One of the most magical things about perfumes is their potential to age like a fine wine. An integral part of crafting a perfume is the maturation process, during which all of the components of the perfume formula integrate fully with the carrier (whether alcohol or oil). I try to age as many of my formulas as possible before dispatching them. The maturation process ensures that the final form is the same as my early vision for it, gives me a better representation of how the fragrance will continue to perform with age, and eliminates the need for the collector to “rest” the perfume on receipt. Perfumes should only need to be rested for a few days if exposed to an elemental shock such as extreme temperatures or excessive jostling in transit. Perfumes that you receive shortly after a limited edition re-stock will not have had as long of a maturation process, so they may benefit from resting for a bit longer.
When perfume materials are suspended in a base with a long shelf life, they tend to bloom beautifully over the months and years. Pure perfumers alcohol without excess additives is ideal for aging alcohol-based fragrances, and carrier oils with a very long shelf life are perfect for perfume oils. Some perfume types do better with aging than others. Rich resinous, woody, earthy, and some musk blends will usually age better than lighter fruity, green, or floral blends. Top notes will be the first to burn off during the aging process, and over the course of a few years, the top notes could fall away entirely or integrate in interesting ways with the base and heart notes. The base and middle/heart notes often end up blooming and darkening in this process, creating more depth. Because I enjoy working with dark atmospherics, I love the way many of my favorite materials like resins and deep woods age. A bottle of Boneyard acquired ten years ago will smell quite different from a bottle acquired recently.
Temperature and light can significantly affect the longevity and aging of perfumes. The optimal environment for fragrances is a cool, dark, dry area. Always store your perfume away from light and extreme temperatures to help them age well. Keeping them in amber or darker colored glass bottle will also protect them more than storing them in a clear bottle. Also, you shouldn't ever store perfume in your bathroom since the humidity levels can affect them.
The aging process does interesting things to perfumes. Some go off and end up smelling unpleasant, but many retain their signature aura, even if the overall composition has changed somewhat. Some bottles of Shalimar from the 1920s, vintage Chanel, and other classics still smell divine decades later, even if they have suffered some degradation of their top notes. Alcohol-based perfumes will have greater longevity than oil-based ones, but I have perfume oils that have been aging for over a decade that still smell wonderful. If you detect an unusual undertone that smells pungent, waxy, or similar to stale cooking oil, this is a good indicator that the oil has lived out its life. Separation of ingredients is also an indicator that the perfume has expired, but you can only detect this in clear glass, so let your nose be the arbitrator in the case of older darkly colored bottles.
To ensure the long life of your perfumes, be sure to keep them in minimal contact with light, heat, air, and humidity and be sure to keep them in a cool, dark place to ensure they live up to their full potential as the years go on.