You can have too much of a good thing with Peppermint Essential Oil, as it is one of the essential oils that can be harmful when misused, but it can be a great aid when used knowledgeably.
What is the history of Peppermint Essential Oil?
Peppermint may have originated in the Mediterranean and Northern Africa. For much of its history, Peppermint was used interchangeably with the plain term “mint” and “spearmint,” but scholars believe that the mint mentioned in ancient texts was for Peppermint, which is a naturally occurring hybrid of spearmint and water mint. 
- Egypt: Mint was listed as a calming plant for stomach pains in an ancient Egyptian text, Ebers Papyrus, which dates to 1550 BC. Mint was valued so much in Egypt that it was used as a form of currency.  Dried peppermint leaves which dated to 1000 BC were found in an Egyptian pyramid. 
- Greece: There is a lot of mythology surrounding mint in ancient Greece. Minthe was a river nymph in one of the five rivers of Hades. Hades himself was in the midst of seducing Minthe when his wife Persephone found them, and Persephone vengefully turned Minthe into a low-lying mint plant so people would step on her. Hades was so upset that he gave the plant a sweet, peppery smell so that everyone who walked on her would be able to smell her sweetness, and she would be remembered for her sweet constitution. The Greeks also believed that mint was an aphrodisiac and would not let its soldiers consume it to maintain military control. 
- Rome: The philosophers in Rome were fond of mint and Peppermint, and they wore a crown of mint on their heads to stimulate the mind and soul. Pliny wrote that mint stimulated the appetite. His fellow philosophers Hippocrates and Aristotle believed that mint discouraged sexual behavior, unlike the Greeks.  Royal ambadassadors carried a sprig of mint with them to prevent angry outbursts. 
- Europe: Peppermint was listed as an herbal remedy in the Icelandic Pharmacopoeias in 1240 AD, and it became popular over the following centuries. During the middle ages, monks used Peppermint to polish teeth, and cheese makers used its strong smell to keep rodents out of the storeroom. In 1696, Peppermint was distinguished from mint as its own species. The London Pharmacopoeia of 1721 lists Peppermint as a remedy for colds, headaches, sores, and venereal diseases. 
- North America: The Native Americans of North America had been using a different species of mint native to North America for many centuries before the European settlers came to America. The Europeans brought with them Peppermint and other mints from Europe and they were soon integrated, naturalized, and spread across North America. 
What are the most common types of Peppermint?
Peppermint comes from the family Lamiaceae and the genus Mentha. Mentha contains more than 25 species. 
- Mentha x piperita, or Mentha balsamea Wild
- Naturally occurring hybrid mint crossed between watermint and spearmint
- Indigenous to Middle East and Europe
- Types of Peppermint
- Western Peppermint (Mentha piperita)
- Chinese Peppermint (Mentha haplocalyx, or “Bohe”)
- Both Western and Chinese Peppermint contain menthol and menthone and are considered ancient species
- Varieties of Peppermint
Mentha x piperita Candymint: reddish stems
Mentha x piperita Chocolate mint: flavor similar to Andes Chocolate Mints, and flowers open from bottom up
Mentha x piperita Citrata: Leaves are aromatic and hairless.
- Varities include Grapefruit mint, Eau de Cologne mint, Lemon mint, Orange mint
Mentha x piperita Crispa: wrinkled leaves
Mentha x piperita Lavender mint
Mentha x piperita Lime mint: Leaves smell like limes
Mentha x piperita Variegata: Leaves are green and pale yellow, mottled
Dulgo pole, Bulgarian population #2, Zefir, Clone 11-6-22, Mitcham Digne, Clone 80-121-33, and Mitcham Ribecourt 19 are commercial varities (or cultivars). 
Morocco produces 92% of the world's Peppermint, and Argentina produces 8% of the world's Peppermint. In the U.S., Washington and Oregon are the top-producing states for American production of Peppermint. 
What is an essential oil?
An essential oil is the oil of an aromatic plant which is formed as a “secondary metabolism” of the plant. Secondary metabolisms are natural defense mechanisms which protect the plant from pests and microbials and are either scents, colors, or attractants for pollination. Essential oils can also be called volatile oils. The oil is considered essential because it is the essence of the plant. 
How is Peppermint Essential Oil Made?
Essential oils can be produced through a mechanical expression or a steam distillation. Solvents such as ethanol, acetone, or hexane are sometimes needed for extraction of oils from certain plants.
Essential oils produced through distillation are separated through steam condensation and leaves a small amount of a volatile liquid behind: the essential oil which is extremely concentrated. 
Peppermint loses essential oil if the dry leaves lie in piles or heaps. In an effort to prevent fermentation of the Peppermint, producers often distill the fresh Peppermint immediately after cutting. 
Mint produces the best oil and menthol yield when 10% of the crop is at the flowering stage. It requires a lot of water to grow. The highest oil content is found when Peppermint is harvested in the sun, but if it’s environment is too warm, especially at night, a toxic compound called Menthofuran will form. 
What is peppermint essential oil made of?
Peppermint essential oil contains 1,8-cineole which comprises 3.5-14% of its content. Menthol is the active ingredient and makes up 33-55%, or up to 75% of the plant. 
Menthyl acetate: 2.8-10%
Pulegone: 0.8-24.9% (found in high amounts in young leaves)
a-terpineol: trace-0.4% 
How to Use Peppermint Essential Oil
All essential oils are highly concentrated and they will need to be diluted in carrier oils. Using a diluted essential oil in a carrier oil will minimize the risk of skin irritation. Be sure to use a diluted essential oil blend unless you are otherwise instructed by your healthcare practitioner. Using essential oils with children has specific guidelines based on age. Supervise the use of essential oils in children with your healthcare practitioner.
Essential oils shouldn’t be taken internally unless under the guidance of healthcare practitioner. Most of the benefits of essential oils will be through topical or aromatherapy methods.
For Aromatherapy (inhalation):
- Add to a diffuser
- Add to a Diffuser necklace
- Inhaler stick for on the go
- Mix into salve to make a cooling chest rub
- Pressure point massage
- Mix into a salve for cooling joint massage
- Rub on temples and forehead for a cooling sensation
Safety and Side Effects of Peppermint Essential Oil
Peppermint oil contains two toxic compounds, menthofuran and pulegone, which can be toxic to the brain. 
A lethal dose in rats is at a very high dose of 4,400 mg/kg. 
Contact dermatitis has also been reported from peppermint essential oil. 
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- “All about Peppermint Essential Oils.” www.newdirectionsaromatics.com/blog/products/all-about-peppermint-oil.html.
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- Joulaeerad, Narges et al. “Effect of Aromatherapy with Peppermint Oil on the Severity of Nausea and Vomiting in Pregnancy: A Single-blind, Randomized, Placebo-controlled trial.” Journal of reproduction & infertilityvol. 19,1 (2018): 32-38. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5960050/.
- Oh, Ji Young et al. “Peppermint Oil Promotes Hair Growth without Toxic Signs.” Toxicological researchvol. 30,4 (2014): 297-304. doi:10.5487/TR.2014.30.4.297 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4289931.