How common are side effects with propylene glycol in vaping solutions?

The side effects of propylene glycol are rare because it does not form harmful crystals on the skin. However, it only causes irritation if the skin if exposed to it frequently, as stated by the Agency for Toxic Substances and Disease Registry (ATSDR).

Propylene glycol is a synthetic liquid used in absorbing water and making polyester materials. It is also used as an ingredient is food, chemicals and pharmaceutical products. People are usually exposed to propylene glycol when eating food or using cosmetics that contains it. However, the exposure level is usually low. Exposure to mists and artificial smoke made from propylene glycol is usually high, as stated by ATSDR.