Menthol

C 10
H 20
O 1

Ball-and-stick Stick Space-filling

Drag to rotate; pinch or Ctrl + scroll to zoom. Arrow keys rotate, + − zoom, R resets.

31 atoms, 31 single bonds.

IUPAC name: (1R,2S,5R)-5-methyl-2-propan-2-ylcyclohexan-1-ol
Molar mass: 156.269(25) g/mol
Atoms: 31
SMILES: CC1CCC(C(C1)O)C(C)C
InChIKey: NOOLISFMXDJSKH-KXUCPTDWSA-N
PubChem CID: 16666

Made of

C H O

Structural formula of menthol. Each unlabelled corner is a carbon atom, and the 10 hydrogens on carbon are not drawn. Wedges come toward you, hashes go back. It shows which atoms are joined to which, not the shape. The model above shows the shape.

Peppermint oil and the other mint oils contain menthol, according to Haz-Map, a US database of workplace hazards. The Flavor and Extract Manufacturers Association (FEMA) sums up its flavour in two words, mint and cool. Pure menthol forms colourless hexagonal crystals, usually needle-like, with a pleasant peppermint smell, as the Joint Expert Committee on Food Additives of FAO and WHO (JECFA) describes it.

Each molecule holds ten carbon atoms, twenty of hydrogen and one of oxygen, C₁₀H₂₀O, for a molar mass of 156.27 g/mol. The IUPAC name reads it as a cyclohexan-1-ol, a six-carbon ring with the OH on carbon 1, a propan-2-yl (isopropyl) group on carbon 2 and a methyl on carbon 5. The labels 1R, 2S and 5R fix those three groups in space. ChEBI, the Chemical Entities of Biological Interest database, classes it as an alcohol, p-menthan-3-ol. It dissolves readily in alcohol and volatile oils but only slightly in water, JECFA reports.

Structure and bonding

The viewer draws 31 atoms joined by 31 bonds, every one of them single. With Labels switched on, each atom carries its symbol, C, H or O. One ring carbon holds the hydroxyl group, an oxygen bonded to a hydrogen. Its neighbour carries an isopropyl group, a carbon bearing two methyls, and the carbon two places from the hydroxyl on the other side carries a lone methyl.

In Ball-and-stick, each ring carbon has four neighbours around it at the corners of a tetrahedron, the coordination Chem1 describes for carbon with four single bonds. The ring’s C–C–C angles in PubChem’s computed model run from 110.6° to 111.9°, and the C–O–H angle is 108.0°. Stick thins the atoms away, leaving the three branches as bare lines. Space-filling swells every atom to full size: white hydrogens coat nearly the whole outline, and the single red oxygen shows at one spot on it.

With no double bond and no ring of alternating bonds, the drawing is the real bonding and no resonance form stands in for it. Three ring carbons are stereocentres, carbons whose groups can take two mirror-image arrangements. The model shows (−)-menthol, which ChEBI records as the mirror image of (+)-menthol.

Where it turns up

Outside mint, the LOTUS natural-products database reports p-menthan-3-ol in the tea plant, Camellia sinensis, and in the potato, Solanum tuberosum. Haz-Map lists menthol as a flavour or fragrance in liqueurs, sweets, perfumes, cigarettes, cough drops and nasal inhalers. According to the Hazardous Substances Data Bank (HSDB), it also goes into chewing gum, chest rubs, throat lozenges, shaving creams, toothpastes, mouthwashes and shampoos. California’s Safe Cosmetics Program counts 1,285 cosmetic products reporting one of its forms.

Some uses have nothing to do with the body. Haz-Map records menthol controlling mites in Canada and going into paints, lacquers, adhesives, metal-care and cleaning products in Europe. In 1981, according to HSDB, cigarettes and tobacco took 60 per cent of menthol consumption, salves and lotions 15 per cent and oral products 12 per cent. The EPA’s Chemical Data Reporting puts the 2023 US volume of (−)-menthol at 10 to under 25 million pounds.

