Swelling on partners arm. getting bigger?

The first thing: one thinks about when there localized (just in one spot) swelling is some type of local inflammatory reaction due to a local infection from an infected cut, scrape, insect bite? Swelling could also result for injury/trauma to the area. Rarely would a blood vessel/clot problem be the cause. Especially concerning if associated redness and heat. Probably should see Doc for eval. Good wishes:)