Common symptoms in allergic cats are itchy skin, asthma and respiratory symptoms, acne, sneezing, watery eyes, ear infections, vomiting and diarrhea. If your cat is already suffering from respiratory diseases, environmental allergy often worsens the symptoms. Feline atopy is under-diagnosed, because a common symptom of atopic dermatitis in many cats is over-grooming, which is mistaken for normal behavior or anxiety.