In the broadest sense, all products that are designed to make a person smell a certain way can be called "perfumes." However, in the cosmetic industry, perfume has a specific meaning. Perfume, eau de parfum, eau de toilette, eau de cologne and aftershaves are not the same thing.
Perfume extract (occasionally simply known as "perfume") has the highest concentration of aromatic compounds, and as such, is generally the most effective. It is also the longest-lasting and has a very strong scent, therefore only small amounts should be applied. Like all fragrances, perfume consists of aromatic compounds that are mixed with alcohol and water to dilute them. Not doing so would cause the scent to be overpowering to the point of being extremely unpleasant. It should be noted that people with sensitive skin can have a reaction to any fragrance, but perfume is by far the most likely to cause one.
Eau de Parfum
Eau de parfum, parfum de toilette, or eau de perfume (EdP) contains less perfume oil than perfume extract. It is also less likely to cause allergic reactions. Most eau de parfum fragrances have less than twenty percent aromatic compounds, but as the term is not regulated, the exact percentage will vary from company to company.
The key advantage to eau de parfum is the price. Because it uses much less perfume oil than higher-grade perfume, the cost is that much less. Unlike other types of fragrance, such as eau de toilette or eau de cologne, it can be used in the same way as perfume extract. Both eau de parfum and perfume extract should be dabbed on warm spots of the body, especially behind the neck and on the wrists, as the heat will help the scent to spread. Using the others in this way causes the product to dissipate too quickly. It also lasts longer than eau de toilette or cologne, and is less likely to cause skin reactions than perfume.
While it lasts longer than other products, eau de parfum is still unlikely to last as long as perfume extract. While the scent will remain several hours later, it will not have nearly the same strength that the perfume would have had. Moreover, while eau de parfum is less expensive than perfume, it is still more expensive than eau de toilette and cologne, which have even less aromatic oil. Finally, the eau de parfum may not have the exact same scent as the perfume it is meant to resemble. It is not always created simply by watering down existing perfume, but instead by mixing different essential oils to create a similar scent.
As discussed above, eau de parfum is less likely to cause allergic reactions, but it still may cause them. People with sensitive skin should use eau de parfum sparingly. Secondly, using large amounts of the product will not cause it to last longer, but simply to be overpowering as long as it does last. Finally, it should be noted that perfume extract, eau de parfum, eau de toilette, and eau de cologne are not regulated terms. They simply describe how much perfume oil is in a product relative to the other products, in descending order (extract has more than eau de parfum, eau de parfum has more than eau de toilette). Within a single company, this can be an effective guideline, but between companies, it is not. An eau de toilette from one company may contain more perfume oil than the eau de parfum from another.