “foreign object alert” goes off, recruiting immune cells called  dermal macrophages to check it out. This is your immune system’s job.

There’s no way to say “don’t worry boys, I’m doing this on purpose, so  you can hang back for now.” Besides, given the risks we mentioned earlier, it’s probably good for your immune  cells to get involved just in case. The skin gets inflamed, because immune  system signalling can cause swelling and redness as blood vessels dilate  and immune cells arrive on the scene. But ideally, when those macrophages show up, tattoo ink is the only foreign object around.

These cells swallow the  pigment, but don’t digest it. They stick around, keeping the ink in place. A macrophage doesn’t live forever, but when it dies another macrophage  comes along and re-swallows the ink, so the tattoo stays put.

Unfortunately, tattoo ink isn’t a healthy diet: these macrophages have shorter  lifespans than those that don’t eat ink. So… maintaining a tattoo involves  cycling through dermal macrophages. But how does that affect  the immune system overall?

To test this, in a 2025  study, researchers tattooed mouse footpads with red, black, or green ink. As we’ve mentioned, tattoo inks are not equal: setting aside the lack of  standardization in additives, different colors have different pigments,  hence the team testing three different inks. What they found was that pigments  accumulated in nearby lymph nodes, causing a color-dependent increase in node size, which was still significantly  different two months post-tattoo.

There was also an uptick in the production of immune signalling molecules  immediately post-tattoo, as well as recruitment of  various types of immune cells to the dye-laden lymph node. Basically, the immune system was being vigilant. The immune signals varied in timing  and intensity between dye colors, but all had some long-term effects.

All this got the researchers  interested in how tattooing would affect the immune system’s  responsiveness to vaccination. Vaccines work by giving your body a piece of an infectious agent in advance of infection. Or a dead version, or a genetic recipe, depending on what kind you’re talking about.

In general, though, think of it  like showing your immune cells a mugshot so they can do  a drill of their response. This way, the body can get itself primed  and ready to fight the real invader. Vaccines are often delivered by injection.

And while we already know that  it’s a bad idea to inject a vaccine into a fresh tattoo, or to get a tattoo at  the injection site just after vaccination, it wasn’t clear how vaccines and  tattoos interact more generally. And if you didn’t know that, yeah,  wait at least a month between getting a vaccination and  getting a new shoulder piece. We’ll come back to the new study, but before that, all science needs funding,  so here’s a quick break.

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They’re also giving you unlimited daily access to everything on Brilliant with 20%  off an annual Premium subscription. So in this 2025 study, mice were given a COVID-19 mRNA vaccine 2 days or 2 months after tattooing. And there was an effect: tattooed mice had lower spike presentation on macrophages. mRNA vaccines for COVID-19 deliver  blueprints for a harmless piece of the virus.

In order to work, immune cells like  macrophages have to take up the mRNA, and translate it into the  virus’s so-called spike protein. Then they bring it to some B cells  and go “Yo, get a load of this.” Then the B cells go “Oooooh,  so that’s what it looks like. Cool, I’ve been warned and will be ready to make a bunch of antibodies  for next time it shows up.” But in the mice with tattoos, the “get  a load of this” part was happening less.

Tattooed mice also had reduced production  of the type of antibody known as IgG, and IgG is one of B cells’ go-to weapons. Since their macrophages were already busy, they weren’t expressing the spike protein as well. So they weren’t presenting B  cells with example spike protein, which basically means the vaccine  didn’t work as well in tattooed mice.

And they found that human  immune cells cultured in a dish that were given the mRNA vaccine behaved similarly to the mouse model in the  presence of different tattoo inks. But it’s not all bad news. A different set of mice were  given a UV-inactivated flu virus, a type of vaccine that doesn’t require macrophages to take it up  and make the antigens itself.

In this case, the mice with  tattoos had more robust responses to the vaccine than the control group,  especially those tattooed in red or black. In a way, the tattoo ink had  primed the immune system. We call ingredients that do this adjuvants, and they’re often administered with  vaccines to enhance their effects.

So it looks like the heightened  immune surveillance caused by tattoos could be a good or bad thing  for vaccines, depending on the type. Also, the effects varied depending  on how recent the vaccine was. But that’s not where the  how-has-tattooing-affected-vaccination story ends.

A 2008 study showed that injecting vaccines using a tattoo gun was more effective than  your typical intramuscular injection. Subsequent studies have shown similar results, when it was a DNA-based vaccine being injected. So even if it turns out tattoos  don’t boost some vaccines in humans the way they do in mice,  one day your immune system may still benefit from tattoo technology.

In theory, anyway. Obviously, vaccination wasn’t ever  the intended use of tattoo guns, so researchers have been tweaking the  system to enhance vaccine delivery. Having tattoos could influence how  your body responds to vaccination.

The type of ink and the timing  could make a difference, as could the type of vaccine. Or at least, they do in mouse models,  which are famously not people. More work needs to be done,  especially human studies, to see what the pros and cons are.

Obviously, there’s nowhere near enough evidence to make a recommendation  about tattoos here. But what does seem clear that tattoos  are in a long-term relationship with your immune cells, so it makes  sense they’d affect immune responses. Might not be something you think about  when you’re in the artist’s chair, but it goes to show just how  complicated our bodies are. [♪ OUTRO]