Spotlight On: Phenoxyethanol
Recently, a reader asked if phenoxyethanol was the same as ethanol. They are in fact, two distinct molecules. However, they do have some overlapping characteristics and uses. Since I covered ethanol quite extensively HERE, this post will focus primarily on phenoxyethanol.
What is phenoxyethanol?
Phenoxyethanol (PE) is an ethylene glycol ether (basically an ethanol molecule attached to a phenol group) that has a viscous or oily texture in its liquid state. In cosmetics, it is most-commonly used as a preservative, appearing in everything from bronzers to liquid foundations (1).
Rather than functioning as an antioxidant-type preservative that reduces the rate of decay, PE functions as an antimicrobial agent, which inhibits or even eliminates “challenging” doses of many variations of Gram-negative and Gram-positive micro-organisms (2). It’s also been shown to be effective against more common strains of bacteria, such as E. coli and Pseudomonas aeruginosa (3).
Is it safe?
If ingested in high concentrations, PE can certainly cause death. However, the scope of this post will be limited to the topical application of standard concentrations (<1.0%) of PE.
In the ethanol post, I discussed whether or not it was significantly metabolized to acetaldehyde in the skin, and if any meaningful amount was systematically absorbed through the skin. Similarly, these two aspects must also be examined for PE. On intact human skin, out of five glycol ethers including ethanol, PE had the highest rate of metabolism to its corresponding acetic acid (ethanol had the lowest rate) (4). If the metabolism pathway of PE is anything like that of ethanol, the next metabolite could be some form of acetaldehyde, which is highly unstable and if not quickly converted to (phenoxy)acetic acid, can generate free radicals.
But before you panic, as we learned in the retinol metabolism post HERE, which also involves the same family of enzymes responsible for PE metabolism, this conversion process occurs below the stratum corneum. Therefore, we need to see what amount of PE is absorbed systematically or basically into the dermis. According to this study that tested absorption of an occluded water-based product containing PE and another antimicrobial, the amount of 2% PE absorbed into porcine skin, which of the tested surfaces is most comparable to human skin in terms of permeability, was only 1.4% after 6 hours and 11.3% after 28 hours (5).
These studies suggest that at <1.0%, the rate of absorption and conversion of PE to potentially harmful intermediates and metabolites, is very low. In fact the exact same product from (5), was tested on premature newborn infants that were <27 weeks old, and the result corresponds to those found in (5). The study demonstrated that, “In contrast to alcohol-based antiseptics, an aqueous solution of … 2-phenoxyethanol does not cause major skin damage… 2-Phenoxyethanol is readily absorbed by the newborn’s skin but apparently undergoes extensive oxidative metabolization to 2-phenoxyacetic acid” (6). The conclusion substantiates the theory that PE has the highest rate of metabolism in skin, while also triggering no measurable damage. If babies can handle it, so can adults.
So how DOES PE compare to ethanol?
While PE metabolism occurs more frequently than ethanol metabolism in the skin, the amount of PE allowed in topical products (<1.0%), is significantly lower than that allowed for ethanol. Therefore, the two balance each other out in this particular aspect. Since the stratum corneum prevents significant absorption of both molecules, any free radicals that are generated will most likely be equal or less than those generated from everyday autoxidation reactions. On a plus side though, due to the phenol group present in PE and consequently its “oily” texture, it evaporates and dries out the skin less severely than ethanol, as witnessed in (6).
Phenoxyethanol (PE) is a safe and efficacious preservative that is used pervasively throughout the cosmetics industry, second only to parabens. And while I believe that the use of parabens is also safe, if you’re interested in paraben-free products, look for ones that use PE!
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About the author: John Su is an established skin care expert and aspiring dermatologist. He also runs a blog, The Triple Helix Liaison, dedicated to providing unbiased, meaningful, and insightful information about skin care. For his full bio, please visit our About Page.