Delayed Allergic Response?

Last week I got this interesting letter and photos;

"My tattoo is almost five years old, healed beautifully, hasn't been retouched, and held its colors amazingly well. I never had a problem with it, until September, when I got back from Burning Man. A week or so after I got back, the red outlining on the right side of my tattoo starting itching really bad and I was constantly scratching at it. The left side (both sides are identical) itched also, but not as badly, and didn't end up scarring. I'm still not sure why the reaction happened."

So… what did ookumbubbleoo do take at Burning Man?