LO has broken out in hives a few times after having nuts. He has tested positive for all nuts except almonds.

The thing is, he has gotten hives randomly before as well. He has a few around his face right now but didn't eat any nuts or anything new. I'm wondering if it is just related to the cold he has? Or sensitive skin? Or if be touched something at the grocery store and is reacting to it? I'm just debating if I should give him some Benadryl before his nap.