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Goodness poor Ryder! That looks to be a very large hot spot. It would be best to have him seen today. If you can’t the entire area needs to be shaved down. Some dogs need to be sedated because it’s so painful. Once the hair is removed cleaning is easier and the area dries out. I prescribe oral antibiotics, steroids or apoquel, and a topical spray. The hot spot tends to heal with in 5 days. So if you can shave it great then clean it with a mild soap and water. Dry well. Trying to clean it with the fur still there will just trap moisture.