For devising the odours of today's cosmetics and toiletries, the modern perfumer has available a set of some 4000 aromatic plant and animal substances and another 2000 synthetic organic compounds. The blended fragrance itself reaches the nose in three phases.

       The first impact, the top note, comes from components that vaporize easily and move to our nose quickly. A typical example is phenylacetaldehyde, which brings the odor of hyacinths and lilacs. The top note is the fragrance of the perfume that makes the first impression.

       The most noticeable odor, the middle note, is produced by compounds such as 2-phenylethanol (also known as B-phenylethyl alcohol) with its aroma of roses.

       The end note is a residual, longer lasting scent carried by substances like civetone, a cyclic organic compound with a musk like odor. The end note of a perfume is the fragrance that lingers.

       Civetone is the odorous component of the secretions of the Ethiopian civet cat and was originally obtained by prodding and scrapping the glands of the caged animals. Today a more humane preparation comes from syntheses carried out in chemical laboratories.

       Examples of the organic compounds used in blending fragrances are shown here. The choice of specific ingredients depends on the nature of the application, the chemical behavior of the available materials, and safety considerations. A nicely scented substance that oxidizes easily to a foul-smelling product could hardly be used in a face powder, which is exposed to the air for long periods. In addition to these technical factors, though, consumers' perceptions and expectations come into play as well. A deodorant soap, for example, might carry a strong smell suggesting the clean air of a forest, yet the scent of a lipstick must be more subtle and too weak to interfere with the taste of food and drink.

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