Aldehydes are organic compounds with a carbonyl group that is bonded to at least one hydrogen. The general notation for an aldehyde is RCHO, where R is hydrogen or an alkyl or aryl group. Aldehydes are found in low levels in some essential oils, such as in citrus peel oils. Many aldehydes have a characteristic fatty odor, and many used in perfume have a sparkling or fizzy character. Chanel No 5, introduced in 1921, is famous for an overdose of aldehydes, but it was not the very first perfume to use them. Although floral aldehyde perfumes became popular after Chanel No 5 was released, they now have a vintage vibe to many people because they have not been as common in recent years as the clean scents, gourmands, and fruity florals that have dominated recent new releases.

The iconic Chanel No 5 bottle is shown.