Homeopathy is based on a rule of nature called the Law of Similars. This law states that "like cures like," or that a medicine can cure a sick person if it can cause a similar sickness in a healthy person. For instance, if you peel an onion, your eyes burn, itch and water. You might also have a runny nose and begin to sneeze. If you had similar symptoms during a cold or allergy attack, such as a runny nose, watery eyes and sneezing, a homeopathic micro-dose of the remedy Allium cepa (red onion) would help your body heal itself.