Menthol, camphor and other actives: mechanism, levels and the drug line

How menthol cools through TRPM8, the real monograph levels for camphor and menthol (they are not in Part 348), the toxicity numbers, and whether menthol dries lips.

Menthol and camphor are the two ingredients that make a balm feel like it is doing something. That sensation is real, it is well understood at the receptor level, and it is also the reason both materials sit awkwardly across the line between a cosmetic and a regulated drug.

This page covers the mechanism, the levels commercial products use, which US monograph actually applies (it is not the one everybody cites), the toxicity figures worth quoting exactly, and the other actives makers keep asking about.

How cooling actually works: TRPM8

TRPM8 is an ion channel in sensory nerve endings in skin and mucosa. It opens when the tissue drops below roughly 26 C, and the resulting signal is what the brain reads as cold. Menthol binds the channel and opens it at ordinary skin temperature, so the nerve fires while the skin sits at 32 C.

Three consequences follow, and they explain most of what people notice.

• Nothing is actually cooled. No heat leaves the tissue, so a menthol product does not reduce inflammation by cooling it.
• The sensation fades fast. The channel desensitises, so a strong hit of menthol reads as intense for a few minutes, then flattens. This is why menthol products invite reapplication.
• Real cold still registers. Going outside after applying a menthol balm genuinely feels colder, because the real cold and the chemical signal add up.

Menthyl lactate and the WS-series coolants (WS-3, WS-23) act on the same channel with far less odour and irritancy, which is why they dominate confectionery and modern lip products. Their use is covered in lip balm flavour and sweeteners.

What a counter-irritant is

A counter-irritant produces a mild, controlled surface sensation that competes for attention with a deeper discomfort. Menthol, camphor, methyl salicylate and capsicum are the classic examples. The mechanism is partly gate control, partly distraction, partly a modest local increase in blood flow.

A counter-irritant changes the sensation, not the underlying tissue, and anything beyond that is a therapeutic claim. Note the word inside the term: the mechanism is irritation, deliberately produced. That is why these materials suit already irritated skin badly, and why the strong versions belong in a muscle rub balm rather than a face product.

Camphor is the more complicated of the two. It smells cool but acts largely on warmth and pain channels rather than TRPM8, so a camphor balm reads as warming and slightly numbing. It is also the more toxic material if swallowed.

Typical levels in commercial products

Levels vary hugely because the category varies. A tinted lip balm and a chest rub are separated by a factor of fifty in menthol content.

Worked example, weight percent of the total, totalling 100. A 250 g foot balm at 1% menthol needs 2.5 g of menthol crystals, dissolved into a portion of the warm liquid oil before the wax goes in. Undissolved crystals concentrate the sensation into points and sting.

The line where a balm becomes a drug

In the United States a product is a cosmetic if it is intended to cleanse or beautify, and a drug if it is intended to treat, prevent or affect the structure or function of the body. Intent is shown by claims and by formulation, so a product can become a drug in two independent ways.

The claims side of the boundary catches far more small makers than the formulation side, and it is set out in cosmetic versus drug claims; what the label must then carry is in labelling cosmetics in the US. Sun protection is a separate case again, covered in SPF in lip balm.

Which monograph applies, and the Part 348 correction

Almost every craft source quoting menthol and camphor levels attributes them to 21 CFR Part 348. That is wrong: Part 348 as codified covers only male genital desensitising drug products. The levels people mean are in OTC Monograph M017, external analgesics, and the chest rub levels are elsewhere again, in the antitussive monograph at 21 CFR 341.74(d). The three sets are not interchangeable.

Three further points rarely appear anywhere. Cold sore products are governed by 21 CFR 310.545(a)(10)(v), which makes camphor above 3%, menthol above 1%, methyl salicylate, eucalyptus oil, turpentine oil, capsaicin and eugenol non generally recognised as safe and effective for that use, so the popular homemade cold sore salve is built almost entirely from materials FDA has specifically excluded. Eucalyptus oil has no US OTC monograph status at all, in any category. And camphorated oil is a new drug requiring an approved application, which is why it left pharmacy shelves.

Skin protectants, and the beeswax surprise

The monograph that actually covers a lip balm is 21 CFR Part 347 (OTC Monograph M016). Section 347.3 defines a lip protectant drug product "traditionally called lip balm". Its permitted actives are ordinary balm materials at high percentages, which is why so many mainstream lip balms carry a Drug Facts panel.

The surprise is what is excluded. 21 CFR 310.545(a)(18)(i)(B) declares beeswax not generally recognised as safe and effective as a skin protectant active. That does not touch its use as a cosmetic ingredient, where it remains the backbone of most balms, but beeswax cannot be the claimed drug active on a Drug Facts panel. Shark liver oil is not a skin protectant either: it is an anorectal active under Part 346.

