Fresh oregano herb
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Oregano is a member of the mint family, along with lemon balm, basil, peppermint, sage, rosemary and thyme. This plant group accounts for over a quarter of the most commonly used herbs. Oregano oil extract is high in essential oils secreted from the underside of the plant's leaves, and has been used traditionally for a variety of medicinal purposes. The oil has been proven in scientific studies to be an effective antimicrobial agent. Study results and expert opinions vary on oregano oil's effectiveness against colds and flu.

Active Compounds

Traditional herbal medicine practices use oregano oil mainly against bacteria, fungi and parasites. There is some anecdotal evidence of its effectiveness against cold and flu viruses, though more studies are needed to confirm these effects, says Richard Stooker, author of the book "Beat the Flu." Oregano oil contains 50 active compounds with immune-boosting and germ-fighting properties, and antioxidants that reduce inflammation. Its nutrient content includes vitamins A and C, both of which support respiratory health and help fight infection. Oregano oil also contains calcium, potassium, zinc, iron, manganese, magnesium, copper and boron.

Ineffective Against Flu

A study published in the June 2004 issue of the "Journal of Agricultural and Food Chemistry" found that oregano oil was ineffective against the influenza virus. In the study, the essential oil inhibited 25 different types of bacteria, 12 kinds of fungi and one type of yeast. One oregano extract used in the study was effective against herpes simplex virus.

Broad Spectrum Effects

Oil of oregano is an excellent broad spectrum antibiotic with warming, drying properties that help heal respiratory and other infections. Aside from its antibacterial properties, this essential oil is useful against viruses and fungi. Colds and flu respond well to oil of oregano, and it is also used for lung conditions such as asthma, pneumonia, whooping cough and tuberculosis, according to Paul Pitchford in his book "Healing with Whole Foods: Asian Traditions and Modern Nutrition." Oregano oil is versatile and can be taken internally in capsule form, or you can add a few drops to a steam bath and inhale the vapors directly.

Respiratory Effects

Oil of oregano helps your lungs recover from a bout with a cold or flu by thinning the mucous, allowing for easier breathing and faster removal of the infecting virus, says naturopath Linda Page in her book "Linda Page's Healthy Healing: A Guide to Self-Healing for Everyone." Oregano oil also has antiviral and antibacterial properties that directly inhibit cold and flu bugs. Page recommends a respiratory detoxification program that uses oregano oil along with other herbs, such as mullein, marshmallow, pleurisy root, wild cherry, ginger and horehound.