Aldehydes are synthetic aliphatic fragrances that, when used alone, have a sticky, fatty smell that lingers in the nose. There are multiple types of aldehyde fragrances, including citrus, green, and floral, and they are used differently depending on the fragrance they are intended for. The most famous perfume that uses aldehydes is Chanel No. 5. At the time, women's perfumes were generally soft, powdery floral types that mainly used natural fragrances, but No. 5, which boldly used aldehydes, was an innovative scent. Aldehydes are not exactly pleasant to smell on their own, but when added to perfume, they can give an urban, sophisticated impression.