both my daughters used to get crazy itchy allergic reactions, sometimes we were able to figure out why and other times not, with my one daughter there were already so many meds on board that adding something major was not an option. Many, many times we went with oatmeal baths/packs, which can be done with a washcloth and restrained to certain areas.
Maybe suggest he switch out socks and do some detective work.... see if it is the sock (like perhaps elastic) or if it is the pants (or something else entirely). Having been there and done that with a kid with a major latex allergy, if he is allergic to latex it is nice to know that now and not at some other time when more important things are happening. (once we knew what it was, we were able to avoid it pretty easily).
(I know I am biased from that
experience. If you're like everyone else I know in the northern hem right now it is cold as pluto and it is probably just dry skin itchies)