Carrots are rich in carotenes, which are substances related to vitamin A. They're found in the orange pigments and are good for you, but, if you eat lots and lots of carrots, you can develop a yellowish or orange cast to your skin. It's mostly noticeable on the soles of your feet and the palms of your hands.
Benadryl is another decongestant safe for use in cats, although it is usually not as effective as chlortrimeton in treating congestion. Benadryl is generally more beneficial with treating snake bites, reactions to vaccinations, itching, and insect bites.
Topical solutions containing hydrocortisone offer some relief. They are the most practical in treating localized itching. Cats tend to lick off these preparations. But the use of creams or salves on areas the cat cannot lick, e.g.; top of the head may be useful.