Why it matters

Menthol earns its place in medicine on the skin and in the throat. ChEBI lists it as an antitussive, which quiets a cough, an antispasmodic, which eases muscle spasm, and an antipruritic, which relieves itching. NCI Thesaurus, the US National Cancer Institute’s vocabulary, describes a counterirritant action on the skin and on mucous membranes that produces local pain relief or numbness. A counterirritant causes a mild irritation of its own where it is applied. HSDB records it in nose and throat preparations and in ointments that relieve local irritation, and the WHO’s veterinary drug index files levomenthol among anaesthetics.

In foods and medicines, NCI Thesaurus notes, menthol strengthens peppermint flavours, and JECFA classes it among flavouring agents. Inside the body, according to HSDB, L-menthol is glucuronidated, joined to glucuronic acid, rapidly but incompletely. Rabbits do the same readily, forming L-menthyl-β-D-glucuronide, while dogs oxidise much of it instead. Among its known human metabolites is p-menthane-3,8-diol, on the NORMAN Suspect List Exchange. One bacterium, Corynebacterium strain RWM1, grows with (−)-menthol as its only carbon source.

Properties

Properties of menthol Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 16666.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₁₀H₂₀O
Molar mass	156.269(25) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	10
Hydrogen atoms	20
Oxygen atoms	1
Bonds	31
PubChem molecular weight	156.26 g/mol	g/mol	PubChem

Safety

Pure menthol irritates the skin and eyes. Under the Globally Harmonized System (GHS), European Chemicals Agency notifications give it the signal word Warning, with skin irritation in 97.6% of them and serious eye irritation in 31.9%. It also irritates the mucous membranes and upper airways, according to CAMEO Chemicals, and Haz-Map lists it among established contact allergens in humans. The PubChem Laboratory Chemical Safety Summary for menthol holds the full hazard data.

Questions

What does a menthol molecule look like in 3D?

It is a ring of six carbon atoms carrying three groups: a hydroxyl (OH) on one carbon, an isopropyl on the next, and a methyl two places from the hydroxyl on the other side. The formula C₁₀H₂₀O gives 31 atoms joined by 31 single bonds, with no double bond anywhere. Three of the ring carbons are stereocentres, carbons whose attached groups can point in two mirror-image ways, and the model shows the (1R,2S,5R) arrangement that ChEBI calls (−)-menthol.

Where does menthol come from?

Menthol comes from peppermint and other mint oils, or it is made by hydrogenating thymol, according to HSDB. The synthetic product is levo-menthol, the mirror form that turns polarised light to the left, at 99.9 per cent purity. HSDB lists technical, USP (United States Pharmacopeia) and FCC (Food Chemicals Codex) grades, and the pharmacopoeia treats L-menthol and DL-menthol, the mixture of both mirror forms, alike.

What is the difference between (−)-menthol and (+)-menthol?

The two are mirror images with the same atoms and bonds, differing only in how the groups at three ring carbons point in space. ChEBI records (−)-menthol, the form in the viewer, as the one most common in nature. Dissolved in alcohol it rotates polarised light to the left, with a specific rotation of −50° on HSDB's figure. A mixture of both forms, DL-menthol, is a white crystalline solid.

Is menthol safe to put on your skin?

Menthol goes into chest rubs, ointments, shaving creams and shampoos, yet the pure substance is a skin irritant carrying the GHS signal word Warning. Haz-Map lists it among established contact allergens in humans, and California's cosmetics programme names it a fragrance allergen, a hazard only to people who have fragrance allergies. The PubChem Laboratory Chemical Safety Summary for menthol sets out the full hazard data.

