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.
For both humans and cats, the over-the-counter medication Benadryl can treat more than just allergies. The side effects of Benadryl can help ease other conditions. Even in humans, the active ingredient in Benadryl is used to calm the nerves. As always, consult your veterinarian before giving your cat human medication.