Repeated oral exposure to propylene glycol in a short time can sometimes produce skin irritation, notes the Agency for Toxic Substances & Disease Registry. There is little information available on the effect of propylene glycol inhalation on the lungs. Inhaled propylene glycol can enter the bloodstream and is typically broken down in the body in 48 hours.
Propylene glycol is almost completely odorless and tasteless, and appears as a syrupy liquid at room temperature. Propylene glycol inhalation can result from the use of e-cigarettes or from inhaling the mists produced by e-cigarettes, states Dina Fine Maron for Scientific American. It is a common ingredient in artificial smoke machines that produce a vaporized form that can be inhaled. Propylene glycol is used in many substances to allow them to absorb water and maintain moisture. Propylene glycol is commonly found in many foods, drugs and cosmetics, and exposure to this substance is highly likely, according to the Agency for Toxic Substances & Disease Registry.
Propylene glycol is generally recognized as safe; however, the World Health Organization has determined it should not be consumed in excess of 25 milligrams per kilogram of body weight, explains the Agency for Toxic Substances & Disease Registry. Exposure may be more intense when the vaporized form is introduced to enclosed spaces.