has a red raw bottom

He's never had a really bad case of nappy rash before...sometimes it gets a little pink or spotty but clears up overnight with the help of some sudocrem or booby juice. This however has been there since Saturday afternoon and is getting worse. I've tried Gaia skin soothing cream, sudocrem, breastmilk and canestan all to no avail. He's been without a nappy pretty much all day but it's a really angry red rash, not spotty at all just raw and patchy looking (like a few layers of skin have come off iykwim?)

Could it be a reaction to something he ate? I've never seen a rash like this on him before. The only thing out of the ordinary I can think of that he ate was a jar of Heinz baby food, the 'organic' one, he has jar food once in a blue moon and never has had the Heinz brand before. Could there have been an additive in that perhaps that hasn't agreed with him?

I've been cleaning his bottom with water and cotton wool for the past few days rather than wipes is there anything else I can do? A salt bath perhaps?