Fragrance is a very important part of any cosmetic or cosmeceutical. Smell evokes important human emotions, both positive and negative, and can create a perception of beauty. Pleasant smells have a potent effect on the central nervous system creating well-being and a positive image. Indeed, cosmetics create their allure based on smell, feel, and appearance. It is no wonder that the most expensive part of any product development, excluding the packaging, is the fragrance.
While dermatologists hear fragrance and think allergic contact dermatitis, the pervasive nature of fragrances in skin care products makes an understanding of their use and composition worthwhile. This article examines the world of smell examining the composition and use of fragrances to create a positive allure.
Fragrance is a complex composition of aroma materials that can be divided into three categories: terpenols, aliphatics, and benzoids. The earliest fragrance materials were derived from oil of terpentine, accounting for the name terpenoids. Terpenoids are based on a five carbon unit, known as an isoprene. Examples of terpenoid fragrances include lemongrass, linalool (a component of lavender), menthol, and camphor. These early fragrances are still widely used in cosmetics and OTC drugs today.
Aliphatics are the largest fragrance category used in modern scents. This fragrance family includes aldehydes, alcohols, esters, ketones, and lactones. Finally, the benzoids are derived as a by-product of coal tar processing and include benzyl acetate, a component of jasmine fragrance, phenylethyl alcohol, which smells likes roses, and cinnamic aldehyde, which provides a cinnamon fragrance.
Fragrances and masking fragrances are one in the same, but have a different purpose. Fragrances are designed to create a perceivable pleasant smell while masking fragrances are designed to mask a bad smell creating a neutral smell. Some commonly used raw materials have a foul odor that must be covered to increase consumer acceptability. Examples include the odor of ammonium thioglycolate, accounting for the rotten egg smell of permanent hair waving solutions, which requires a masking fragrance to allow the consumer to sit with the solution on the hair. Another example is the quaternized nitrogen compounds, also known as quats, commonly found in hair conditioners. These require some type of masking fragrance. Even some surfactants used to cleanse the skin and hair require a masking fragrance for consumer acceptance.
The goal of a masking fragrance is to give the perception that the product is unscented. Thus, unscented does not mean fragrance free, but rather smell free. However, most products are deliberately scented to imply certain aspects of their functionality. For example, consumers believe that citrus fragranced household cleansers work better than unscented cleansers. Dandruff shampoos that have a menthol medicinal smell are thought to alleviate itch better than unscented shampoos. Fragrance can also be used to imply the presence of an ingredient, such as a product containing strawberry extract can be fragranced like strawberries. The fact remains that consumers believe products work better with certain scents! The places tremendous importance on the very primitive olfactory center of the brain.
Fragrances are made from volatile molecules with low molecular weight and low vapor pressure. The characteristics of a fragrance are discussed in terms of notes, borrowing a term from music. A fragrance can be described in terms of top, middle, and bottom notes, with a good fragrance containing all three notes. Top notes are the most volatile of the fragrance ingredients accounting for the smell as soon as the product is opened. These evaporate rapidly leaving behind the middle notes, which form the body of the fragrance. Finally, the bottom notes are perceived, which are the least volatile and longest lasting. Citrus scents are common top notes, floral scents are common middle notes, and vanilla is a common bottom note.
Many of the newer fragrances are able to precisely match the smell of a certain flower. This is accomplished through a technique known as “head space analysis.” Head space analysis involved analyzing the gases above a living flower or other scented material to collect the constituents creating the smell. The gases are then analyzed for individual ingredients that can then be used to synthetically create more true natural scents of flowers and other biologic materials.
Fragrance ingredients can be obtained from anything that smells, but most perfumers use several traditional sources to include natural raw materials, modified natural raw materials, and synthetic raw materials. The natural raw materials can be processed to obtainin essential oils, concretes and absolutes, and resinoids. Natural raw materials for processing can be obtained from any part of the plant to include flowers, roots, berries, leaves, and seeds.
Essential oils are named based on the extraction technique used to obtain the oil. Distillation is used to obtain essential oils. Water distillation is the simplest technique where the plant is submerged in water and boiled. The steam is collected to yield the oil. For essential oils that are temperature sensitive, squeezing or scraping the plant material can express the plant material. Essential oils are created by plant metabolism to encourage pollination and are composed of terpenoids, aromatics, and heterocyclic compounds. Examples of essential oils include lemongrass, sandalwood, geranium oil, citrus, and clove oil.
Concretes and absolutes are obtained by volatile solvent extraction. In this technique, the plant material is submerged in hexane for several hours and the flower oils removed that cannot be obtained through water distillation. The result is essential oils combined with waxes and glycerides, known as a concrete. If the waxes and glycerides are removed, the result is an absolute. Examples of concretes and absolutes include rose oil, ylangylang oil, orange blossom (neroli), lavender, jasmine, and oakmoss.
Resinoids are the third category of natural fragrances derived from plants that produce resins. Resinoids are not very volatile and are used to increase the longevity of the fragrance when mixed with other essential oils. Gums, such as myrrh, and balsams, such as balsum tolu and copaiba balsam, are two important types of resinoids. Gums are obtained by boiling the bark, twigs, or leaves of a plant. Balsams are similar to gums except they contain cinnamic and/or benzoic acids yielding a spicy scent.
Synthetic raw fragrance materials are becoming more and more important as some natural fragrance ingredients are becoming scarce. With the current sustainability movement in skin care products, there is concern that certain plant materials may be over harvested and depleted. While synthetic fragrance materials are cheaper and more consistent, they are composed of one single molecule and are never a perfect match to their natural counterpart. Synthetic fragrances are derived from crude or terpentine oil. The most commonly used synthetic fragrances are benzyl acetate, vanillin, citronellol, and hexyl cinnamic aldehyde.
Some of the newer fragrances are longer lasting requiring special release techniques to insure longevity. Fragrances can be released by a variety of triggers including temperature, oxidation, light, enzymes, and pH. Sometimes even sweat and its components, such as urea and lactic acid, can release the fragrance.
Encapsulated fragrance systems can produce the longest lasting smells. The fragrance is placed in a hydrophobic sphere 100-400nm in diameter until released by a trigger as mentioned previously. One example trigger is moisture. So, for example, moisture from the lips can be used to trigger release of a fragrance, a sensory agent like menthol, or a flavor like peppermint. Since flavors are high concentration fragrances, this same technology is used to increase the longevity of chewing gum flavors.
The oldest perfume factory was unearthed in Cypress and said to date back to 2000BC. In this factory, perfumes ingredients were discovered, such as rosemary, lavendar, bergamot, and coriander. Amazingly, these ingredients are still found in modern fragrances. Man has a fundamental need to augment his experiences with smell. Smell seems to evoke moods and memories. Many humans relate their earliest childhood memories to a characteristic smell. Thus, fragrance is an important part of human perception that cannot be ignored by the dermatologist.