Kissa

Another cause of this pain can be scar tissue problems, it could be the case that the artist has gone too deep into the tissue itself as Shawnna indicated. I would honestly bet on that more than anything, well outside of some possible nerve damage, but nerves generally run much deeper than the depth of the longest needles.

I would ask if your son has ever had problems in the past with any type of scars or scarring pain. If so then there is your answer and not much can be done other than to completely remove the tattoo surgically, which may not in the long run, fix the problem anyhow.

I wouldn't go back to the shop, I instead would see a doctor, the "shop" will never admit to any wrong doing nor be medically qualified to determine what the problem is. Many shops in fact do not have legal liscense's or have the liscensing but not always qualified artists (I've been working with "artists" for for well over 20 years).
Some artists are so fresh they don't realize how deep they are going or forget to tighten their needles at a proper depth and check on regular basis, especially when doing large pieces.

I have 6 tatoo's and even a hand made one, not one of them hurt post 2 weeks. I do have one in particular that does raise itself up from the skin now and then, a very weird but rare phenominon, but it's completely harmeless.

I would also ask or wonder if possibly it wasn't the tattoo that was the source of the issue but maybe something in and of the shoulder itself. Again, this is why I'd really suggest he see a family doctor at the very least to rule this out.

- Barbie
"cheap tattoos are not good, good tattoos are not cheap"