My six month old son has urticaria pigmentosa. Are there any safe topical medications that I can give him?

He is too little for an oral antihistamine, is there anything out there that is mild and safe that can be applied topically?

Talk to a pediatrician first, then a dermatologist if you have to.

There is not a topical medication that I know of. However, as a 6 month old, you should be able to provide him with an oral/liquid antihistamine. Whatever you provide, it won't cure the condition - it might help with the itching but that's about it.
Good Luck!
Your Friendly Dermatologist