To Smell or Not to Smell? That is the Question!

Abstract

Fragrance is an important part of cosmetic dermatology creating perceptions of beauty, 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. Although dermatologists hear fragrance and think allergic contact dermatitis, the pervasive nature of fragrances in skin care products and their consumer-perceived importance demand an understanding of the complexity of smell. Fragrances are highly aromatic materials derived from three chemical groups: 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 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 the longest lasting ones. Citrus scents are common top notes, floral scents are common middle notes, and vanilla is a common bottom note. 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 obtain 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. 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. Although 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. 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 involves 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. This has accounted for the plethora of new fragrances in everything from laundry soap to candles to room fresheners to cosmetics. One of the newest developments in fragrance is the ability to make the scent longer lasting. This is accomplished through the use of triggering agents that can provide sustained release over time. 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. The oldest perfume factory was unearthed in Cypress and said to date back to 2000BC. In this factory, perfume ingredients were discovered, such as rosemary, lavender, bergamot, and coriander. Amazingly, these ingredients are still found in modern fragrances. Why does fragrance continue to be important in cosmetic dermatology in 2013 after nearly 4000 years? Fragrance remains important because it speaks to a very important human sense. The olfactory bulb is located in one of the oldest areas of the brain. In the world of cosmetics, the importance of speaking to this human need is addressed in great detail. The science of beauty and scent are forever mingled. Humans cannot turn off this important neural input and cosmetic dermatology recognizes that a pleasant smell is part of the aura of beauty.