Route Of Exposure

Allergen Exposure

The Mint family consists of fragrant aromatic plants of which the culinary and medicinal uses go back many centuries. More than 30 varieties can be obtained with different "flavours": apple, pineapple, lemon, and others. But the 3 chief species of Mint in cultivation and general use are the following: Spearmint (Mentha viridis), Peppermint or Mint (M. piperita), and Pennyroyal (M. pulegium).

Mint is a small, herbaceous perennial (0.3 m by 1 m), with a strong, fresh scent. It has lance-shaped, serrate leaves growing in opposite pairs along the stem, and flowers with unusual projecting stamens.

Mint grows wild in moist conditions, especially along banks and shores, waste seepage areas and wet meadows.

The aromatic leaves, with their strong yet pleasant taste and odour, were widely used for centuries. Tea was made from either fresh or dried leaves and hot water. This tea was also taken as a medicine for pain, colds, fevers, swellings, and colic. The leaves may be eaten raw or cooked and are used as a flavouring in salads and cooked foods.

Peppermint oil is derived from Mint and has many uses, chiefly as a flavourant but also in complementary and alternative medications for allergy. Menthol (also known as Mint camphor or Peppermint camphor) is a white, crystalline, aromatic substance, extracted from Peppermint oil or other Mint oils or made synthetically by hydronisation of thymol. Menthol is one of the most important flavouring chemicals. It is used extensively in pharmaceuticals, cosmetics and toiletries – especially toothpastes – chewing gum, candies, and alcoholic drinks. It is an important ingredient in sore throat remedies, and in creams for sore muscles, inhalers, and cooling gels. It is also found as an additive in some cigarettes, both for flavour and to reduce the throat and sinus irritation caused by smoking.

Clinical Relevance

Allergen description

No allergens from this plant have yet been fully characterised.

Potential Cross Reactivity

An extensive cross-reactivity among the different individual species of the family, particularly within the genus Mentha, could be expected and has been suggested by clinical studies. In a report describing 3 systemic allergic reactions caused by Oregano and Thyme in the same patient, skin-specific IgE tests with plants of the Lamiaceae family (Hyssop, Basil, Marjoram, Mint, Sage, Lavender, etc.) were all positive; tests were negative with Basil and lavender and positive with all the others when the prick by prick technique was used. Serum-specific IgE was detected to all herbs tested. The study concluded that “plants belonging to the Labiatae [Lamiaceae] family seem to show cross-sensitivity on the basis of clinical history and in vitro and in vivo test results.

Three naturally occurring substances in Peppermint have been reported to have sensitising properties: alpha-pinene, limonene, and phellandrene; these occur in colophony, balsam of Peru, turpentine peroxides, turpentine oil, and Peppermint oil.

clinical Experience

IgE-mediated reactions and contact dermatitis

Mint may uncommonly induce symptoms of food allergy or cutaneous allergy in sensitised individuals but it is possible that the allergy occurs more frequently than reported. Adverse events to menthol and Peppermint oil, both compounds extracted from Mint, have been more frequently reported, in particular in skin sensitisation.

Allergic contact dermatitis from Mint was first described in 1940. Occupational allergic contact dermatitis was described in 2 Florida bartenders who made drinks containing the leaves of Peppermint. Both were able to tolerate Spearmint (M. spicata).

The vast majority of recorded reactions, however, involve not Mint itself but Mint derivatives used as flavourants, particularly menthol and oil of Peppermint. Candies, toothpastes and cigarettes are major sources of these allergens. Toothpastes may the most important sources, though establishing this would be complicated by the inclusion of other allergenic flavourants (e.g., cinnamic aldehyde and cinnamon oil), as well as preservatives.

Oil of Peppermint and Spearmint, carvone and anethole, all of which come from Mints, are ingredients with a low sensitising potential, but they are used in almost every brand of toothpaste. Stomatitis, cheilitis, glossitis, gingivitis, perioral dermatitis and immediate hypersensitivity from toothpaste containing Mint substances as flavourants have been reported. Similarly, 7 cases of contact allergy in a 6-year period were reported from a hospital clinic. In yet another study, toothpaste flavours have been reported as a cause of allergic contact dermatitis.

