The intensity of the fragrance, and how long it lasts depends on a perfume's concentration, as well as the intensity of the perfume oils used.
Perfume oils need to be diluted in a solvent, typically alcohol (ethanol) or a mix of water and ethanol, as undiluted oils can cause allergic reactions & skin irritation. Also, undiluted perfume oils would have unpleasantly strong aromas.
The concentration (%/volume) of perfume oils in EDT and EDP are as follows:
- Eau De Parfum (EDP): 10-20%, on average 15% perfume oils
- Eau De Toilette (EDT): 5-15%, on average 10% perfume oils
Due to the higher concentration of perfume oils in EDP, their fragrance is more intense and longer lasting when compared to the EDT, and thus, is more expensive comparably.
It is also because of this, that you can rarely find Men's Fragrances in EDP concentration.