Essential oils haven't changed much over the millennia, but the way in which they are diffused has.
The process of dispersing incredibly aromatic oils like Bergamot into the environment has developed over the centuries from simple to sophisticated. You don't need a qualification in chemistry or physics to understand how aromatherapy diffusers work.
You will find it helpful, though, to know the ins and outs of how each different type of essential oil diffuser works. Once you do, you'll be able to choose the right diffuser for the surroundings you want to use it in.
How different types of essential oil diffusers work
Evaporation is when warmth in the atmosphere causes moisture to turn into vapour. It's a mostly invisible process that occurs with everything from puddles after a rainstorm to the waters of the ocean as they're heated by the sun. Basic essential oil diffusers work the same way - by evaporation.
A common example of an essential oil diffuser that works by evaporation is a reed diffuser. You've undoubtedly seen them next to cans of air fresheners on a shelf in your local store - lots of thin sticks of porous wood in a small glass container of essential oil. Insert the sticks into the oil, and they'll start to soak it up. Heat in the room causes the oil that has seeped to the top of the sticks to evaporate and perfume the air.
As you might guess, the way a reed diffuser works is not a very controllable operation. The warmer the room, the faster the oil will evaporate. Have your central heating on full blast, and you'll soon discover there'll be nothing left but dry twigs and an empty bottle collecting dust because it no longer smells, and you've forgotten it's even there.
Although evaporative aromatherapy diffusers work by the same principle of evaporation, they're a little more technologically advanced. Contained in the base of the diffuser is a small battery or electric fan. The fan generates a gentle breeze inside the diffuser which blows through a pad you soak with essential oil. The movement of air through the pad causes the oil to evaporate. The main advantage of an evaporative essential oil diffuser over a reed diffuser is you can switch it on and off anytime you like.