Healthy dogs shake their heads during routine hygiene practices, such as shaking off water, parasites and debris. Dogs also shake their heads in response to the discomfort or pain associated with an illness or injury.
In the absence of the usual stimuli of water from a bath or swim, parasites such as fleas and ticks, and debris including dirt and dander, dogs shake their heads as a way to shake off pain and discomfort. The most common condition that can cause a dog to shake its head is an ear infection. Other conditions can include an object lodged in the ear canal, insect bites, physical injury and allergic reactions. Symptoms that can accompany the head shaking include foul odor emanating from the ears or other affected area of the head, redness or swelling, excessive scratching, and sensitivity to routine touching or examination.