You might think that the difference between cologne and perfume is based on gender. The truth is that the difference lies in the concentration of essential oils in the fragrance's water and alcohol base. Perfumes contain a higher concentration of oils, typically around 20 to 30 percent, while the oil concentration in cologne is around 2 to 4 percent. Other types of fragrances such as eau de toilette and eau fraiche fall on the same oil-concentration spectrum. This concentration determines how long the scent lasts and when to use it.
Eau fraiche contains the lowest concentration of fragrant oils, typically in the range of about 1 to 3 percent. Many aftershaves fall into this category. Once applied, the scent wears off in about an hour.
When you spray or dab on a fragrance, you first smell its top notes, the scents that diminish quickly, typically within minutes. Because eau fraiches wear off quickly, your body chemistry doesn't have much time to interact with the oils in a way that notably alters the scent, for good or bad, the way that they do with more intense fragrances.
Eau de Cologne
Eau de cologne, or simply cologne, contains an oil concentration of 2 to 4 percent. The term is commonly reserved for light and fresh masculine scents, which are often fruity or musky and typically last a few hours. During the first hour, the middle notes that are the heart of the fragrance prevail. During the second hour, the base notes that comprise a fragrance's body take over. This is called the dry-down period, and it's when your body chemistry interacts with long-lasting fixatives to produce the true or final scent. Since eau de cologne has a lower concentration, the scent does not last as long, so you may need to reapply if you go out for after-work drinks or dinner.
Eau de Toilette
In an eau de toilette, the concentration of fragrant oils is about 5 to 15 percent, and the scent wears off in about three hours. The final few hours are the dry-down period when the final scent prevails. This final scent is determined by a variety of factors, such as your skin type, diet, hormone levels, other products used, sweat, and even the climate. These can greatly affect the final scent, for good or bad, so it's a good idea to ask a friend to give you a frank opinion after a few hours.
Eau de Parfum
Eau de Parfum is often simply called perfume. However, that's somewhat of a misnomer. Eau de parfum, with a fragrant oil concentration of 15 to 20 percent, contains less oil than perfume, and it lasts five to eight hours. These intense scents can sometimes give rise to a misleading array of top notes when initially applied. With a dry-down period that lasts up to seven hours, the final scent is greatly affected by your body chemistry, which in turn can change dramatically over the course of an evening, depending on your activities. Keep this in mind and pay attention to the way your scent changes throughout the day to ensure you like the scent as much at the end of the day as you did at the beginning.
Perfume is the most intense fragrance commonly used, with a concentration of 20 to 30 percent. Also referred to as parfum, it can last as long as 24 hours after a single application. During this time, your body chemistry can change dramatically, so the final scent typically does as well. This highlights the importance of asking honest friends for their opinions as you seek the best perfume to make the desired statement.