Barney
gets hotspots secondary to his late summer and fall allergies. We use an over the counter product called Domeboro's solution - you add water to it and I dip a cotton ball in the solution and make a compress that I hold on for about 10 minutes and I do it twice a day. It is very effective at catching the hotspot early on and they never get to the point where they ooze or open.
Of course you should only do this after you (1) know what the diagnosis is from a licensed veterinarian and (2) your vet approves of the usage of this product.