The under-2 rule, and the camphor numbers

This is not a cautious house rule. It is the reason mainstream chest rubs carry an explicit age warning, and the reason a "gentle" homemade chest balm for a toddler is one of the more genuinely risky things a hobby maker can produce. The same logic constrains the aromatic load of a chest rub balm generally.

The published figures are worth quoting exactly rather than paraphrasing. Exposure to as little as 500 mg of camphor has been cited as a cause of mortality, 750 to 1000 mg is associated with seizures and death, and in children under 6 an exposure of 500 mg or more requires rapid triage (Love et al., Journal of Emergency Medicine 2004;27(1):49, PMID 15219304). Put that in balm terms: a chest rub at 5% camphor carries 500 mg in 10 g of product, which is a blob the size of a large grape.

Methyl salicylate is worse per millilitre. The poison control consensus guideline sets the referral threshold at more than a lick or taste of oil of wintergreen by a child under 6, or more than 4 mL by anyone aged 6 or over, either of which warrants emergency department referral (PMID 17364628). Wintergreen and sweet birch oils are 85 to 99% methyl salicylate, so a teaspoon is a genuine poisoning.

One study is routinely misused in this area. Abanses and colleagues reported that a vapour rub raised mucin secretion by 63% and lowered ciliary beat frequency by 35% (PMID 19136404). That is an excised ferret trachea model plus a single case report, not a human clinical trial, and consumer media present it as though it were. It is a reason for caution in infants and a reason not to use vapour rubs under the nose, not proof of harm in adults.

"Menthol dries my lips": what is plausibly happening

This complaint deserves a real answer rather than a dismissal. Menthol does not remove water from tissue and is not hygroscopic. Four mechanisms are plausible, and more than one is usually running at once.

1. Irritant cheilitis. Lip vermilion has a thin stratum corneum, almost no sebaceous glands and a poor barrier. Repeated low-grade irritation, several times a day for weeks, produces exactly the dryness, scaling and fissuring people describe.
2. Allergic contact cheilitis. Menthol and peppermint oil are documented contact allergens. Once sensitised, a person reacts at tiny doses and the reaction looks like severe chapping, which prompts more application of the offending product. The reaction is delayed by a day or two, which hides the connection.
3. The behavioural loop. The cooling desensitises within minutes, so the product asks to be reapplied, which encourages lip pressing and licking. Evaporating saliva is genuinely drying and leaves digestive enzymes behind.
4. The base, not the active. Medicated lip products are often built on thin, quick-absorbing bases so they do not feel heavy. A base with weak occlusion does less to slow water loss, so the lips are drier regardless of what the active is doing.

The diagnostic move is to change one variable: use an unscented, unmedicated balm with a strong occlusive load for two weeks. If the lips settle, the active or the fragrance was the problem. The wider argument, including why "lip balm addiction" is not a described condition while contact cheilitis very much is, sits in does lip balm dry your lips. Immediate stinging is triaged in balm stings or burns.

The other actives makers ask about

Allantoin is a white crystalline powder, poorly soluble in oil, used at 0.2 to 0.5% cosmetically and a skin protectant active at 0.5 to 2%. Grind it into a little oil first, or it stays as visible specks.

Panthenol is the one people most often waste. It is a humectant, and in an anhydrous formulation there is no water for it to hold and no solvent for it to dissolve in, so it separates as syrupy droplets. Adding it because the ingredient list looks better is a real cost with no benefit.

Zinc oxide disperses rather than dissolves and needs wetting, ideally in castor oil, then grinding. It gives opacity and a dry, astringent finish. Weigh it without raising dust, and remember that both the skin protectant and the sunscreen routes are drug categories.

Salicylic acid and phenol are not home formulation materials. Both are drug actives with real toxicity profiles, and salicylic acid is capped at 0.5% in lip products and 2.0% elsewhere under EU Annex III, and barred for children under 3.

A reasonable position for a maker

Sensory actives are legitimate and people like them. The mistake is treating the sensation as evidence of repair. Decide what the product is for: if the answer is occlusion and comfort, the actives add nothing and the effort belongs in the wax, butter and oil balance. If it is a cooling foot or muscle product, dose the menthol properly, dissolve it fully, keep it away from children and lips, cite the right monograph, and check the current text rather than a remembered percentage. Aromatic materials carry their own separate limits, in essential oils in balms.

Reviewed and updated 6 September 2026. Spotted an error? Tell us and we will fix and log it.