Short answer: a hot spot is a sore, inflamed patch of skin. It can get worse fast when a dog keeps licking or chewing it. Your vet should look at it.
What the sources say
PDSA calls this acute moist dermatitis. It says the skin becomes inflamed and infected when it is rubbed, licked or nibbled, and that anything that makes a dog chew or lick one spot can lead to a hot spot. Cornell's page on hot spots also covers them as a vet matter.
What to do
PDSA says it is important to stop your dog licking or scratching the area, even before you see your vet, by using a protective device such as a buster collar or a body suit. Call your vet for treatment and to look for the cause. Do not put creams or home remedies on it unless your vet tells you to. See when a dog refuses the cone and itching and hair loss.
Get the right help
Ask your vet about treatment, and what started it.
This article is general education, not veterinary advice. If your dog seems unwell, is in pain, or something changed suddenly, call your vet. If it could be an emergency, do not wait.
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Sources
Sources & care notes
Frequently asked questions
What is a hot spot?
A sore, inflamed patch of skin, called acute moist dermatitis, that gets worse fast when a dog keeps licking it.
What causes one?
Anything that makes a dog chew or lick one spot, from irritation below the surface to a simple itch.
What should I do first?
Stop the licking and scratching, even before the appointment, with protection such as a buster collar or body suit.
Why call the vet instead of waiting?
Because it can get worse fast, and the treatment should also address what started it.
