Cinnamaldehyde (cinnamic aldehyde, cinnamal) is a naturally occurring aldehyde in many plants. The clear yellow liquid is extracted mainly from cinnamon bark (cinnamomum cassia, cinnamomum zeylanicum) and has a strong spicy aroma and sweet taste. For this reason it is commonly used as a flavorant and fragrance in foods, cosmetics, and other products. It has also been commonly reported to cause  allergic contact dermatitis, as it is a known skin irritant and strong sensitizer .

Cinnamaldehyde was first isolated from Cinnamon essential oil in 1834. Cinnamon contains approximately 1 to 3.5% essential oil. The oil itself, is approximately 70 – 90% cinnamaldehyde. The oil has been used to impart such fragrances as almond, apricot, butterscotch, hyacinth, and lilac.  It has been recognized in Europe as the most common organic allergen in humans, second  only to Nickel. In fact, do to its potential for allergenicity, the European Union has listed cinnamaldehyde and cinnamic alcohol as fragrance materials that must be labeled on consumer products (essential oils often appear on labels as : “essential oil mix” or ” natural fragrance”).

Flavorant

       soft drinks                      

    chewing gum , candy                  

ice cream, baked goods

mouthwashes, dentifrices

---

Fragrance

perfumes (sweet/fruity) 

detergents, household cleaners

cosmetics, soaps

When ingested or topically applied, cinnamaldehyde is metabolized by an enzyme; known as aldehyde dehydrogenase, into cinnamic acid and cinnamic alcohol.  Cinnamic alcohol converts back into cinnamaldehyde by alcohol dehydrogenase. Both cinnamaldehyde and cinnamic alcohol are sensitizers, and can cause an immunotoxic response by binding covalently (strong chemical bond) to proteins. Cinnamic acid is an end product that does not have this propensity, and is detoxified by β-oxidation to benzoic acid and glycine; which is then excreted mainly in the urine. The biotransformation process can also deplete glutathione; an endogenous antioxidant (made by the body).

Contact Dermatitis

Contact dermatitis is caused by exposure of skin to an irritant or allergen – both of which cinnamaldehyde is known to be. Contact dermatitis is an adverse response that manifests as two distinct inflammatory processes; irritant dermatitis and allergic contact dermatitis. The two have clinically indistinguishable characteristics: erythema (redness), induration (thickening/firmness), scaling (flaking), and visitation (blistering).

Irritant Dermatitis – direct action of a chemical on the skin. Repeated exposures are necessary to produce a clinically apparent reaction. The severity of the reaction is proportional to the dose. It can eventually result in eczema and/or allergic contact dermatitis; upon repeatedly exposure.

Allergic Contact Dermatitis – a T-cell mediated delayed (type IV) hypersensitivity reaction. This is a true allergy; requiring only very small amounts of the agent to elicit an immune response. One must first have sufficient contact with a potential allergen and become sensitized to it. Subsequent exposure then causes a pathological response.

Cinnamaldehyde causes allergic contact dermatitis because it acts as a hapten; a low molecular-weight chemical that binds proteins. It penetrates the stratum corneum (top layer of skin), and links with carrier proteins in the epidermis. When it binds protein nucleophiles in the skin, it forms immunogenic complexes that the body recognizes and launches an attack.

In summary, cinnamaldehyde is approved by the U.S. Food and Drug Administration (FDA) for use in foods, and  “generally recognized as safe” by the Flavor and Extract Manufacturers’ Association in the United States. Cinnamaldehyde is a more potent sensitizer than cinnamic alcohol, but both compounds as well as other cinnamic derivatives are skin irritants. While limits have been placed on the level of the chemical permitted in consumer products and foods, the threshold for irritant dermatitis varies from person-to-person. Cinnamic Aldehyde is also readily absorbed in the gut, and can irritate mucus membranes of the gastrointestinal tract. Due to its widespread use, even though present in restricted “safe” concentrations, persons may be frequently and chronically exposed to cinnamaldehyde; both dermal and orally. Cinnamaldehyde has other uses as a medicine and has been approved by the Environmental Protection agency (EPA) as a pesticide. It acts as an insecticide against mosquito larvae, a fungicide in agriculture, and an animal repellent against cats and dogs.