Glycols have been used in cosmetics and personal care products to impart beneficial properties such as humectancy, solvency, moisturization and emulsification. One such ingredient is 1,3-propanediol (PDO), which is manufactured either by a chemical process using petroleum feedstock or by a fermentation (bio-based) process using corn sugar. Since PDO became commercially available only recently, it does not yet have a widespread history of use for properties such as humectancy, moisturization or emulsification. However, a substance structurally similar to PDO, propylene glycol (PG) (see Figure 1), does have widespread use and distribution in personal care products—but it also has a history of some dermal irritation and to a lesser extent, sensitization.1, 2
Obviously, besides the efficacy properties of a raw material, another critical property is the lack of or low potential for dermal irritation and sensitization of skin. Therefore, an evaluation of the potential for new ingredients to cause adverse skin reactions is essential.3 Information from previous animal studies following exposure to chemically-produced PDO suggests a low potential for human skin reactions. This historical information includes a study in rabbits (Draize method), showing neat PDO is mildly irritating;4 and a study in guinea pigs (Landsteiner/Draize method), showing no dermal irritation or sensitization.5
Lab Practical: Using PDO
- When replacing another glycol with PDO, substitute it 1:1 in the formulation.
- If cloudiness or solubility issues arise, adjust the order of addition and mix PDO into the aqueous phase and/or increase the blending temperature.
- When formulating solid deodorants, increase the blending temperature.
- 60% maximum PDO is recommended for solid deodorant sticks with sodium stearate; if shrinkage occurs, a solubilizing agent is recommended.