While I've heard of putting essential oils in the belly button, personally I've never tried it...until recently. Now that I have, I must say -- why didn't I ever do this before??!!
Essential oils only take about 20 minutes to get into the bloodstream through our skin. There is thought to be a 'gland' called the Pechoti in the belly button, although there is no actual evidence of this.
This 'Pechoti Method' is derived from the Ayurvedic medicinal practice in India, which focuses on the connection between the physical & the spiritual health. While I won't go into the actual biology of weather the belly button continues to function after the umbilical cord is severed, there is evidence that there are multiple veins still in tact & while they might constrict, they do not become obsolete, rather they are connected to almost every organ of the body.
Just because no evidence of this gland has been actually found, there's many beneficial factors that can be attributed to applying essential oil into one's belly button, even CBD oil. A couple drops of a good therapeutic essential oil...diluted....then massaged into that area certainly can't hurt. One doesn't want to push too hard on that area as there a a large amount of nerves in that region.
This simple method can enhance digestion, calm the mind (especially if one uses lavender),is able to reduce joint pain and it can improve reproductive health.
Some practitioners consider the belly button a 'reset' button and one can treat almost any physical or emotional ailment through this. Some contend it stimulates that all important vagus nerve (which is a topic for another discussion).
So weather or not there is proven scientific evidence this works, why not try it. Either a nourishing carrier oil or essential oils, using with caution, what can it hurt???