Polyethylene glycol is not one single substance. It is a family of water-soluble polymers with different molecular weights. peg 400 is a low-molecular-weight, liquid grade with an average molecular weight near 400 daltons. It usually appears as a clear, nearly colorless liquid. Its mildly viscous texture resembles light syrup. The material mixes readily with water and many polar solvents, which explains its wide commercial value.
The details matter.
The United States Pharmacopeia–National Formulary lists polyethylene glycol as a pharmaceutical-grade excipient with defined quality requirements. The FDA Inactive Ingredient Database also records polyethylene glycol in approved drug products, although permitted use depends on the product and route of administration. In cosmetics, PEG 400 commonly functions as a solvent, humectant, or viscosity modifier. In manufacturing, it supports formulations that require predictable blending and moisture control. It is not automatically interchangeable with higher-molecular-weight PEG grades.
Industry data shows continuing demand. Grand View Research reports that the global polyethylene glycol market was valued at several billion U.S. dollars in 2023, with pharmaceutical and personal-care applications among its key growth areas. MarketsandMarkets similarly identifies healthcare, cosmetics, and industrial formulations as major demand segments. These reports use different market definitions, so their figures should not be treated as identical. That limitation is important.
This guide explains what PEG 400 is, how manufacturers evaluate it, and where it is used. It also considers purity, storage, compatibility, and regulatory expectations. A simple description can be useful. It can also hide important differences between grades, suppliers, and applications.
PEG 400 is a clear, water-miscible liquid made from polyethylene glycol molecules. The number 400 shows its approximate average molecular weight, not an exact measurement. Manufacturers commonly produce it through controlled ethoxylation. During this process, ethylene oxide reacts with water or another suitable glycol. Heat, pressure, catalysts, and reaction time must be carefully managed. Ethylene oxide is hazardous during production, so professional facilities use sealed systems and strict controls.
After the reaction, the material undergoes purification. This step can remove unreacted ingredients, moisture, salts, and unwanted molecular fractions. Manufacturers then test its appearance, viscosity, acidity, water content, and molecular-weight distribution. These checks help determine whether the material fits pharmaceutical, cosmetic, food-processing, or industrial specifications. However, PEG 400 is not always identical between suppliers. Small differences can affect texture, flow, and performance.
Tips: Check the product’s certificate of analysis before choosing it. Match the grade to its intended application. Store it in a tightly closed container, away from excessive heat and contamination. Do not assume that every clear liquid is suitable for medical or personal use. That shortcut can cause problems.
| Category | Attribute | Information |
|---|---|---|
| Basic Identity | Full Name | Polyethylene glycol 400, commonly abbreviated as PEG 400. |
| Basic Identity | Chemical Classification | A water-soluble polyether polymer made from repeating ethylene oxide units. |
| Basic Identity | CAS Registry Number | 25322-68-3. |
| Molecular Information | General Structural Formula | HO–(CH2CH2O)n–H. |
| Molecular Information | Average Molecular Weight | Approximately 400 g/mol; the number indicates an average molecular weight rather than a single molecular mass. |
| Physical Properties | Appearance | Typically a clear, colorless or nearly colorless, viscous liquid at room temperature. |
| Physical Properties | Water Solubility | Miscible or highly soluble in water. PEG 400 is also compatible with many polar solvents. |
| Physical Properties | Moisture Behavior | Hygroscopic, meaning it can absorb moisture from the surrounding air. |
| Physical Properties | Density | Generally about 1.12–1.13 g/mL near 20°C, depending on grade and measurement conditions. |
| How It Is Made | Starting Materials | Usually produced from ethylene glycol or another low-molecular-weight glycol and ethylene oxide. |
| How It Is Made | Main Manufacturing Reaction | Ethylene oxide is added to the glycol starter through controlled ethoxylation, forming chains of repeating oxyethylene units. |
| How It Is Made | Molecular-Weight Control | The average molecular weight is controlled mainly by the ratio of ethylene oxide to the starting glycol and by reaction conditions. |
| How It Is Made | Finishing Steps | The reaction mixture is commonly neutralized or treated as needed, then purified, filtered, and tested to meet the required specification. |
| Pharmaceutical Uses | Excipient and Solvent | Used as a solvent, vehicle, plasticizer, humectant, and viscosity-modifying ingredient in selected pharmaceutical formulations. |
| Pharmaceutical Uses | Oral Laxative Function | At appropriate medically formulated doses, PEG 400 can act as an osmotic laxative by retaining water in the intestinal contents. |
| Cosmetic and Personal Care Uses | Formulation Role | Used as a solvent, moisture-retaining ingredient, texture modifier, and carrier in creams, lotions, gels, and other water-compatible formulations. |
| Industrial Uses | Processing Aid | Used in coatings, inks, adhesives, lubricants, polymer processing, and other applications where water compatibility and low volatility are useful. |
| Material Compatibility | Blending Behavior | Can blend with water and many polar materials, but compatibility with hydrophobic materials depends on the specific formulation and additives. |
| Handling and Storage | Recommended Conditions | Store in a tightly closed container in a cool, dry, well-ventilated area and protect it from excessive moisture and contamination. |
| Safety Considerations | General Precaution | Although PEG 400 generally has low acute toxicity, the appropriate grade, concentration, and intended-use requirements should always be followed. |
| Important Distinction | PEG 400 Is Not a Single Pure Molecule | It is a distribution of polyethylene glycol molecules with different chain lengths centered around an average molecular weight of approximately 400. |
Values may vary by specification, manufacturing method, temperature, and intended application. Always consult the relevant technical specification and safety documentation before use.
