Skip's had sore patches in summer for a long time, usually controlled by giving him Frontline. This last two years, I've had to keep the Frontline going all year. If I'm late with it one month, he gets a red raw bare patch - or several. Up until very recently, this would heal and the fur grow back once I gave him his Frontline.
The last few months, I've needed to put Sudocrem on any sore patches as well as keeping up with the Frontline, but just recently even that doesn't seem to be keeping on top of it.
So I completely cleared out their pens, removed all straw and dust, laid sand on the floor and wood shavings in their beds.
It's not helped, so I think we'll be off to the vet with him. (They've previously said to just keep on with the Frontline and do it every 28 days, but that's clearly not now working.)