We keep learning.
Fact #1 essential oils and water don't mix--the oils float on top.
Fact #2 Nature's Gift Concentrate and essential oils do mix.

What this means is that when you add essential oils to your bath, they primarily float on top. And this might be the reason why some people feel their skin burns or, in the case of peppermint, feel a freezing sensation. 

To avoid this, try this: In a half cup of warm water, add one cap full of NG 100% or 2 cap fulls of 50% NG concentrate. Then add the amount of essential oil/s of your choice and stir the solution with a chop stick or spoon. Next, add this solution to your bath water.

If you could only tolerate 10 drops of peppermint before, with this approach, it might be much higher. Nevertheless, instead of the oils just floating on top, they will now be dispersed throughout the bath water.

Alternatively, simply add the concentrated NG and the essential oils together in a small container and then add to your bath. and rinse the container in the bath water. 

Try both and see which works best for you.