<P> Prolonged contact with propylene glycol is essentially non-irritating to the skin . Undiluted propylene glycol is minimally irritating to the eye, producing slight transient conjunctivitis; the eye recovers after the exposure is removed . Exposure to mists may cause eye irritation, as well as upper respiratory tract irritation . Inhalation of propylene glycol vapors appears to present no significant hazard in ordinary applications . However, limited human experience indicates that inhalation of propylene glycol mists could be irritating to some individuals . It is therefore recommended that propylene glycol not be used in applications where inhalation exposure or human eye contact with the spray mists of these materials is likely, such as simulated fogs for theatrical productions, or antifreeze solutions for emergency eye wash stations . </P> <P> According to a 2010 study by Karlstad University, the concentrations of PGEs (counted as the sum of propylene glycol and glycol ethers) in indoor air, particularly bedroom air, has been linked to increased risk of developing numerous respiratory and immune disorders in children, including asthma, hay fever, eczema, and allergies, with increased risk ranging from 50% to 180% . This concentration has been linked to use of water - based paints and water - based system cleansers . However, the study authors write that glycol ethers and not propylene glycol are the likely culprit . </P> <P> Propylene glycol does not cause sensitization, and it shows no evidence of being a carcinogen or of being genotoxic . </P> <P> Adverse responses to intravenous administration of drugs that use propylene glycol as an excipient have been seen in a number of people, particularly with large dosages . Responses may include "hypotension, bradycardia...QRS and T abnormalities on the ECG, arrhythmia, cardiac arrest, serum hyperosmolality, lactic acidosis, and haemolysis". A high percentage (12% to 42%) of directly - injected propylene glycol is eliminated or secreted in urine unaltered depending on dosage, with the remainder appearing in its glucuronide - form . The speed of renal filtration decreases as dosage increases, which may be due to propylene glycol's mild anesthetic / CNS - depressant - properties as an alcohol . In one case, intravenous administration of propylene glycol - suspended nitroglycerin to an elderly man may have induced coma and acidosis . </P>

Is propylene glycol an acid or a base