Peppermint Mentha piperita is a herbaceous plant of the Lamiaceae family. It is the result of a hybridization between spearmint and water mint. It is found all over the world but it is mainly produced in Europe, North America, temperate regions of Asia, India and countries around the Mediterranean Sea. It is widely used in cooking and in industry to produce flavorings.
Its medicinal and aromatic virtues have been known for centuries. It was already used by the Greeks and Romans. Traces of it have even been found in the Egyptian pyramids. From the 17th and 18th centuries, it was used to treat colds and respiratory ailments.
Peppermint essential oil is still used for these purposes today as well as to stimulate the body and mind, relieve nausea and other digestive disorders and headaches. It also fights effectively against itching and skin irritation. It is very rich in menthol, a monoterpene largely responsible for its therapeutic virtues.
A 2018 double-blind, placebo-controlled study investigated the effect of peppermint essential oil on mood and cognition. 24 healthy adults consumed a placebo or encapsulated peppermint essential oil, before taking various cognitive tests and having their mood assessed. The group who took peppermint showed better cognitive test scores and less mental fatigue. Another animal study has shown that it increases walking behavior and memory (KENNEDY & al., 2018).
A 2008 study of 144 volunteers also found it to increase alertness (MOSS & al., 2008).
Many studies have proven the anti-bacterial effect of peppermint essential oil on several bacteria including: Staphylococcus aureus, Klebsiella spp., Microccoccus flavus, Staphylococcus epidermidis, Salmonella enteritides, Salmonella typhimurium, Escherichia Coli, Pseudomonas aeruginosa, Bacillus subtilis, Bacillus cereus (MAHENDRAN & al., 2019 ; LUMINITA BADEA & al., 2019 ; MARWA & al., 2017).
In an in vitro study with multi-resistant Staphylococcus aureus and Pseudomonas aeruginosa, peppermint was shown to be more effective in vapor than liquid form (ACS & al., 2016).
In 2017, MOHAMED & al. tested in vitro the effect of different essential oils on the biofilms produced by Klebsiella pneumoniae. Peppermint essential oil has shown a percentage biofilm inhibition of between 69% and 98%. This effect is mainly exerted by menthol (DINIZ DO NASCIMENTO & al., 2020 ; MOHAMED & al., 2017). Peppermint also inhibits the formation of biofilms produced by Pseudomonas aeruginosa and Candida albicans in vitro (SANDASI et al., 2010).
The anti-bacterial effect of this essential oil is in part due to the fact that some of its components, in particular D-menthol, disrupt the membrane permeability of bacteria thanks to their lipophilic nature, allowing them to penetrate the cell. The hydroxyl group of menthol alters the oxidative phosphorylation of the cell (DINIZ DO NASCIMENTO & al., 2020 ; MARWA & al., 2017 ; SAHARKHIZ & al., 2012).
INOUYE & al. in 2000 proved the anti-bacterial effect of peppermint essential oil against various respiratory pathogens including Haemophilus influenzae, Streptococcus pneumoniae and Streptococcus pyogenes (INOUYE & al. , 2000).
Spraying peppermint essential oil in industrial poultry houses reduces air contamination by Enterobacteriaceae and staphylococci (WITKOWSKA & al., 2013).
Peppermint essential oil has virucidal activity in vitro against acyclovir resistant herpes viruses HSV-1, HSV-2 and HSV-1. At a non-cytotoxic concentration, it reduces the virus concentration by 82% for HSV-1 and 92% for HSV-2. A higher concentration causes the viral titration of the two herpes viruses to drop by more than 90%. This percentage can reach 99% after 3 hours of incubation. It acts on the free virus, before its penetration into the host cells by interacting with its envelope (MAHENDRAN & al., 2019 ; LUMINITA BADEA & al., 2019 ; EDRIS & al., 2007 ; SCHUMACHER & al., 2003).
In animal models, the menthol in peppermint essential oil decreases blood levels of IL-4 and IL-10 (DINIZ DO NASCIMENTO & al., 2020).
Mentha piperita essential oil inhibits between 70 and 93% of free radicals in the DPPH test (DINIZ DO NASCIMENTO & al., 2020 ; EDRIS & al., 2007).
It inhibits the growth of certain fungi, including Aspergillus fumigatus, Aspergillus niger, Fusarium moniliforme, Candida albicans (MAHENDRA & al., 2019 ; UMINITA BADEA & al., 2019 ; MARWA & al., 2017 ; SAHARKHIZ & al., 2012).
