To perform a patch test when thinking about using fragrance oils on the skin, start with a low dilution of about 1% and work your way up gradually - but try not to go above 5% if you can. If you experience any sort of reaction to the oil or its constituents, you should terminate use immediately and seek medical advice if required. For those creating scented skin products like creams or body scrubs, it is important to always refer to the IFRA certificate of your chosen fragrance oil to find out how much you should include.