Sorry Izzie this site is getting slower and slower on my computer it’s got to be the server change as the rest are fine.
Anyway this sounds like skin-fold pyoderma fold dermatitis it occurs due to rubbing of skin and trapping of moisture in the folds. Pyoderma (bacterial skin infection) commonly develops, almost always caused by Staphylococcus intermedius.
The best way to treat it is topicical with a good residual action wash but with minimal drying or irritating actions (eg. 0.5% chlorhexidine or 2% benzoyl peroxide).
I was once told by a dermatologist the best thing was vinegar but start with 10% vinegar as 100% would be to painful.
Have to say it’s an inherited AI condition very hard to treat and AB do NOT work it will aways come back it has to be treated the old fashioned way topically
Val