Essential oils are comprised of many types of aromatic molecules, also known as constituents. There can be a hundred or more constituents that are naturally present in an essential oil.
Some constituents weight more than others. The lightest constituents, often referred to in perfumery as top notes, evaporate the fastest. The heaviest, known as base notes, tend to evaporate the slowest.
Over time, the aroma of an essential oil changes as the different constituents evaporate. Therefore, it can be helpful to assess the aroma of an essential oil over time instead of solely after initial application.
If you have the same botanical type of essential oil from different suppliers, it can be useful to evaluate the aroma simultaneously by using a different fragrance testing strip for each oil. You can then do a comparison as time passes.
Fragrance Testing Strips are also known Scent Strips and Fragrance Blotters. Fragrance Testing Strips tend to be constructed of thick white paper and are often (but not always) about 6" long and have a unique paddle shape.
Have you ever gone to someone's home for dinner and immediately noticed the delicious aroma wafting from their kitchen? At first, the aroma smells strong. Then over time, you adapt to the aroma and begin to barely notice it, even if you try. This is referred to as olfactory fatigue, sometimes also known as olfactory adaptation. A similar temporary phenomenon occurs when smelling numerous aromatics within a short interval of time. You're no longer able to fully distinguish an essential oil's aroma or easily distinguish one essential oil from another. Therefore, it's best to only assess one or two essential oils at a time.
Take frequent breaks to minimize the risk of encountering olfactory fatigue during aromatic evaluations. Smelling coffee beans can be helpful in minimizing olfactory fatigue.