The propylene glycol which makes up e-cigarette liquids tends to dry out the mucous membranes.nThis is the case for mouth and throat, which prompts us to recommend better hydration throughout the day.nThe eyes are also affected by the effects of PG and the irritation resulting in tearing, redness, itching is also linked to propylene glycol.nIt is then advisable to use artificial tears to overcome this side effect.