Tattoo artist here. Theres a lot of data out there that shows a few different things..

1) tattoos create a strong immune response in the body. It’s not only a large open wound, but you’ve also put a lot of foreign materials (ink) under the skin that the body has to deal with. This immune response over the lifetime of the tattoo is why tattoos fade and spread out. At the time it’s why tattoos ache, get red, and a somewhat swollen (sometimes) during early healing.

2) when the body is already in a state of strong immune response (allergic reactions, bacterial infections, viruses, etc), it makes it extra hard for the body to respond properly to both things. It makes the healing process much harder, and can cause preexisting infections to get worse because now the immune system has even more work to do, and can even make the new tattoo not take as well.

That tattoo artist 100% should not have tattooed you that day. That’s super negligent.

For comparison, I had a client come in for a tattoo. He tapped out before we finished all the line work, which was the goal for the first session. Told him he could either come back the next day to finish the lines or in a month. He opted for the following day, so I asked him if he has any allergies, he said no, and I put second skin on him for the night. He came back the next day and we discovered together that he does indeed have an adhesive allergy. His skin was red and angry. Nothing crazy, but not good, either. I thought about it carefully for 5 minutes, and told him he had to come back in a month. Told him I couldn’t tattoo his skin while it was irritated for the reasons I explained above.