Presence/Absence of Propylene Glycol in Commonly Used Topical Products in the Dermatology Clinic

To the Editor,

Propylene glycol (PG) is a clear, colourless synthetic liquid used in cosmetics and medications as a solvent, humectant, emulsion stabilizer, antimicrobial agent, skin-conditioning agent, and viscosity-decreasing agent. ¹ It is also found in many prepackaged foods, condiments, and other foods. ² In 2018, PG was named the American Contact Dermatitis Society’s (ACDS) Allergen of the Year. ² Although the significance of PG as a contact allergen has been debated, ¹ it has been associated with causing allergic contact dermatitis, irritant contact dermatitis, and even systemic contact dermatitis. Due to its many functions, there has been an increase in its presence in personal care products and medicaments. ² According to the 2016 CAMP system (Contact Allergen Management Program, a database of products and their ingredients maintained by ACDS), PG is found in 37.8% of 4674 products. ²

In patients with a positive patch test to PG, finding PG-free prescription or common over-the-counter (OTC) products for a variety of dermatologic conditions can be time-consuming and cumbersome, as it requires the physician to review each prospective recommended product’s monograph to check for the presence or absence of PG. Accessing the CAMP database provides one solution to this challenge, but the database covers products available in the United States, and does not include many Canadian prescription drugs. In addition, many general dermatologists do not have easy access to the CAMP database. As well, there can be significant differences in OTC drugs between the 2 countries. As one approach to solving this problem, we sought to create a list of Canadian prescription and OTC products used for common skin conditions in the dermatology clinic, with clear indication which did/did not contain PG (see Supplementary Material for tables of commonly used topical products containing and not containing PG). We did not include topical corticosteroids in our review since there was a recent comprehensive review of this topic by Roberts and de Gannes. ³ To accomplish our goal, we reviewed the product monographs found in the Health Canada Drug Product Database, ⁴ looking for the presence of PG and its common synonyms (methyl glycol, trimethyl glycol, 1,2-dihydroxypropane, 1,2-propanediol, propane-1,2-diol, 1,2-propylene glycol ¹ ). Since there is cross-reactivity between PG and butylene glycol, ⁵ we also noted if there was the presence of the latter. Although we specifically categorized all products listed as either containing or not containing PG, we chose to include the entire list of non-medicinal ingredients, since these may also have relevance for other contact allergies. After initiating this endeavour it became clear that to cover all OTC medications was beyond the scope of this article, therefore we chose to emphasize the prescription drugs, whereas for the OTC products we focused on a subset, mainly the original formulations [eg, Polysporin Original cream (contains PG) and ointment (does not contain PG), etc.]. It is important to note however that this segregation between creams and ointments vis-a-vis presence or absence of PG does not hold with all product lines. Similarly, the assumption that the absence or presence of PG in generic products would follow that of the original branded products does not necessarily hold true.