PEG-4 (Poly(oxy-1,2-ethanediyl), .alpha.-hydro-.omega.-hydroxy- (4 mol EO average molar ratio)) is a synthetic polymer used primarily as a humectant, emulsifier, and solvent in cosmetic formulations. It is valued for its ability to retain moisture, enhance product texture, and improve the overall feel of formulations on the skin and hair.

Chemical Composition and Structure

The chemical composition of PEG-4 includes:

• Polyethylene Glycol: A polymer made from repeated units of ethylene oxide, with an average molecular weight that provides specific properties.
• Hydroxyl Groups: Present in the structure, contributing to its hydrophilic nature and moisture-retaining capabilities.

Structurally, PEG-4 consists of shorter chains of ethylene glycol compared to higher molecular weight PEGs, allowing for a more fluid consistency that aids in formulation stability and efficacy.

Physical Properties

• Appearance: Typically a clear to slightly yellow viscous liquid.
• Solubility: Soluble in water and various organic solvents, making it versatile for different formulations.
• pH: Generally neutral to slightly acidic, around 6-7.
• Odor: Mild, characteristic of polyethylene glycol compounds.
• Stability: Stable under normal storage conditions; should be protected from extreme temperatures.

Production Process

• Synthesis: PEG-4 is produced through the polymerization of ethylene oxide under controlled conditions to achieve the desired molecular weight.
• Purification: The resulting polymer is purified to remove unreacted materials and impurities.
• Formulation: The purified PEG-4 is incorporated into cosmetic products, often combined with other ingredients to enhance performance and stability.

Applications

• Medical: Limited use in specific formulations requiring moisture retention.
• Cosmetics: Commonly used in moisturizers, creams, lotions, and hair care products for its hydrating and texturizing effects.

CAS   25322-68-3

INCI Functions:

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.

Solvent. It is the substance for dissolving or dispersing surfactants, oils, dyes, flavourings, bactericidal preservatives in solution.In fact, it dissolves other components present in a cosmetic formulation. Solvents are generally liquid (aqueous and non-aqueous).

• Industrial Uses: Occasionally utilized in formulations requiring emulsification and moisture retention.

Environmental and Safety Considerations

Responsible sourcing and production practices are essential to ensure that the ingredient is free from harmful contaminants and produced sustainably. 

Cosmetic Safety

PEG (Polyethylene glycol) polymerize condensed ethylene oxide and water and are referred to as polyethylene glycols, but they are actually complex chemical components, polymers bonded together. For example, plastic is polyethylene and has a hard consistency, while polyethylene aggregated with glycol forms a liquid. PEGylation is produced not only as heterification but also as transesterification, which is the transformation of an alcohol by an ester. 

The number that appears after the abbreviation PEG represents the molecular weight, and the higher this number is, the less it penetrates the skin.

The term 'eth' refers to the ethoxylation reaction with ethylene oxide after which residues of ethylene oxide and 1,4-dioxane, chemical compounds considered carcinogenic, may remain. The degree of safety therefore depends on the degree of purity of the compound obtained. No manufacturer appears to provide this information on the label, at least as of the date of this review.

Kim MC, Park SY, Kwon SY, Kim YK, Kim YI, Seo YS, Cho SM, Shin EC, Mok JH, Lee YB. Application of Static Headspace GC-MS Method for Selective 1,4-Dioxane Detection in Food Additives. Foods. 2023 Sep 2;12(17):3299. doi: 10.3390/foods12173299. 

Abstract. "Efficient detection methods must be developed for 1,4-dioxane due to its suspected status as a human carcinogen, which is highly mobile in food and environmental resources. In this regard, this experiment has been conducted to develop reliable and selective detection and measurement methods by using static headspace (SH) isolation, followed by gas chromatography-mass spectrometry (GC-MS). A new method was developed for determining the spiked 1,4-dioxane contents in a polyethylene glycol 600 (PEG 600). The optimal condition for SH-GC-MS was discussed. The representative ions of 1,4-dioxane and 1,4-dioxane-d8 in the SIM mode of MS are 88 and 96, respectively, and the peaks of the SIM mode were separated and confirmed. The linear range for the method covers 0.25 to 100 mg/L with a coefficient of determination (R2) ≥ 0.999. The method applicability was demonstrated by spike recovery across a variety of food additives (i.e., chlorine bitartrate, choline chloride, polysorbate 20 and 60, and PEG 1000). All spike recovery from the tested samples was in the range of 89.50-102.68% with a precision of 0.44-11.22%. These findings suggest a new analytical method for food safety inspection, and could be applicable for ensuring the safety of foods and environmental and public health on a broad scale."