Can sunblock be used for poison ivy?

No: There's nothing in it that will treat poison ivy. If you put it on before you go in the woods it may help keep some of the plant oil off you that triggers poison ivy but i doubt it will do much to protect you.

Dr Brown agreed

Don't add problems : Not likely to help it, but since skin is already inflamed and that person has already demonstrated a tendency for chemical skin sensitization, contact dermatitis, putting sunblock on the affected skin could increase the chance of becoming sensitive to a chemical in the sunblock.