Common symptoms of feline illness include changes in litterbox habits, changes in appetite and behavioral changes, such as increased vocalization, according to Pet Health Network. Bad breath may also indicate dental problems.
Cats that suddenly start urinating or defecating outside of the litterbox may be ill. In addition, increased urination can be a sign of serious illnesses, such as kidney disease or diabetes, notes Vetstreet. Frequent attempts at urination that do not produce much volume can indicate a blockage, which can be life-threatening.
Other signs of illness may be more obvious. Frequent or prolonged vomiting requires a veterinary visit, according to Vetstreet. Diarrhea or constipation are also cause for concern, especially when combined with vomiting. Although a single cough may not indicate illness, coughing that lasts for a day or more may indicate asthma, respiratory illness or other serious conditions.
Changes in affection levels are another indication that something is wrong, suggests Petfinder. Aloof cats that suddenly become clingy may not be feeling well, while previously affectionate cats may hide or avoid contact. Sick cats may also groom themselves less frequently, while cats in pain or suffering from a skin condition may groom too frequently and cause hair loss or skin irritation. Owners should generally trust their judgment and consult a veterinarian even for very subtle signs, since symptoms can be quite subtle.