Cats are curious about everything except citrus fruits. Even the smell of citrus can send cats scurrying in the opposite direction. The response is actually a defense mechanism, as citrus fruits can sicken cats if eaten.
Citrus fruits contain limonin, volatile oils and large amounts of acid, all of which cats find offensive.
Ingesting citrus fruits can cause cats to experience gastrointestinal discomfort, vomiting and diarrhea. Excessive amounts would need to be consumed for truly severe reactions. Fortunately, most cats will naturally avoid citrus on their own.
Lemons, limes, oranges and grapefruits should all be kept away from cats.
All citrus fruit parts, including the flesh, peel and seeds, can be harmful to cats.
Strong citrus scents can be used to curb many bad behaviors in cats. Citrus fruit peels and sprays will keep cats off furniture, out of houseplants and away from gardens.