Propylene glycol irritation. I thought this was a rather benign ingredient?
I continue to study diligently as I have tackled a deodorant project with the help of a few amazing chemists on this site.
(Let me also say for the record, my formula does NOT contain PG.)
I started the project due to my personal lifelong irritation to commercial stick deodorants. I had suspected two potential irritants…. Sodium stearate, and a high rate of glycols used. Tonight’s reading from PubMed had the below paragraph in a larger document. My question is…. is PG generally accepted as an irritant in up to 3.8% of the population? Or is this simply due to the high concentration used in patch testing?
(I will link the article at the end…for those that want all the context.)
Propylene glycol, a solvent with moisturizing, antiseptic, and preservative properties, was the second most commonly present allergen and was present in 47 percent of the deodorants contained in the Walgreens database. It is used in a wide range of products, including cosmetics, food, toothpaste, and mouthwash, and functions in deodorants to stabilize the aqueous phase of the product. There is some controversy surrounding the allergic potential of PG. The NACDG found that 4.2 percent of patients referred for patch testing have a positive patch test to PG, but other studies have reported an incidence of positive reactions ranging from 0.1 to 3.8 percent.18 This large variability may be due to the fact that PG is a strong irritant (the Material Safety Data Sheet advises avoidance at concentrations over 50 percent11); therefore, patch testing may yield false-positive reactions. This irritant property of PG is particularly relevant to antiperspirants and deodorants, where long-term occlusion in the underarm area may contribute to the induction of irritant dermatitis.10 Currently, the NACDG uses 30 percent PG in water for patch testing, a concentration that has significant potential for skin irritation.19 At times, this irritation may be misinterpreted as contact dermatitis, leading to questionable data regarding true allergic potential of the product. To verify positive patch-test results, Funk et al suggest repeated patch test with serial dilutions, biopsies of affected skin, and oral challenge tests,19 but these methods are rarely used in the clinical setting. Propylene glycol is commonly found in deodorants at a concentration of 2 to 5 percent of product weight.20 This relatively low concentration may be below the elicitation threshold for some patients with PG allergy, but since it is difficult, if not impossible, to prospectively identify PG allergic patients who will tolerate PG-containing products and because their elicitation threshold may change over time, it is prudent to recommend that all patients with a positive patch test to PG avoid antiperspirants and deodorants containing this allergen