Unpleasant fragrances

In addition, vanillin was among the three or four aroma chemicals that helped perfumers of the past to imagine a new generation of fragrance combinations. The work done in organic chemistry by chemical companies has helped perfumers who had been restrained in their creation by the avadabihty of raw materials, which include natural oils and extracts made by the enfleurage process, ie, the property of perfumes to stick on fat and greases. Those extracts were weak, flat, and unpleasant. 

Uses. Most essential oils are used directly as starting materials in the production of flavor and fragrance compositions. However, some essential oils are fractionated or concentrated by distillation, partitioning, or adsorption. Substances that are important for the desired characteristic odor and taste are thus concentrated, and other components, which possess either an unpleasant or very faint odor or are unsuitable for the application in question, are removed. 

Coumarin is a natural product occurring in the essential oils of a large number of plants, such as cinnamon, cassia, lavender and woodruff. It is used for its fragrance in many personal care products (perfumes, deodorants, soaps) and in tobacco, in household and industrial products to mask unpleasant odours and, in some countries, as a flavouring agent in food and beverages. It has also been used to treat several medical conditions. Exposure to coumarin may occur from its production, its natural presence in many plants and essential oils, and its several industrial, medical and consumer uses. 

Fig. 5.1. A sample of floral scent compounds. (1) Substituted methyl esters of benzoic acid. The ester smells unpleasantly sweet when R = H (methyl benzoate), of wintergreen when R = OH (methyl salicylate), and of concord grape when R = NH2 (methyl anthranylate). Odorants with unusual origins and biological functions include the homoterpene 4,8-dimethyl-1,3,7-nonatriene (2) and the wet-earth compound geosmin (3). Some ubiquitous fragrance compounds are ben-zaldehyde (4), benzyl alcohol (5), indole (6), (S)-linalool (7), ( )-/ -ocimene (8), and of-farnesene (9).

In a well-constructed fine fragrance the heart of the perfume needs to be contained within the lower part of the composition, since this part will remain on the skin for many hours after application. Many of these long-lasting materials, as pointed out by Carles, are rather unpleasant when smelled initially and it is part of the function of the modifiers and finally the top notes to subdue and round off the character of these products in the final accord. 

Although unpleasant, skin irritation, which manifests itself as redness (erythema) and/or swelling (oedema) is not a major problem, as once the source of irritation is removed the effect diminishes. Most fragrance ingredients are classed as mild or moderate irritants when in an undiluted form only, so the low levels found in consumer products are unlikely to be a serious source of irritation. 

On the other hand, terms such as unscented or fragrance free have no legal definitions. A product labeled with these terms still contains fragrance chemicals, even if the scent cannot be easily detected, because if a fragrance is added to a product to mask or cover up the unpleasant odor of some ingredients, it need not be mentioned on the label. 

Microcapsules with deodorization properties can be used on clothing, socks, curtains, and automotive textiles to eliminate smoke and other malodors, thereby creating pleasant surroundings. Textile coatings can also be infused with fragrances, which may intake unpleasant odors, while imparting pleasant ones, with potential applications for marketing. 

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