Cat allergies
Cats, like humans, can suffer from a wide range of allergies. The most often encountered form of allergy in cats is flea allergy. As cats grow in age, their sensitivity to flea bites grows. Food allergies cover some 5-10% of cat allergies. Food allergies can be recognized through rashes on the skin, itching, vomiting and diarrhea, but these symptoms could occur after ten years as well.

Vomiting
Some cats vomit all the time, while others do so very rarely. One of the most common reasons for vomiting is the removal of fur balls. You should try to brush your cat as often as possible to reduce shedding and the ingestion of hair. If you want to know why your cat vomited, carefully examine the vomit and check if there are any fur balls in there. Fur balls can occur even in cats with short hair.
Another reason for your cat to vomit would be food allergies. You should try to change the brand of food you use and choose one with different ingredients and no food dyes. This could help. Sometimes cats vomit when they have intestinal worms. You should seek your vet for treatment in such cases. Also, vomiting could be a sign of hyperactive thyroid or kidney infection. This is often seen in old cats. The vet could perform some blood tests to see the exact cause.
Diarrhea
If your cat has persistent diarrhea, you could try changing their diet. You could try some boiled rice, some cheese, yogurt, bread or some boiled chicken. Choose something your cat likes. If the symptoms continue for more than two days, you should take your cat to the vet, along with a stool sample. You should call your vet at once if your cat is weakened and refuses to take fluids. Feline urinary syndrome is an inflammation, an irritation and/r an obstruction of the lower urinary tract. Inability to urinate could become a serious problem, potentially fatal, if it is not treated in time. This illness occurs more often among male cats than among females. Your cat could have this illness if it cannot urinate, is urinating blood, often uses the litter box or stops using it altogether.

Diabetes
Diabetes occurs in cats that cannot regulate their blood sugar. Symptoms can include thirst and excessive urination, losing weight or obesity. Usually, this illness occurs in older cats. Diabetic cats need to be kept indoors to avoid accidental feeding that could increase their blood sugar.