PEG-45: properties, uses, pros, cons, safety

PEG-45M is a high-molecular-weight polyethylene glycol, described as poly(oxy-1,2-ethanediyl) with .alpha.-hydro and .omega.-hydroxy end groups, i.e., a PEG diol polymer. The “45,000 mol EO average molar ratio” parameter indicates a very long chain, typically associated with more thickening and film-forming behavior than low-MW PEGs.

In cosmetic formulations it is mainly used as a humectant, increasing water retention in the aqueous phase and helping reduce evaporative water loss. It can also support rheology by improving viscosity, slip, and texture stability, especially in gels and lotions. Its presence can provide a longer-lasting hydration feel by forming a continuous hydrophilic film on the surface. It is used in leave-on and rinse-off products (lotions, light creams, gels, cleansers) as a structuring aid and carrier.

Performance depends on concentration, compatibility with surfactants and salts, and it can influence clarity and physical stability of the system. Selection of use level and polymer grade is driven by sensory/performance targets and finished-formula tolerability. 

The name defines the structure of the molecule

• "PEG" indicates that the molecule is a Polyethylene Glycol, a synthetic polymer used in many industrial and pharmaceutical applications.
• "45M" indicates the average molecular weight (45,000 mol EO average molar ratio).

Description of the raw materials used in production and their functions:

• Ethylene oxide (EO) is the primary raw material for PEG production.
• Catalysts. Used to accelerate the polymerization reaction.

Step-by-step industrial synthesis:

Ethylene oxide is fed into a reactor under controlled conditions.

• In the presence of a catalyst, the ethylene oxide polymerizes, forming PEG chains.
• Once the desired molecular weight is achieved (in this case, corresponding to PEG-45M), the reaction is halted.
• The PEG is then purified to remove any impurities or unreacted reagents.
• Finally, the PEG-45M is dried and conditioned to meet the desired specifications.

It appears as a white powder or as a clear viscous liquid.

What it is for and where

Cosmetics

Humectant. Hygroscopic compound used to minimise water loss in the skin and to prevent it from drying out by facilitating faster and greater absorption of water into the stratum corneum of the epidermis.  The epidermis is the most superficial of the three layers that make up human skin (epidermis, dermis and hypodermis) and is the layer that maintains hydration in all three layers. In turn, the epidermis is composed of five layers: horny, the most superficial, granular, spinous, shiny, and basal. Humectants have the ability to retain the water they attract from the air in the stratum corneum and have the function of moisturising the skin. They are best used before emollients, which are oil-based.

CAS   25322-68-3

Commercial Applications

Cosmetics and Skin Care. PEG-45M is commonly used in cosmetic products as an emollient and humectant. It aids in moisturizing the skin and improving the distribution of other ingredients within a formulation.

Hair Care Products. It can be found in shampoos, conditioners, and hair treatments where it acts as a conditioning agent, helping to make hair soft and manageable.

Safety

Pay particular attention to ethoxylated products, which are chemical compounds treated with ethylene oxide, as potentially harmful residues may remain during the processing process. It is essential to choose high quality ethoxylated products rather than relying solely on price. The production process of polyoxyethylene ester–based surfactants and emulsifiers consists of the ethoxylation of fatty acids, carried out through non-catalyzed or alkali-catalyzed reactions. Ethoxylated surfactants may contain 1,4-dioxane, a carcinogenic substance that is a by-product of the ethoxylation process and should be removed during the purification of the finished products. At the end of the production cycle, traces of reagents may remain in the finished product, including stearic acid, ethylene oxide, and the catalysts used. (Cosmetic Ingredient Review Safety Assessment of PEG Diesters as Used in Cosmetics  Dicember 22, 2014)