Allergic Reaction Under The Head Of His Penis.Treatment?

My boyfriend is having an allergic reaction under the head of his penis and part way down its shaft. It just started after having intercourse while I am using the NuvaRing. We know he and I are both clean so it must be from the ring. We need to know how to clear him up. I will obviously use a different form of contraception but in the mean time what should he use to get his penis back to normal?