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Plant extracts

Peppermint oil and menthol

Also listed as peppermint oil, mentha piperita oil, menthol, mint

Mint gives toothpaste its taste and shampoos their tingle via cooling receptors. It freshens; hair-growth claims rest on one mouse study.

Weak evidenceTypical strength: Well under 1-2% in toothpaste and shampoo; 1.25-16% menthol only in pain-relief rubs

What it is

Peppermint oil is steam-distilled from the peppermint plant; menthol is its main cooling component. Both trigger the skin's cold receptors (TRPM8), producing the fresh, tingling feeling in toothpaste, mouthwash and 'invigorating' shampoos. The tingle is a sensation, not a sign that anything is being cleaned or stimulated.

At higher strengths menthol is a regulated counter-irritant in pain-relief rubs; in oral and hair care it is used at low levels.

How strong is the evidence?

Weak evidence

Mint's role in oral care is flavour and a feeling of freshness, which is not the same as reducing bad-breath bacteria. The widely shared claim that peppermint oil grows hair comes from a single 2014 study in mice; there are no controlled human trials.

What it's used for, checked

Freshens breath

Mixed

Masks odour briefly; it does not treat the cause of bad breath.

Grows hair

Unproven

One mouse study; no human trials.

Cooling, soothing scalp or skin feel

Holds up

A real sensory effect via cold receptors.

Who should be careful

  • Never apply peppermint oil or menthol products to the face or chest of babies and young children: they have triggered breathing problems.
  • Mint flavouring can cause contact allergy (sore lips, mouth ulcers or rash) in a few people; a mint-free paste settles it.
  • Undiluted essential oil irritates the scalp and eyes; use it only as formulated.

The studies

Every citation is checked against its PubMed record.

  1. Peppermint Oil Promotes Hair Growth without Toxic Signs.
    Oh JY, Park MA, Kim YC · Toxicol Res · 2014 · Animal study (mice)

    In shaved mice, 3% peppermint oil applied for 4 weeks produced more hair growth, deeper and more numerous follicles than saline, jojoba oil or 3% minoxidil. No human data.