Apparently, the skin reaction thing to tomato and tomato products is very common - something to do with there naturally being histamine in them, which is destroyed to some extent when they are cooked. I don't think it is a true allergy, as you are reacting to the histamine in the tomato rather than producing histamine yourself like you do when you are allergic to a food. Anything more than redness where it has touched the skin - like coughing, wheezing etc might be signs of a true allergy though, so keep an eye out.