It is possible to be allergic to tattoos. It's kind of rare but most of the time it comes from red or yellow ink. If you truly suspect allergy from tattoos, your son needs to see a doctor because he may be at risk for anaphylactic shock.

I see this question is old but the answer may save someone's life. i have been a tattoo artist for many years and my wife has been a nurse (rn) just as long so together our opinions hold some merit. go to the doctor or emergency room!!! i have never seen anyone allegic to tattoo ink in all my years. this sounds more like cellulitis: http://en.wikipedia.org/wiki/cellulitis which can be very damaging and hard to get rid of. it takes serious antibiotics which need to be monitored by health professionals. this is not something to be taken lightly!!! i suppose it is possible to be allergic to anything but most likely the problem is a treatable medical condition. btw- many health professionals are going to lecture you about the dangers of getting tattoos but that doesn't mean you won't receive proper treatment, just that you'll have to get an earful of their negative experiences. i would be willing to bet that many of them are doing much worse to themselves every day with sleep deprivation, chemical abuse, elevated stress levels, etc.