Fragrance is a combination of chemicals that gives some products their scent. It can come from natural sources like plants, flowers or foods, or it can be synthetically manufactured as found in scented household products such as perfumes and colognes. Fragrance ingredients can include a wide variety of chemical components including petrochemicals, solvents, stabilizers, UV-absorbers and preservatives. These ingredients are usually listed on the label with a generic term like “fragrance” and can contain a wide range of skin allergens including linalool, hexyl cinnamal, and geraniol.
Today, many perfumers choose to use synthesized odorants in addition to the more traditional natural plant based ones. This allows them to add fragrances that are not available naturally or that would be too expensive to harvest from a natural source. For example, the ozonous metallic marine smell of seaweed can be reproduced with a synthetic compound called calone, while coumarin and orchid scents can be made with other inexpensive man-made chemicals.
The earliest forms of perfume were alcoholic solutions called parfums, or essences, that were highly concentrated. They were mixed with a variety of ingredients and the scent was emitted by applying a few drops to the skin. Modern perfumes are often more heavily diluted with water or alcohol. Perfumes are typically divided into three structural parts — top notes, middle notes and base notes. Top notes are the light fresh scents that evaporate quickly, such as citrus or floral scents. Middle notes are the heart of a perfume, and they are usually a blend of several flower scents. Base notes are the deep, rich and long-lasting scents that appear close to when the middle notes start to disappear from the nose.