2026-01-23 Posted by TideChem view:77
Polyethylene glycol (PEG) and propylene glycol (PG) are common ingredients in many everyday products—from medicines and cosmetics to food and industrial formulations. Both are widely used as solvents, humectants, or stabilizers, but they are not the same material.
The key difference is structural: PEG is a polymer with a variable chain length, while PG is a small, single-molecule glycol. This difference in size and structure leads to noticeable differences in how they behave in real applications.
This guide explains how PEG and PG differ, how they’re used across industries, what to consider for safety, and how to choose the right one for a specific formulation.
|
Feature |
Polyethylene Glycol (PEG) |
Propylene Glycol (PG) |
|
Chemical Structure |
Polymer (n = 2–2000+); Mw 200–20,000 Da |
Small molecule; Mw 76.10 Da |
|
Physical State |
Liquid (<600 Da) to solid (>1000 Da) |
Clear, viscous liquid |
|
Solubility |
Water, ethanol, most organic solvents |
Water, ethanol, oils |
|
Moisturizing |
Moderate to high (increases with Mw) |
High (strong water-binding capacity) |
|
Biocompatibility |
Excellent; FDA-approved; low immunogenicity (except rare PEG hypersensitivity) |
Good; FDA-approved; mild irritation at high concentrations |
|
Stability |
pH 3–11; hydrolysis-resistant |
Stable under neutral/acidic conditions; degrades at high pH (>10) |
|
Main Functions |
Solvent, stabilizer, PEGylation agent, lubricant |
Solvent, humectant, plasticizer, preservative aid |
PEG
PEG is widely used to extend the circulation time of drugs, such as PEGylated proteins and antibody–drug conjugates (ADCs). It also serves as an excipient in oral and injectable formulations—PEG 400 is commonly used as a solvent for poorly soluble drugs. In addition, PEG lipids are key components of lipid nanoparticles for mRNA delivery.
PG
PG is commonly used as a solvent in liquid medicines and topical creams. It improves skin penetration in transdermal patches and is also used as a cryoprotectant to help preserve biological samples during freezing.
PEG
PEG appears in cleansers (e.g., PEG-40 castor oil), lotions (PEG 1500 as a thickener), and hair-care products. Lower-molecular-weight PEGs (200–600 Da) mainly act as humectants, while higher-molecular-weight PEGs affect texture and viscosity.
PG
PG is widely used in lotions and serums for strong hydration. It also works as a solvent in fragrances and helps disperse color evenly in hair dyes.
PEG
PEG is approved as a food additive (E1521), where it helps prevent caking and lubricates processing equipment. In industry, it is used as a plasticizer in coatings and as a modifier in chromatography.
PG
PG is approved as a food additive (E1520) for moisture retention. It is also used as a lower-toxicity antifreeze alternative and as a solvent in printing inks.
PEG
PEG is generally considered safe. However, in rare cases, PEGylated products may trigger allergic reactions (estimated at 0.01–0.1%). PEG should be avoided in individuals with known PEG sensitivity.
PG
PG may cause mild irritation to the eyes or broken skin. In topical products, concentrations are usually kept below 30%. High oral intake (above ~10 g/day) may cause gastrointestinal discomfort.
PEG
Choose molecular weight based on function:
PEG 200–400 for solvents
PEG 1000–4000 for thickening
PEG 5000+ for PEGylation
Avoid mixing very high–molecular-weight PEGs (>10,000 Da) directly with oils, as phase separation can occur.
PG
Avoid combining PG with strong bases (such as NaOH), which can cause degradation. Mixing PG with water or ethanol improves formulation stability.
|
Issue |
Cause |
Solution |
|
PEG aggregation |
High Mw or non-polar solvent |
Use lower-Mw PEG (≤600 Da), add co-solvent (ethanol), reduce concentration <20% |
|
PG irritation |
High concentration or sensitive skin |
Dilute <20%, or replace with PEG 400 |
|
Phase separation in PEG-oil blends |
Immiscibility |
Add surfactant (Tween 80) or switch to PG |
Not always. PEG is better suited for drug formulations and PEGylation, while PG performs better as a humectant and oil-compatible solvent. Always test before substitution.
Both typically have a shelf life of 2–5 years when stored in sealed containers at room temperature. Keep PEG away from moisture and PG away from strong bases.
Yes. Both are synthetic materials and do not contain animal-derived ingredients.
PG works well for very dry skin. PEG 400–600 provides lighter moisture for normal or combination skin. Many formulations use both for balanced hydration.
PEG and PG share some similar roles but are not interchangeable. Choosing the right glycol depends on molecular weight, solubility, hydration strength, and safety considerations. Understanding these differences helps achieve better performance in pharmaceutical, cosmetic, food, and industrial applications.