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This could certainly be a hot spot but it could also be an allergic reaction.
Hot spots happen when there is an abrasion or scratch on the skin. Even flea bites and tick bites can start it. Then the abrasion gets wet or moist and bacteria takes over.
To treat a hot spot, you need to shave the area completely. Then wash the spot with peroxide or a betadine solution. Then apply some antibiotic ointment.
If it doesn't help, you are dealing with something more, like allergies to fleas or the environment, and you need to see your vet.
Let me know if you still have questions.