Propylene glycol (PG) is a simple organic alcohol widely incorporated into thousands of cosmetic and food products, including many deodorants and antiperspirants. Its inclusion often sparks consumer questions regarding its safety, particularly when the ingredient is associated with industrial uses like antifreeze. This article examines the scientific evidence concerning the use of propylene glycol in underarm hygiene products to address consumer concerns about potential health effects and localized skin reactions.
The Role of Propylene Glycol in Deodorant
Propylene glycol, also known as 1,2-propanediol, is a synthetic alcohol that functions as a multipurpose ingredient in deodorant formulations. The molecule is a clear, viscous liquid with the chemical formula \(\text{CH}_3\text{-CHOH-CH}_2\text{OH}\). Its primary purpose in stick deodorants is to act as a solvent and vehicle, ensuring that active ingredients like fragrances and odor-neutralizers are uniformly dispersed.
In solid stick formulations, PG is combined with a gelling agent, such as sodium stearate, to create a firm, smooth base that allows for easy application. It also acts as a humectant, drawing moisture to itself, which helps prevent the product from drying out and contributes to a smoother feel on the skin. PG concentration can vary significantly, sometimes constituting up to 50% of the formulation base, or used in smaller amounts for its preservative and stability functions.
The high purity grade of PG used in cosmetics and pharmaceuticals is distinct from the industrial-grade version used in antifreeze applications. Cosmetic-grade PG is approved as a food additive and used as a solvent in many oral and topical medications. Some manufacturers source PG from vegetable glycerin, using a catalytic process to create a plant-derived version of the identical chemical compound.
Systemic Safety: Scientific Consensus on Toxicity and Absorption
A primary concern is whether applying propylene glycol to the underarm area leads to internal exposure or long-term health risks. Scientific reviews have consistently determined that the compound is nontoxic and noncarcinogenic at the concentrations found in personal care products. The U.S. Food and Drug Administration (FDA) includes PG on its list of substances Generally Recognized As Safe (GRAS) for direct addition to food.
When applied topically, propylene glycol has very limited dermal penetration; the molecules do not readily pass through the upper layers of the skin to reach the bloodstream in significant amounts. Any small amount that is absorbed is efficiently metabolized by the body. Propylene glycol is converted into lactic acid, a substance naturally produced by the muscles during exercise.
The Cosmetic Ingredient Review (CIR) Expert Panel, an independent scientific body, has concluded that propylene glycol is safe as used in cosmetic formulations, provided the final product is nonirritating. Concerns regarding long-term systemic effects like cancer or reproductive harm are not supported by regulatory and scientific consensus. The exposure level from daily deodorant use is vastly lower than the doses required to cause systemic issues in clinical or industrial settings.
Dermal Reactions and Skin Sensitivity
While systemic health risks are low, propylene glycol can cause localized issues for a subset of the population because it is a known irritant and a weak contact allergen. The irritation is confined to the area of application and is not indicative of internal toxicity. This localized reaction is the main reason PG has a negative reputation.
Propylene glycol is one of the common causes of allergic contact dermatitis in cosmetics. Symptoms of a reaction may include localized redness, itching, a burning sensation, or a rash. Although it is considered a weak sensitizer, irritation can occur at concentrations as low as 2%.
Contact allergy to propylene glycol is uncommon in the general population, estimated to be present in up to 3.5% of individuals patch-tested for suspected contact dermatitis. Individuals with pre-existing skin conditions, such as eczema or atopic dermatitis, may be more susceptible to irritation from PG. Dermatologists can confirm sensitivity through patch testing, which involves applying a small amount of the substance to the skin under controlled conditions.
Options for Avoiding Propylene Glycol
For individuals who experience sensitivity or prefer to avoid propylene glycol, many effective alternatives are available. The most common substitute used in “natural” or PG-free deodorants is 1,3-propanediol, often listed simply as Propanediol. This ingredient is chemically related to PG but is derived from renewable sources like corn sugar and is considered less irritating to the skin.
Other popular alternatives function differently to create a solid base or deliver moisture, including vegetable glycerin (a humectant) or various natural oils and waxes. To manage odor and wetness, PG-free deodorants often rely on ingredients such as magnesium hydroxide, which neutralizes odor-causing bacteria, or absorbent powders like arrowroot powder, baking soda, or clay.
Consumers wishing to avoid propylene glycol should review the ingredient list for 1,2-propanediol or propylene glycol itself. Choosing products labeled “Propylene Glycol-Free” is the most direct approach. Finding a suitable alternative may require trial and error, as individual skin chemistry and sensitivity to substitute ingredients like baking soda can vary.