Oregano oil is proven to have anti-parasitic properties, and can fight off bacteria, viruses, fungi and intestinal worms. Oil of oregano can be taken orally in the treatment of arthritis, cold and flu, allergies and sinus pain. The oil may be applied topically to improve a number of skin conditions, including athlete's foot, acne, canker sores and dandruff. Other common ailments treated with oregano oil include warts, ringworm, rosacea, toothaches and insect or spider bites. In addition, oregano oil may be used as a topical insect repellent. Oregano leaves, from which the oil is derived, is often used to treat gastrointestinal issues such as bloat and heartburn. Due to anti-coughing and anti-spasm properties, oregano is used to treat asthma and bronchitis. It may have some effect on rheumatoid arthritis. Urinary tract infections and disorders, as well as menstrual cramping, may be eased by using oregano. The plant is also clinically proven to reduce levels of bad cholesterol and raise levels of good cholesterol.