I take it when you say "st tropez gives me eczema" that you either have eczema and when you have the st tropez tan, this irritates your skin and causes a flare up? or if you havent got eczema any other time it may be contact dermititis caused by something in the solution.
If you have got eczema, I would suggest going to different spray tanners with different solution and ask them to do a patch test where you eczema would be most likely to flare up, ie back of your knees, crease of arm, I am not sure if you had a patch test behind your ear, you would see a reaction to it, but I am not an expert.
Karen