Glycerol vs Propylene glycol: what is the difference?

How they differ

Both are viscous, sweet-tasting alcohols used to hold water in a product, and glycerol has one more hydroxyl group, C3H8O3 against C3H8O2. That extra group makes glycerol thicker and more strongly humectant, which is why it dominates in skincare, toothpaste and food glazes. Propylene glycol is thinner and a better solvent for flavour compounds, which is why it carries the flavour in e-liquid and in many oral medicines while glycerol supplies the visible vapour. Glycerol is also a real metabolic molecule: it is the backbone every triglyceride is built on, so the body has an established route for it. Both are widely permitted in food.

Side by side

Structural similarity 0.46 of 1, computed as a Morgan fingerprint Tanimoto coefficient. It measures shape, not effect.

Common questions

What is the difference between Glycerol and Propylene glycol?

Both are viscous, sweet-tasting alcohols used to hold water in a product, and glycerol has one more hydroxyl group, C3H8O3 against C3H8O2. That extra group makes glycerol thicker and more strongly humectant, which is why it dominates in skincare, toothpaste and food glazes. Propylene glycol is thinner and a better solvent for flavour compounds, which is why it carries the flavour in e-liquid and in many oral medicines while glycerol supplies the visible vapour.

Is Glycerol bigger than Propylene glycol?

Glycerol is the heavier molecule, 92.09 g/mol against 76.09 g/mol for Propylene glycol. Glycerol is C3H8O3 and Propylene glycol is C3H8O2.

Which has the lower reported LD50, Glycerol or Propylene glycol?

Glycerol, at 5,570 mg/kg (oral, rat), against 22,000 mg/kg (oral, rat) for Propylene glycol. An LD50 is one acute animal measurement, and the two here were not necessarily measured in the same species, so it is a data point rather than a ranking of how dangerous either is to a person.