Repeated exposure to low doses of tea tree oil - a common ingredient in many beauty products - can increase a person's risk of suffering from a 'superbug' infection such as MRSA, new Irish research has found.

According to scientists at the University of Ulster, exposure to low doses of the oil can make pathogens such as MRSA, E.coli and salmonella more resistant to antibiotics. As a result, this can lead to more serious infections.

"We have been growing pathogens such as MRSA in low concentrations of tea tree oil. These concentrations are not sufficient to kill the bacteria, but can switch on their defence mechanisms. Unfortunately these defence mechanisms have the added effect of making bacteria more resistant to antibiotics and able to cause 'harder to treat' infections", the scientists said.

Tea tree oil is used commercially in many products, including shampoos, body lotions and toiletries. However there is no legislation requiring manufacturers to state the concentration of the oil in these products.

The scientists point out that this increases the risk that people will use low concentrations of tea tree oil, which fail to kill bacteria, but increase their resistance to antibiotics.

In other words, if a person uses tea tree oil products on their skin repeatedly, any MRSA on their skin could develop increased resistance to the antibiotics which are used to control MRSA infections.

"The bottom line is that tea tree oil should not be used at low concentrations (less than 4%), to make sure that bacteria are killed, not just stressed. Otherwise we are arming the bacteria against treatment by antibiotics", the scientists added.

Details of these findings are published in the Journal of Antimicrobial Chemotherapy.