Concentration

Perfume oil is necessarily diluted with a solvent because undiluted oils (natural or synthetic) contain high concentrations of volatile components that will likely result in allergic reactions and possibly injury when applied directly to skin or clothing. Solvents also vaporize the essential oils, helping to diffuse them into the air.

By far the most common solvent for perfume oil dilution is ethanol or a mixture of ethanol and water. Perfume oil can also be diluted by means of neutral-smelling lipids such as jojoba, fractionated coconut oil or wax. The concentration by percent/volume of perfume oil is as follows:

Perfume extract: 20%-40% aromatic compounds
Eau de parfum: 10-30%aromatic compounds
Eau de toilette: 5-20% aromatic compounds
Eau de cologne: 2-5% aromatic compounds

As the percentage of aromatic compounds decreases, so does the intensity and longevity of the scent created. Different perfumeries or perfume houses assign different amounts of oils to each of their perfumes. Therefore, although the oil concentration of a perfume in eau de parfum (EDP) dilution will necessarily be higher than the same perfume in eau de toilette (EDT) form within the same range, the actual amounts can vary between perfume houses. An EDT from one house may be stronger than an EDP from another.

Furthermore, some fragrances with the same product name but having a different concentration name may not only differ in their dilutions, but actually use different perfume oil mixtures altogether. For instance, in order to make the EDT version of a fragrance brighter and fresher than its EDP, the EDT oil may be "tweaked" to contain slightly more top notes or less base notes. In some cases, words such as "extrême" or "concentrée" appended to fragrance names might indicate completely different fragrances that relates only because of a similar perfume accord. An instance to this would be Chanel‘s Pour Monsieur and Pour Monsieur Concentrée.

Eau de cologne (EDC) was originally a specific fragrance of a citrus nature and weak in concentration made in Cologne, Germany. However in recent decades the term has become generic for a weakly concentrated perfum of any kind.