Perfume oil is always diluted with a solvent as pure oils contain high concentrations of volatile elements that may lead to allergic reactions and probably injury when applied to the skin or clothing. Solvents also assist the perfume oils by diffusing them into the air. Most of the time perfume and fragrance manufacturers will use Ethanol or a combination of air and ethanol. Dilutions of the scent oil may also be produced using solvents such as jojoba, fractionated coconut oil or wax.

Different perfumeries or scent houses allot different amounts of oils to all of their scents. Therefore, though the oil density of a perfume in eau de parfum (EDP) dilution will always be higher than the same perfume in scent (EDT) form in the same range, the actual amounts can alter between perfume houses. The cost of a perfume is directly related to its concentration, with the least diluted being the most expensive formulation of the smell. 
 

The following shows the standard concentration levels of perfume oil as well as estimated period of effectiveness for each fragrance type.