My generally very healthy ( no meds, normal vitals etc) companion who is 77 has had a rash that comes and goes over the last few weeks . We went on cruise for a week and he seemed not to get it then , so we are guessing it is food in our "at home " diet and have been trying to figure out possibilities. I have read that celiac disease sometimes shows this symptom and also have recently seen that soy allergy can cause a coming and going rash. It usually shows up on his buttocks ( mainly) or upper arm and is very itchy and then disappears and shows up again later in the day or the following day. An OTC cortisone cream makes it go away and relieves the itch, but I know whatever is happening outside is happening inside too. We found out that our non dairy creamer has soy and have discontinued it for the last few days and have tried to eliminate all grains from our diet( I realizeall the celiac culprits are hard to always find). I guess my real question is whether it would do any good to see a doctor when the rash is not present for more than an hour or so daily- could any diagnosis be done without the rash presenting at the time? How long after disontinuing a food does it take for an allergic rash to stop? We were on our cruise for a week and it is possible that we were having so much fun that he nevr noticed the rash- but he did comment ( oh, by the way..) when we came back that he didn't remember having it- which is why I think soy and that creamer may be the culprit ( or maybe I'm just hoping as it is easier to avoid soy than the celiac triggers from what I can research.)
Sometimes it's very difficult to find the culprit to which we react... I've been trying for 6 months now with no success! I will say that if I'm otherwise occupied, I'm far less likely to notice my itching (like being on a cruise, lucky you!)
If it continues, you might want to consult an allergist immunologist who can possibly determine what is causing your companion's rash. Normally, they can test for the usual culprits and various food.
Hopefully, you can determine the allergen. Good luck to you.
Did you do anything else different on the trip? Different soap, shampoo, laundry soap, dryer sheets, etc. anything that comes in direct contact with the skin. A lot of skin allergies are from such things. I'd try soap, shampoo, etc that has no dye and no scent for a few days and see if it clears up. An allergist might be able to identify it with testing, but it usually does not cover those types of allergies.
I know that whenever I stray from my old products to try new ones my younger son gets a rash on his belly and/or arms. It usually happens when I try new liquid softners, washing liquids, dryer sheets, or soaps. Sometimes he'll get a rash when he trys a new body wash or those new body sprays (Tag, Axe, etc.) So look and see what you've changed....could even be maybe something like an air freshner or fragrant spray you put on the furniture.