Hi Bob
First I like to say I am not  a scientist , nor a doctor of any degree.I am just a regular guy who loves bees, and who uses his God given intuition, with a little common sense. I have been using thyme for about 3 years now, with as far as I know, not having any problems.I use it with my sugar syrup , and as a paraffin wax. In the sugar syrup I boil a cup of hot water, and add 2 to 3 sprigs of thyme , and a tablespoon of Chamomile dried buds. Let it infuse for about five to six hours, strain and pour into a gallon of sugar syrup with a pinch of sea salt. In the paraffin wax I  use beeswax and light mineral oil.(use only food grade mineral oil , you can get this at any pharmacy) Mix it to a soft butter consistency, and add  4 to 5  drops of thyme essential oil. Use this on the bottom of the frame ears, and where it rest. Also on the top & bottom edge of the hive box. You rarely have a problem removing the frames or hive box. The bottom board., I have a Formica sheet that I apply a light mineral oil with 3 to 4 drops of thyme essential oil in it, plus my thyme plants that I have around my hives,and that is all their is Bob.Of course this is my personal view , and I could be way out in left field with this, and some day it will all come crashing   down on me. Time will tell 
George .