Barking up the wrong tree as an antiseptic?
The Irish Times
Health Supplement, p. 13
24 February 2009
DOES IT WORK? Tea tree oil has been traditionally used to control infection but some studies question its effectiveness
RESISTANCE TO antibiotics is a well-recognised problem. As efforts are made to reduce inappropriate use of antibiotics, other ways to treat infections are being sought.
Many plants contain “essential oils” which have distinctive aromas and can be beneficial for the skin, and some of them also have antimicrobial properties.
Tea tree oil is an essential oil that has been used for centuries to treat bacterial and fungal infections of the skin.
The tea tree is native to Australia and got its common name from British sailors who arrived with Captain James Cook. They used the leaves to make tea, although its taste was extremely bitter. Tea tree oil is sometimes called melaleuca oil based on the plant’s official name, Melaleuca alternifolia.
The British explorers later discovered that the leaves had long been used in Aboriginal medicine to treat wounds. In the 1920s, researchers found that the oil contained the most effective ingredients and this was produced commercially until antibiotics became widely available after the second World War. Recent interest in the oil has developed as part of renewed interest in complementary therapies.
What studies have found
Laboratory studies have shown that tea tree oil is a broad spectrum antimicrobial, active against bacteria, fungi and some viruses. It has been shown to be as effective against antibiotic-resistant bacteria, such as MRSA, as it is against the strains that are not resistant. But all these studies have been in laboratory conditions.
Considerable interest has been expressed in using tea tree oil in handwash formulations as a general antiseptic for healthcare centres. Despite the interest, very little research has been done. One difficulty with studying this area is that the oil is not very water soluble. Many products use alcohol to dissolve the oil, but alcohol itself is an antiseptic. One recent study found that a product containing tea tree oil with alcohol was more effective than soft soap, but the soap was more effective than tea tree oil alone.
Two clinical studies have examined the use of tea tree oil products on people who are positive for MRSA. Conventional antibacterial nasal creams and wound cleansing agents were compared with tea tree oil products and no significant differences were found between the two treatments.
Tea tree oil has also been studied for the treatment of athlete’s foot, a fungal infection. Two studies found that very high concentration solutions (up to 50 per cent tea tree oil) were more effective than placebos, but less effective than conventional antifungal agents.
A variety of products containing tea tree oil are available as acne treatments, mouthwashes and shampoos but what evidence is available does not show that these products have any great advantages.
Tea tree oil is generally safe when applied to the skin, but should not be consumed. Ingesting less than half a teaspoonful has caused severe rashes, confusion and difficulty in walking. In general, essential oils should never be consumed undiluted. Used externally, tea tree oil does not usually cause problems, although it can cause local irritation and allergic reactions in some people.
Care should be taken when applying tea tree oil around broken skin. Several Melaleuca species can be used to make melaleuca oil, but the original tea tree, Melaleuca alternifolia, contains the lowest levels of irritants. Higher quality products should state the species clearly on their labels.
So, while research has confirmed tea tree oil’s antimicrobial activity in the laboratory, the results have not been consistent in practical settings. Conventional antimicrobial agents have been more effective in many studies.
When these fail to work, or have side effects that make their use impractical, tea tree oil may have some benefits.
However, research published earlier this month found some concerning results. The study tested whether tea tree oil combined with different antibiotics was more effective than antibiotics alone against several microbes.
The researchers found reduced effectiveness at all doses against bacteria and yeast. These tests need to be repeated, but suggest that tea tree oil should not be used along with antibiotics.