There are several categories of fragrances: perfume is at the top, followed by eau de parfum, eau de toilette, and eau de cologne, each containing a lesser degree of aromatic oils, respectively. The lower the concentration of aromatic compounds, the shorter the scent life. Perfume is highly prized precisely because it lasts from morning until night, and it wears well, meaning the scent stays fresh as the day wears on. In fact, a good one is designed to smell nice throughout its various stages of wear.
Aromatic compounds used in fragrances have complex chemical interactions. While consumers might imagine a group of corporate executives sniffing bottles of various mixtures to see what smells best, the truth is far more complicated. Fragrant compounds tend to breakdown quickly when exposed to heat, light and air, so in order for a scent to last throughout the day, tens or even hundreds of ingredients are used so that the product continues to "bloom." Essentially, as one group of compounds is spent, another re-enlivens the scent and adds its own tone. Perfume is said to have three notes that work together to form the lasting fragrance.
The top note is the initial scent when applied. This scent lasts only a few minutes to an hour, and may be somewhat strong. As it diminishes, it reveals the middle note of the fragrance, also called the heart or body of the scent. The aromatic compounds that make up the heart last longer, but eventually give way to the base note, or underlying tone. The optimal scent of the base note takes time to develop, so initially, it isn’t as pleasant but is masked by the top and middle notes. By the time they soften, the base note is fully developed, and ideally helps to bolster the other notes. This is the scent left at the end of the day.
Understanding this symphony of interactions makes it easy to see why a perfume might smell nice when first applied, but can take on a stale or heady note by the end of the day. In this case, the base note of the fragrance is not to the wearer's liking. Conversely, a fragrance might smell better as the day wears on if the wearer's olfactory senses prefer the base note to the top and middle notes. When a person finds a fragrance that really appeals from morning until night, he or she has discovered a love for all three notes that compose the scent.
With all that people associate with these products, it might seem counter-intuitive that fragrant chemicals are generally caustic irritants in concentrated form. For this reason, fragrances are made with diluted essential oils and compounds. Generally, the concentration is about 20 to 40% for perfume, 10% less for parfum, 20% less for eau de toilette, and cologne only contains between 2 and 5% aromatic oils.
While flowers make up the largest source for chemical compounds used in commercial fragrances, bark, wood, resins, leaves, tobacco and citrus also contribute to the different categories of scents. Synthetic chemicals have also become popular and are more reliable from an industry standpoint, as they are consistent to work with, unlike natural products. The use of synthetic compounds is a new arena with an untested history in terms of health and the environment, however. Synthetic musk, for example, has been found in the Great Lakes due to nearby chemical processing. It has also been found in human fat cells and breast milk.
Shoppers who prefer to buy perfume that is made from natural compounds should look for the words "all natural ingredients." These products will likely be more expensive and may be harder to find. Ingredients listed as "imitation" or "natural synthetic compounds" refers to synthetic chemicals created to copy real-world chemicals. The synthetic version might have a much stronger odor than its more expensive, natural versions, but compounds it's made of are different elements than naturally occurring compounds and are not "natural."
While synthetic chemicals are increasingly used in traditional fragrance categories, they have also given rise to a new category of fragrances, grouped together under the heading of Ozone or Oceanic. This joins the existing categories of Floral, Fruit, Green, Wood, Amber and Leather, and Oriental.