Garlic prevents colds & Indian curries kill cold germs. I have grown up on curries from 6 months old & don't eat vegetables & get sick about once every two years. I'm in my fifties & heathier than all my veggy eating friends.
I don't think so but it can loosen up mucous that is clogging your nose. You'll still have a cold but it can temporarily alleviate some symptoms. If you eat it on a regular basis it can speed up your metabolism and help you get over it faster so in that sense it does help. Cayenne pepper is a natural stimulant.