Never overdo peppermint essential oil.
(Honestly, this is pertinent advice for ALL essential oils.)
I wanted a relaxing, ache relieving bath after a long night out and of course I turned to lavender and peppermint. Which is fine, except that both came in bottles with no pour control, and I was too lazy to go locate my dropper. I assumed it would all be fine seeing as I was in this giant tub of water.
I pour the lavender in, using my eyes to estimate. It's fine. Lavender is actually a relatively mild oil compared to most, and while you should always use caution and dilute by default before applying or ingesting any essential oils, I didn't feel any side effects and was rather basking in the immediate calm it induced.
Then I added the peppermint oil. For a while it was fine, and I was enjoying the mingling of floral and minty relaxing scents, then the cooling tingly sensation spread and that was new, but expected.
What I didn't expect is for that cooling tingly sensation to intensify exponentially and start to feel like a very cold chemical burn, even in the hot water! I wouldn't wish that feeling on my worst enemy.
You see, even in that much water, oil will float (and I knew this but the vast amounts of water had always seemed to help spread the oil around)! The peppermint oil just settled around my skin, wherever near the surface, and coated it every time I moved. Needless to say, when the burning started, I immediately jumped up, drained the water, and started the shower.
I ended up spending quite some time under the shower soaping up and rinsing my skin, over and over till the sensation abated. I also applied olive oil (standard carrier oil) to the worst hit of the skin in hopes of diluting whatever was left of the peppermint essential oil. I did worry about this locking in the peppermint oil and not letting it evaporate but the burning stopped after I did this so that worked out. Also, with the rather vigorous soaping, my skin was dry and tight and was crying out for moisturization so some more oil-based lotion helped out.
I'm writing this about fifteen minutes after all of this, and let me tell you, there are parts of my body STILL feeling that cooling tingly sensation (but no longer burning, thank God)!
All this is to say, DILUTE and NEVER overdo essential oils. Handle with care and be aware that accidents happen so I recommend handling even the bottles in gloves, just in case some spills.
Trust me, you don't want to know what a cold burn feels like.
Lesson learned so you don't have to do it the hard way.