From the Mayo Clinic:
https://www.mayoclinic.org/drugs-supplements/glycerin-oral-route/precautions/drg-20067747?p=1
The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:
Type 2 diabetes mellitus—Use of glycerin may increase the chance of dehydration (loss of too much body water)
Confused mental states or
Heart disease or
Kidney disease—Glycerin may make these conditions worse
That is one route for using it, and they found that approach greatly helped.
However, direct application to the skin worked similarly.