Diagnosing and treating itchy pets is a tall order, writes veterinarian Lyssa Alexander, who explains the many causes of itchy skin in pets. Some pets have only mildly itchy skin, while others are so irritated that it affects their quality of life. In many cases, an underlying allergy is to blame, according to Alexander. Allergies in pets are numerous and include environmental allergies, flea allergies and food allergies. Other causes of itching include mite and ringworm infections or systemic or immune diseases.