My gelding is prone to it and although he's in a dry clean stall and sand
paddock & arena I find it crops up when he's working harder thus sweating
more, and when I'm hosing/bathing him a lot - generally when I'm riding a
lot. <g> Only seems to occur on the white feet, and I've always treated it
with Panalog (for dogs ears) when bad. I've started using a good anti-fungal
shampoo I got from my vet though and it seems to be under control.