Does catnip oil in pet shampoo hurt cats?

It depends on the oil. If a cat ingests a lot of cooking oil such as olive oil, then it is likely it will cause vomiting and diarrhoea. For non-edible oils such as motor oil, seeking immediate veterinary treatment is highly advisable as motor can be incredibly harmful.

If any oil is on the cat, bathe it asap.

However, there are oils that are beneficial in small doses and do not harm the cat at all:

Salmon oil and Evening Primrose oil are two oils that a cat can benefit greatly from. You can also add a weekly treat of oily fish such as sardines or mackerel (best in spring water), or even scraps of plain fatty meat (such as skin from a chicken) either raw or cooked, depending on what your cat prefers as this will have the same effect.

Salmon oil contains omega 3 and omega 6 fatty acids. It is the omega 3 fatty acids that are so valuable in salmon oil. Salmon oil helps improve coat and skin quality and lubricate joints, which an elderly cat may benefit greatly from. It is advisable to use this instead of Cod Liver oil, as this contains a high level of Vitamin A which a cat can overdose on if fed too much.

Evening Primrose oil also contains vitamins and fatty acids that promote healthy supple skin and soft, glossy fur much like Salmon oil.

Both these oils can be found in most health shops and can be added to the cat's meal a couple of times a week. Only a few drops are needed each time.