I've been noticing for a week that my guinea pig has very red ears and constantly scratches them. I'm not sure if it's an infection, mites, or just that the environment is too hot. The air conditioning at home hasn't been working well lately and it gets extremely hot here in August.
Red ears with constant scratching is almost never just heat, but it doesn't automatically mean mites or infection either - it could be allergies, moisture irritation, or even poor ventilation in the cage. Either way, a vet who knows rodents is the only one who's going to give you a real answer, because you can't diagnose this by eye alone.
Take him to the vet as soon as possible because that's almost always mites or an ear infection, not just heat, and it can get worse fast. In the meantime, lower the temperature in the room as much as you can, make sure your guinea pig has access to fresh water, and check that there aren't any cedar or pine shavings in the cage because that irritates the ears a lot. Red ears with constant scratching aren't something you can just ignore for a couple days - he needs antibiotics or mite treatment depending on what the vet finds.
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