j. Cosmet. Sci., 51,141-151 (March/April 2000) Fragrance perception: From the nose to the brain PAMELA DALTON, Monell Chemical Senses Center, 3500 Market Street, Philadelphia, PA 19104. Accepted for publication February 15, 2000. Presented to the New York Chapter of the Society of Cosmetic Chemists, November 4, 1998. Synopsis Fragrance is a major component in many personal products, influencing their acceptability and, in some cases, their perceived efficacy. Despite claims that certain fragrances can relax or energize, there is surpris- ingly little scientific evidence in support of direct, physiological effects of fragrances. Rather, recent research suggests that psychological factors, such as personal experience, expectations, and the surrounding context may be among the most important factors that determine how a fragrance is perceived. INTRODUCTION Among humans, the ability to perceive volatile chemicals through our sense of smell is often considered to be far less important than perception via other sensory modalities such as sight or sound. In stark contrast to this view, considerable scientific, anthropo- logic, and economic evidence exists to suggest that stimulation of olfaction through the perception of environmental volatiles, fragrance materials, or scented products is of paramount importance to humans. Odor perception provides information that guides our responses to the environments in which we live (1) and the individuals we encounter. At a commercial level, the significance of our response to olfactory stimulation is illustrated by the fact that the fragrance industry is a multibillion dollar industry that supplies products to scent shampoo, deodorants, tissues, soaps of all types, hand creams, leather products, toys, air fresheners, cleaning products, and many other commodities. In many commercial contexts, the addition of fragrance can serve a primary or secondary purpose. For example, in some applications, such as air fresheners or perfumes, the delivery of a pleasing scent (and the masking of an unpleasant one) is often the primary function of fragrance. In other products, such as shampoos, lotions or soap, both the immediate and lingering scent provides a secondary dimension that, in addition to its hedonic impact, can also serve to reinforce perception of the product's purpose and efficacy. From an anthropological perspective, the meaning and significance of odors in everyday human experience has historically been quite varied. Prior to the discovery of germ theory, for example, unpleasant odors were deemed to be carriers of disease and good 141

142 JOURNAL OF COSMETIC SCIENCE odors were viewed as potentially curative, or at least protective (2,3). For example, the habit of perfuming gloves and handkerchiefs seems to have originated as a way of protecting the wearer from the foul and "disease producing" smells permeating Europe during the Middle Ages and Renaissance. In an attempt to protect his troops from airborne disease, Napoleon commissioned a "bad smell map" of Egypt to guide their movements in the early nineteenth century (4). We should, perhaps, not find it sur- prising that many of these attitudes and beliefs still exist, being embodied in reactions to odors that range from concerns about becoming sick from exposure to environmental odors (5,6) to attempts to be healed through exposure to natural aromas (7,8). Some of the most extreme claims for the positive benefits of fragrance derive from the field of aromatherapy. The resurgence of interest in the use of essential oils and volatiles highlights the persistence of the belief that certain fragrances have beneficial effects on health, mood, and mental well-being (7-10). Although anecdotal experience informs us that exposure to fragrances that we like or fragrances that are associated with happy memories or favored individuals can elevate our mood, aromatherapy's claims go beyond such second-order associative or placebo effects of fragrance. Aromatherapists contend that positive benefits are derived from the actual properties and characteristics of these derivatives, which are active, independently therapeutic agents (11). As might be ex- pected, this assertion has provoked considerable controversy between aromatherapists and the scientific and medical establishment. Although inhalation or dermal absorption of lipophilic compounds can introduce these chemicals into the bloodstream, many scientists believe that the amounts that will be absorbed in these applications are not physiologically significant doses and, thus, that any systemic effects (positive or nega- tive) from inhaled or absorbed oils are negligible. Unfortunately, there is little in the way of scientific evidence to support or refute this idea. However, it is equally plausible that the effects of scent can exert powerful effects on mood and well-being through psychological mechanisms alone, and in this domain, there is considerable scientific research to inform us. OLFACTORY RESEARCH AND FRAGRANCE PERCEPTION: WHAT'S THE CONNECTION? Correlated with the increased interest in aromatherapy and other therapeutic uses of fragrance is a proliferation in the number of scientific studies of odor perception in humans and the impact of odors on mood, memory, and perceived well-being. Between 1990 and the present, MedLine (the National Library of Medicihe's [NLM] premier bibliographic database covering the fields of medicine, nursing, dentistry, veterinary medicine, the health care system, and the preclinical sciences) lists more than 650 published, scientific articles on the subject of human oilaction, suggesting that there have been considerable scientific advances in our understanding of both the mechanism and function of the human olfactory system and the effect of odors on mood, mental state, or performance. Among these references, however, there are no studies that provide unequivocal evidence that exposure to specific fragrance materials at concentrations that are commonly encountered in perfumes or scented products produces measurable direct effects (positive or negative) on human health or well-being. Instead, much of the evidence suggests that the first, and perhaps the foremost, impact of fragrance is through the conscious perception of odor. Because our ability to perceive odors has an indisput-