Cheilitis was observed in a 74-year-old patient after use of a new toothpaste. The reaction occurred after several weeks despite withdrawal of the paste. Patch testing indicated sensitisation to terpene ketone L-carvone, a substance occurring naturally in many Mint and Peppermint oils. In this instance, it resulted in recurrences of symptoms when the patient sucked refreshment lozenges containing L-carvone. L-Carvone is also contained in most chewing gums, and the authors suggest that this allergen should therefore be considered as an aetiological agent in cases of cheilitis and stomatitis.

A 26-year-old woman presented with a 12-month history of persistent dermatitis of the lips. Patch testing was negative. Identification of the offending allergen occurred only following an acute flare-up immediately after dental treatment with a Mint-flavoured tooth cleaning powder. Skin-specific IgE was detected using Mint leaves.

Cheilitis has also been reported following excessive intake of Mint-flavoured sweets. Urticaria and asthma exacerbation were reported after the ingestion of menthol-containing lozenges. Contact urticaria from menthol has been reported from mentholated cigarettes, cough drops, aerosol room spray and topical medicaments. Generalised urticaria was also seen following oral challenge. A perioral eczema was due to menthol in cigarettes. Non-thrombocytopaenic purpura has also been attributed to menthol-containing cigarettes. Despite its high concentration in Peppermint oil (up to 75%), menthol was said not to be the main sensitiser.

Peppermint oil from fragrances can cause allergic contact dermatitis.

Contact dermatitis has been reported from Peppermint and menthol in a local action transcutaneous patch.

Other studies have focused more on flavouring agents in themselves than specific products. Allergic contact dermatitis has been reported as a result of menthol in 2 individuals: cheilitis of 2 years duration in a 64-year-old woman, and an 18-month history of eczema affecting the upper lip of a 62-year-old man. Patch tests for Peppermint and menthol were positive. Allergic contact dermatitis from menthol has been reported to result in stomatitis.

A report was published of12 cases of contact sensitivity to the flavouring agents menthol and Peppermint oil in patients presenting with burning mouth syndrome, recurrent oral ulceration or a lichenoid reaction. Five patients with burning mouth syndrome demonstrated contact sensitivity to menthol and/or Peppermint, with 1 patient sensitive to both agents, 3 positive to menthol only and 1 to Peppermint only. Four cases with recurrent intra-oral ulceration were sensitive to both menthol and Peppermint. Three patients with an oral lichenoid reaction were positive to menthol on patch testing, with 2 also sensitive to Peppermint. Nine of the 12 cases demonstrated additional positive patch test results.

Menthol-induced asthma was described in a 40-year-old woman with no history of asthma or any other allergy who developed dyspnoea, wheezing and nasal symptoms when exposed to mentholated products such as toothpaste and candies. Menthol- and aspirin-induced asthma has been reported in another study.

Occupational allergy may occur. (See also above.) A former laboratory technician referred to a clinic, because of swelling of his tongue, lips, and gingival mucosa following a dental operation, was found to be sensitised to colophony, balsam of Peru, turpentine peroxides and Peppermint oil (an ingredient of several dental preparations). This was established by patch testing. Allergic contact dermatitis has also occurred in food handlers. Making Mint sauce can result in skin reactions.

Other reactions

In a study of allergic and pseudo-allergic reactions in penicillin factory workers exposed to the dust of preparations of penicillin derivatives, histamine release caused by cocoa and Peppermint were demonstrated and reported to depend on non-immunological mechanisms, i.e., pseudo-allergic reactions.

A report stated that "refractory" gastrointestinal disorders may be as a result of frequent and large use of products containing Peppermint, and in the case of "dietetic" Mint, include sorbitol. Adverse conditions include stomatitis, severe esophagitis, esophageal ulcer, hiatal hernai, gastritis, unexplained diarrhoea, and recurrent pancreatitis. Some of these symptoms may be as a result of Peppermint decreasing lower esophageal sphincter pressure thereby facilitating eophageal reflux.