This questions seems to get asked a gazillion times around the interweb. As usual, The Beauty Brains comes through with a solid, and scientific-based answer:
CYW says…I always get confused about glycerin. Is it an ingredient I should use to combat my frizzy hair on hot, humid days? If so, how much can I add to my leave in conditioner so it will be affective without being sticky.
Glycerin is what is known as a humectant.. That means it has the ability to absorb moisture from the air. This is a very helpful property in skin lotions where it can help bind moisture to the skin. However, since humidity tends to increase the frizzing of hair, binding additional moisture is the last thing you want to do. I would stay away from glycerin in a leave in conditioner to be used under high humidity.
There is one possible exception: certain types of African American hair which are extremely dry may still benefit from glycerin even in high humidity.
The question of whether glycerin can take moisture away from your hair when used in winter comes up just as frequently. Jc, materials scientist of The Natural Haven Bloom, breaks this one down here in a fact-based, yet easy to understand way. Jc also offers troubleshooting for working with glycerin in hair care recipes.
Moral of the story: Glycerin is your friend…when you treat her with care and sensitivity like the delicate damsel that she is.