It could be a few things...one is ringworm which as you know being a nurse, can be transmitted to humans..the another is a hotspot or moist dermatitis which is the keys where its highly humid, is a possiblity...lastly is a spider/bug bite but he would probably be itching that. I would try and keep it clean and dry and you can try using Lotrimin cream and see if it helps. It will take a couple weeks to see improvement but it shouldn't worsen if thats what it is. If it goes away with the cream then it may be ringworm. I would be sure to wash well after touching the area just in case. Should it get bigger or worsen then a vet visit is needed.
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