Starlighter is right, it's just a case of trial and error. At 1, long sleeved, light coloured vests and light weight combats were our go to for nursery and time in the sum (i.e. covering up rather than putting on suncream).
Sunsense and Green People Organic both flare my son's skin and it's a pretty pricey business (and really uncomfortable for them, poor things).
We find a slightly lower factor suits him better (the blockers in factor 50 have him flared up right away, but a kids 30 works a bit better).
The nivea kids one worked for us last year (not the water proof one!!) but they also seem to change the ingredients year to year so it's always back to the drawing board in Spring!
Good luck finding something that works for you. If you can get the GP to prescribe something you will be lucky - ours has a zero suncream prescribing policy even though my son has ezema & confirmed allergies. We were basically told too bad.
I have a leaflet from eczema society if you want me to pm you it? They recomend trying the following:
E45 Reflective Sunscreen Sun Lotion SPF30
La Roche Posay Anthelios Spray SPF 50
Nivea Sun Children’s Pure & Sensitive Spray SPF50
Soltan Sensitive Hypoallergenic Suncare Lotion SPF 30
SunSense Sensitive SPF 50+
SunSense Ultra SPF 5