One essential oil that you can actually ingest is oregano oil. A study done by the US Department of Agriculture found that oregano oil is strong enough to kill off salmonella, so you can imagine that it's likely to help fight off everyday germs, too. Park suggests taking two to three drops of a diluted oil a day throughout the course of your cold. "Make sure to have a glass of water handy to wash it down," she said. "It's not the tastiest oil in the world!"