While propylene glycol should actually be avoided for some people, it's not for the scary reasons you might have read about online. Because propylene glycol is derived from petroleum, many people fear it is carcinogenic and may be toxic when used in skin care products. But cosmetic grade vaseline, unlike commercial petroleum, does not cause cancer, and neither does propylene glycol, according to Zeichner. Herrmann added: "Many safe products and chemicals can be extracted from the toxic parent, but what is important for safety is the final chemical form. She continued, "Extracting oil from it doesn't make it dangerous unless pollution is a problem. In its final form it is considered non-carcinogenic and is present in many topical cosmetics."

While these more serious claims don't make sense, propylene glycol isn't entirely harmless. As Herrmann pointed out, it was the Allergen of the Year for the American Contact Dermatitis Association in 2018. 3 "If you get a red, itchy rash where you use the product, you may be allergic to one of the ingredients," Zeichner says. "Propylene glycol is often the culprit." Herrmann adds that people with eczema may be more sensitive to the ingredient, and for those patients, she always recommends doing a patch test or trying a new product on a small patch of skin on the inside of the wrist before using it more widely.

However, in general, products containing propylene glycol are suitable for most people. "Based on what we know today and how it's been used in cosmetics for years, propylene glycol is a safe ingredient as long as you're not allergic to it," Zeichner said.

How to use it

As Herrmann explains, because propylene glycol is found in many products, there is no one way to use it. Instead, she recommends using products with the ingredient as directed by a dermatologist or as directed by the manufacturer. As for how often or how much you should use, Hellman says propylene glycol is considered safe, even when consumed in relatively large amounts.