Common signs of illness in cats include vomiting, diarrhea, loss of appetite and decreased activity, according to WebMD. Changes in urination, coughing, stiffness and skin problems are other indications that a cat is ill.
While it is not unusual for cats to vomit on occasion, a cat that throws up frequently or exhibits symptoms such as lethargy and loss of appetite is probably ill. Vomiting and diarrhea can stem from a number of underlying causes. However, blood in the vomit or feces is typically a sign that a cat is sick, explains WebMD.
Loss of appetite, with or without other symptoms, can quickly become life-threatening. If a cat goes for even a couple of days without eating, it can develop a deadly disease called fatty liver, WebMD reports.
A number of different medical conditions often produce similar symptoms in cats, according to WebMD. Changes in urination sometimes indicate diabetes, a urinary tract infection or bladder stones. Persistent coughing is sometimes related to heart or lung disease. Itchy skin and hair loss are sometimes a sign that the cat has fleas or ear mites, while stiffness or trouble bearing weight may indicate an injury, arthritis or even Lyme disease. Generally, only a veterinarian can determine exactly what is wrong with the cat.