What it is
Polypropylene Glycol (PPG) is a synthetic polyether produced by the ring-opening polymerization of propylene oxide. It is a clear, colorless to light yellow viscous liquid available in a wide range of molecular weights, typically designated by a number suffix (e.g., PPG-4 through PPG-69). Lower-molecular-weight PPGs are water-miscible, while higher-molecular-weight variants are less soluble in water. In cosmetic formulations, PPG primarily functions as a skin conditioning agent and solvent, helping to dissolve or disperse other ingredients and contributing to smooth product application. It is less toxic than comparable polyethylene glycols (PEGs) and offers good biodegradability. PPG may also act as a humectant in some formulations, helping skin retain moisture. It is used across a range of leave-on and rinse-off products.
Safety & warnings
The CIR Expert Panel (2012) concluded that PPGs with a repeat unit count of 3 or more are safe as used in cosmetic formulations when formulated to be non-irritating. Clinical studies found no significant dermal sensitization at typical use concentrations. PPG may contain trace residual propylene oxide (manufacturing impurity), which should be controlled to ≤10 ppm. Acute oral studies in animals showed very low systemic toxicity. PPG is not considered genotoxic, carcinogenic, or a reproductive/developmental toxicant. Individuals with very sensitive skin may experience mild irritation in some formulations. Higher concentrations (up to 22% have been reported in some products) are used without adverse effects in most consumers.
Origin & sourcing
Polypropylene Glycol is produced synthetically via ring-opening polymerization of propylene oxide, using an alcohol (such as ethylene glycol or water) as an initiator and a base catalyst, typically potassium hydroxide. The polymer structure is linear when a bifunctional initiator is used and branched when a multifunctional initiator such as glycerine or sorbitol is used. Propylene oxide itself is derived from petroleum-based feedstocks. The process is well-established industrially; between 60 and 70% of propylene oxide is converted to polyether polyols through this alkoxylation route.
History
Polypropylene Glycol was developed as part of broader polyether polyol chemistry that expanded significantly in the mid-20th century alongside the polyurethane industry. Its use in cosmetics was reviewed by the Cosmetic Ingredient Review (CIR) Expert Panel in 2012, which concluded that PPG grades of 3 and above are safe for use in cosmetic formulations when formulated to be non-irritating. The EU CosIng database lists PPG as a permitted cosmetic ingredient. CAS number 25322-69-4 is assigned to the polymer class.
Questions everyone asks
What does Polypropylene Glycol do in sunscreen and skincare products?
It primarily acts as a skin conditioning agent and solvent. It helps other ingredients dissolve or disperse evenly, contributes to smooth application, and can help skin retain moisture. It does not provide UV protection itself.
Is Polypropylene Glycol safe for sensitive skin?
The CIR Expert Panel concluded it is safe when formulated to be non-irritating. Most consumers tolerate it well. People with very sensitive skin should patch-test products containing higher concentrations, as some may experience mild irritation.
How does Polypropylene Glycol differ from Propylene Glycol?
Polypropylene Glycol is a polymer (long chain) of propylene glycol monomers. This makes it larger, more viscous, and less water-soluble at higher molecular weights than simple propylene glycol, while sharing similar conditioning and solvent properties.
Is Polypropylene Glycol natural or synthetic?
It is a synthetic ingredient, produced by polymerizing propylene oxide derived from petroleum feedstocks. It is not found in nature but has a well-established safety profile in cosmetic use.