Anything that irritates the skin and causes a dog to scratch or lick himself can start a hot spot. Hot spots can be caused by allergic reactions, insect, mite or flea bites, poor grooming, underlying ear or skin infections and constant licking and chewing prompted by stress or boredom.
Dogs who are not groomed regularly and have matted, dirty coats can be prone to developing hot spots, as can dogs who swim or who are exposed to rain. Thick-coated, long-haired breeds are most commonly affected.
A simple home remedy for hot spots is Listerine - the original, which is brown! Spray it on the effected area several times a day, and cover the area if possible to keep the dog from licking it. The Listerine may sting the dog a bit, but after several days the area will start to scab over and disappear. Another, very effective treatment is a product called Adams Medicated Hot Spot Spray. It is relatively inexpensive and is available at Walmart!