Eucalyptus: This is a great oil to have on hand if you get frequent colds or suffer from allergies that affect your breathing and make you congested. "Eucalyptus can be used to relieve sore muscles and help clear sinuses,” Scarpelli said. "It also has many antibacterial properties and has been known to stimulate the immune system." Use it in a vaporizer to loosen up a congested chest or apply it diluted to the inside of your nose to relieve nasal congestion. But never ingest it or use it on your skin undiluted, as it can be irritating.