Aromatherapy diffusers need cleaning on a regular basis.
It is best to consider your individual diffuser and read and follow the instructions you have from the manufacturer.
Here is how I clean my diffusers. I usually empty out the water, wipe them with a tissue and use a cotton bud to carefully wipe into any nooks and crannies. I then use a little white vinegar with some water (as below) and run the diffuser (have the window open) for about 5 minutes and then rinse out again with clean water.
If you do not have your own diffuser and would like one please contact me. I work with doTERRA products and am a Wellness Advocate for them.