So what is the big fuss about PG found in cosmetic products all about??

A study was conducted by a dermatologist from the North American Contact Dermatitis Group (NACDG) and the results shown that repeated exposures to propylene glycol for a short time may cause irritation and allergies. Using the database, they analyzed the number of products containing allergens. According to Table 1, Propylene glycol is found to be the second most commonly present allergen in deodorants and antiperspirants. It is found in 47% of the deodorants and antiperspirants of the database, at a concentration of 2 to 5% of the product weight. This low concentration of propylene glycol is unable to elicit the irritation for patients with Propylene glycol allergy. However, it is recommended to avoid deodorant and antiperspirant with Propylene Glycol, as exposure over time may change the elicitation threshold, and thus causing dermatitis.

Though cancer might not be a concern (according to the Cosmetic Ingredient Review Expert Panel), it was found that Propylene Glycol can provoked allergic reactions in patients with eczema and other skin allergies, even in formulations of much less than 50%.

In addition, the Material Safety Data Sheet (MSDS) cites skin, liver and kidney damage that can result from contact with PG, and it gives safe handling instructions, calling it a hazardous substance. Though not specified, this is for the more concentrated industrial grade.

On the other hand, studies done in vitro tests on mammalian cells revealed that some cells underwent mutation when contact repeatedly with PG.
In Europe, where the authorities are much more cautious about what is allowable in cosmetics and foods, propylene glycol is limited to mostly non-food uses.