Usually this is the symptom of ticks in one or both ears (Otodectes cynotis). In common language it is called an ear itch.
Ear ticks are so small that one can hardly notice them with an unaided eye. It is possible to see them using a magnifying glass. They look like small whitish spots moving slowly on the surface of an ear duct. While inspection a veterinary surgeon usually uses a compound magnifier, auriscope or an orthoscope.
Ear ticks don't penetrate under the skin and prefer to live and reproduce on its' surface. They feed on dead skin cells and, perhaps, sucking lymph out of vessels that pass through the skin.
Most cats have few ear ticks and feel themselves comfortably, however sometimes ticks cause irritation and inflammation of external ear. In this case a cat constantly shakes ears, scratches and rubs them. Claws may do serious injuries to ears and cause bleeding. If a cat continually scratches skin between ears and areas between ears and eyes, the hairs on auricles may come out, and blood bubbles (hematoma) appear and require a surgical operation, otherwise the auricle will shrink during closing up and will have an ugly look. Aural duct gets inflamed and big amount of dark mutter appears and accumulates inside the auricles in the form of scab.
In most cases ticks are easy to remove by cleaning ears and treating them with the antiparasite medications (generally in the form of drops) during several days. One should treat both ears and (for ticks easily pass onto other animals) all cats and dogs that live in the house should be treated at once, regardless of whether they show any signs of disease or not. One should consult to a vet to take treatment.
Ticks may pass on to another parts of body, so it is not out of place to treat the whole body with powder or an aerosol.
Ear infections and obstruction with sand and dust are more seldom. At that the inflammation may also appear and a cat begins to shake its' head. To determine the real reason, it is better to call for a veterinary surgeon. It is he who will prescribe the necessary treatment.
Translated by Tatiana Karpova (Moscow)
(MSU, Biology faculture, Dep. zoology and ecology).