Perfumes with natural ingredients often smell different in batches based on the source of the ingredients, while synthetic ingredients usually have consistency in their smell and last longer. Perfumes are often designed with top, middle and base notes, and designed to smell different based on the time after application. For example, some top note citrus scents smell stronger immediately upon application, while a lavender middle note may be sensed after some time from the application as the top note evaporates.