All EO's are not the same. Some you can use in higher amounts, some irritate if you use too much. What EO's were you thinking of using?
Check out IFRA's website (
http://www.ifraorg.org/GuideLines.asp) and Martin Watt's Plant Aromatics. IFRA has information on some essential oils and essential oil components. Watt's publication includes information from IFRA and has a section specifically on safety. It's available in the US through Anatolian Treasures (
http://www.av-at.com/plantaromaticsavnp.html). To get an idea of the kind of info he has, go to his website, too (
http://www.aromamedical.com/).
I would also check out this book. Essential Oil Safety: "A Guide for Health Care Professionals", by Robert Tisserand.