You can only really feel frequencies below 10,000 Hz.
Essential oils are in the MHz, not sure what you were feeling, unless you were running the one Cerumen that is 320 Hz, which is frankly too low to be an essential oil of any kind.
In order to confirm contact is having a feeling effect, ensure you are running a low frequency, with maximum amplitude, and not using the CS port on the boost.
Warning, this could lead to too much of a feeling. Caution should be exercised when using electricity on the body.
There are settings in place to reduce the likelyhood of feeling low frequencies.
Oh, and the reason you feel anything is because the frequency is able to resonate your muscles and/or nerves.
If it is too high to resonate, no feeling.
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