Made of the same elements

C₁₃H₁₈O₂ Ibuprofen 33 atoms, 33 bonds.
C₁₅H₁₆O₂ Bisphenol A 33 atoms, 34 bonds.
C₁₄H₁₄O₃ Naproxen 31 atoms, 32 bonds.
C₁₈H₂₄O₂ Estradiol 44 atoms, 47 bonds.
C₁₂H₂₂O₁₁ Lactose 45 atoms, 46 single bonds.
C₁₂H₂₂O₁₁ Sucrose 45 atoms, 46 single bonds.
C₄H₉OH 1-Butanol 15 atoms, 14 single bonds.
C₉H₈O₄ Aspirin 21 atoms, 21 bonds.

All 51 compounds made of carbon, hydrogen and oxygen

C₂H₅OC₂H₅ Diethyl ether 15 atoms, 14 single bonds.
C₈H₈O₃ Methyl salicylate 19 atoms, 19 bonds.
C₈H₈O₃ Vanillin 19 atoms, 19 bonds.
C₆H₅CHO Benzaldehyde 14 atoms, 14 bonds.
C₆H₁₂O₆ Fructose 24 atoms, 24 single bonds.
C₆H₁₂O₆ Glucose 24 atoms, 24 single bonds.
C₆H₅COOH Benzoic acid 15 atoms, 15 bonds.
C₄H₈O Butanone 13 atoms, 12 bonds.
C₆H₅OH Phenol 13 atoms, 13 bonds.
C₁₉H₂₈O₂ Testosterone 49 atoms, 52 bonds.
C₃H₇OH 1-Propanol 12 atoms, 11 single bonds.
C₃H₇COOH Butyric acid 14 atoms, 13 bonds.
CH₃COOC₂H₅ Ethyl acetate 14 atoms, 13 bonds.
C₃H₈O Isopropyl alcohol 12 atoms, 11 single bonds.
C₁₆H₃₂O₂ Palmitic acid 50 atoms, 49 bonds.
C₂₀H₁₄O₄ Phenolphthalein 38 atoms, 41 bonds.
C₇H₆O₃ Salicylic acid 16 atoms, 16 bonds.
C₃H₈O₂ Propylene glycol 13 atoms, 12 single bonds.
C₃H₆O Acetone 10 atoms, 9 bonds.
C₆H₈O₆ Ascorbic acid 20 atoms, 20 bonds.
C₃H₈O₃ Glycerol 14 atoms, 13 single bonds.
C₆H₈O₇ Citric acid 21 atoms, 20 bonds.
CH₃OCH₃ Dimethyl ether 9 atoms, 8 single bonds.
C₂H₅OH Ethanol 9 atoms, 8 single bonds.
C₂₁H₃₀O₂ Progesterone 53 atoms, 56 bonds.
C₂H₅COOH Propionic acid 11 atoms, 10 bonds.
C₂H₆O₂ Ethylene glycol 10 atoms, 9 single bonds.
C₃H₆O₃ Lactic acid 12 atoms, 11 bonds.
C₁₈H₃₄O₂ Oleic acid 54 atoms, 53 bonds.
CH₃CHO Acetaldehyde 7 atoms, 6 bonds.
C₂H₄O Ethylene oxide 7 atoms, 7 single bonds.
C₄H₆O₅ Malic acid 15 atoms, 14 bonds.
CH₃COOH Acetic acid 8 atoms, 7 bonds.
C₂₁H₃₀O₅ Cortisol 56 atoms, 59 bonds.
CH₃OH Methanol 6 atoms, 5 single bonds.
C₄H₆O₆ Tartaric acid 16 atoms, 15 bonds.
C₂H₄O₃ Glycolic acid 9 atoms, 8 bonds.
CH₂O Formaldehyde 4 atoms, 3 bonds.
HCOOH Formic acid 5 atoms, 4 bonds.
H₂CO₃ Carbonic acid 6 atoms, 5 bonds.
H₂C₂O₄ Oxalic acid 8 atoms, 7 bonds.
C₂₇H₄₄O Cholecalciferol 72 atoms, 74 bonds.
C₂₇H₄₆O Cholesterol 74 atoms, 77 bonds.