Nasty Rash down my left arm

I won't post a picture because it looks sore/unpleasant but if you search for dermatitis online, it's like that, red and bumpy from my elbow to just below my armpit. Not sore, just painful to look at.

Is this a thing with FOLFOX or is 'chemo rash' more of an all over thing? My other culprit would be the weather or a reaction to the wife's ("all natural") moisturiser she put on, but the rash is a larger area than she applied to

I had 4 rounds of chemo absolutely fine but it broke out 2 days after my 5th now I'm worried this might stop them giving me another round next week, or whether I should go in beforehand or what. It's colder weather now and it might just be that but it's weird that it's literally just my left upper arm.