Ear infections are very painful for the pet that suffers from them, and should be treated quickly before they get any worse.
Ear infections (otitis) are inflammations of the ear canal that can be very painful and distressing for the animal. Every species can suffer from them. The ear canal is lined with skin very similar to the outer layer of the skin elsewhere.
That is why some skin conditions turn up in the ears as well.
A range of germs cause ear infections. Besides various bacteria, yeasts (fungi) or parasites can colonise the ear and set off inflammation.
While parasites are common in outdoor cats (Otodectes cynotis, known as ear mites) or in some rodents, in dogs we more regularly find yeasts of the Malassezia spp. type or bacterial ear infections.
Certain habits can also be bad for ear health, such as frequent bathing, which raises the moisture in the canal, or unsuitable cleaning.
Allergies, usually food-related, also lead to ear infections. And some dog breeds are especially prone to trouble in this area (Cocker Spaniels, German Shepherds and so on).
During an ear infection the ear canal is short of oxygen, and certain bacteria that thrive in these conditions multiply. This inflammation leads to an overproduction of wax and, in a bacterial infection, a rather unpleasant smell.
In severe cases, deformities and wart-like growths can develop in the ear canal. As for ear mites, they are tiny parasites, only just visible to the naked eye, lost in the mountain of black wax they produce.
So a cat with large amounts of black deposits in its ears has most likely got ear mites there.
Several signs should alert the owner: if the ear (or both) is red, hot, foul-smelling or has a heavy black or brown discharge; if the animal scratches at the spot, shakes its head, holds the ear differently, or if the ear is swollen or painful. This last point matters, because an undetected and untypical ear infection can still be very painful and may explain, for instance, a sudden bout of aggression with biting.
In all these cases, a visit to your vet is in order.
Ear infections are easy to treat when caught early, though sometimes a sample will need to be taken to culture the germs involved.
In some animals they can keep coming back; a few simple hygiene measures can then help (fewer baths and drying the ears afterwards, periodic cleaning with a suitable astringent, reviewing the type of diet, and so on).