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Answer by Tatiana Estévez, ex-aromatherapist, and I make my own perfumes:
The base of any fragrance you can buy in shops will be the "perfume essence"—what actually makes the smell. This is a combination of essential oils (cedar wood, lime, sandalwood, etc), absolutes (jasmine, rose, neroli), animal extracts (musk, ambergris), and synthetic fragrance (this could be nearly anything).
This base perfume essence would actually not be that attractive by itself and in some cases would be actually unpleasant. It is too concentrated, so it needs to be diluted, and this is done with alcohol and water.
Fragrances come in many forms and have many different names but generally the main four categories are as follows:
Perfume: The perfume you see in the store is not the pure perfume essence and has been diluted. However, it is the most concentrated of all the fragrance options, and it is the most expensive for this reason. It tends to be slightly oilier and will typically contain 15-40 percent pure perfume extract. It has a slightly thicker, oilier consistency. It tends to be sold with "stopper bottles" and not sprays. It is too strong to spray all over (and too expensive).
The percentage of pure perfume extract is not necessarily an indicator of the quality of perfume, though. As mentioned, there are many essential oils that you wouldn't want to smell like in small doses. Real musk and ambergris are expensive and not pleasant in their pure forms, so a single drop can dramatically increase the price of a perfume, but you wouldn't want more than that single drop.
Eau de perfume/parfum: This uses the same perfume essence but less of it and more alcohol and water. This means the smell is a bit lighter and usually doesn't last quite as long, but as it is a bit lighter, many find this preferable. It is of course cheaper. Typically there will be 10-20 percent perfume essence in eau de perfume. This perfume might be sold in normal bottles or sprays, but if a spray is used, it shouldn't be just doused all over.
Eau de toilette: This is lighter still and usually sold in spray bottles. The lightness of it makes it more suitable to spray more liberally. The high alcohol content means it will not last very long. Generally, this version is the most advisable to use day to day, as it is less intense, and even if you do use too much it will lighten up fairly quickly. Typically there will be 4-15 percent pure perfume.
Eau de Cologne: Cologne is an abbreviation of eau de Cologne for the city of Cologne, Germany, where a particular scent was first made; hence it was a water from Cologne. There are specific blends of fragrances that fall in this particular category of eau de Cologne; they are very light, fresh, and fruity, and they contain the essential oils, lemon, bergamot, orange, and the absolute neroli. They may also contain the essential oils lavender and rosemary.
These days, though, eau de Cologne is also used to determine the most diluted version of the perfume, typically 2-5 percent. These are rarely used in expensive perfumes but tend to be more splash kind of perfumes or fragrances for younger people.
Note: The percentages I have given for perfume essence compared to total product are just guidelines. There is no universally agreed ratios, and they will vary from source to source.
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