You need a physical block like zinc or titanium oxide, not a chemical block. Neutrogena Pure and Free Baby or there's actually an adult Neutrogena product that's only titanium oxide.

Don't do much with that rash. Aquaphor or plain eucerin to keep it moist once it starts to dry and flake. It will clear up on its own and you don't want to introduce more ingredients for him to react to.

Signed,
Adult with super sensitive skin

Both my kids have the same problem with sunscreen. We have to use the zinc oxide or titanium oxide based sunblocks. Have used the neutrogena baby stick and lotion, vanicream, and a couple others without an issue. You needto reapply more often than the others though.

Oops! Forgot the link!

http://www.amazon.com/Badger-All-Natural-Sunscreen-Unscented/dp/B003II53Z8/ref=sr_1_1?ie=UTF8&qid=1341613279&sr=8-1&keywords=badger+unscented

PP again - here's the 411 on Badger.

Interesting - just last week our DD broke out in a terrible rash all over her chest and back, and we think it is from the California Baby Sensitive Sunblock.

We have used (and continue to use) the Badger unscented (available at Wholefoods) without any problems.