Regarding PEG-90 Glyceryl Isostearate, some cases of contact cheilitis have been reported (1).

Regarding safety in general, apart from cases of individual intolerance, a final report was issued in 2004 that considered this component safe for health (2).

References______________________________________________________________________

(1) Inui S, Azukizawa H, Katayama I. Recurrent contact cheilitis because of glyceryl isostearate, diisostearyl maleate, oleyl alcohol, and Lithol Rubine BCA in lipsticks. Contact Dermatitis. 2009 Apr;60(4):231-2. doi: 10.1111/j.1600-0536.2009.01513.x.

(2) Final report of the amended safety assessment of Glyceryl Laurate, Glyceryl Laurate SE, Glyceryl Laurate/Oleate, Glyceryl Adipate, Glyceryl Alginate, Glyceryl Arachidate, Glyceryl Arachidonate, Glyceryl Behenate, Glyceryl Caprate, Glyceryl Caprylate, Glyceryl Caprylate/Caprate, Glyceryl Citrate/Lactate/Linoleate/Oleate, Glyceryl Cocoate, Glyceryl Collagenate, Glyceryl Erucate, Glyceryl Hydrogenated Rosinate, Glyceryl Hydrogenated Soyate, Glyceryl Hydroxystearate, Glyceryl Isopalmitate, Glyceryl Isostearate, Glyceryl Isostearate/Myristate, Glyceryl Isostearates, Glyceryl Lanolate, Glyceryl Linoleate, Glyceryl Linolenate, Glyceryl Montanate, Glyceryl Myristate, Glyceryl Isotridecanoate/Stearate/Adipate, Glyceryl Oleate SE, Glyceryl Oleate/Elaidate, Glyceryl Palmitate, Glyceryl Palmitate/Stearate, Glyceryl Palmitoleate, Glyceryl Pentadecanoate, Glyceryl Polyacrylate, Glyceryl Rosinate, Glyceryl Sesquioleate, Glyceryl/Sorbitol Oleate/Hydroxystearate, Glyceryl Stearate/Acetate, Glyceryl Stearate/Maleate, Glyceryl Tallowate, Glyceryl Thiopropionate, and Glyceryl Undecylenate. Int J Toxicol. 2004;23 Suppl 2:55-94. doi: 10.1080/10915810490499064. 

PEG-90 Glyceryl Isostearate is a chemical compound, PEG, glycolic polyethylene ether of Glyceryl stearate, 

The name describes the structure of the molecule:

• PEG-90. PEG stands for polyethylene glycol. The number 90 indicates the average molecular weight of the polyethylene glycol portion of the molecule. Polyethylene glycol is a polymer based on ethylene oxide, and is often used as a solvent, thickener, or moisture-carrier in various products.
• Glyceryl refers to a group derived from glycerin, a simple polyol compound. Glycerol is a colorless, odorless and viscous liquid that has a sweet, non-toxic taste.
• Isostearate refers to the ester or saline form of isostearic acid, a type of fatty acid. Fatty acids are often used in skin care products for their moisturizing and emollient properties.

Description of raw materials used in production:

• Polyethylene Glycol (PEG) is a polymer derived from ethylene oxide. The number 90 in PEG-90 Glyceryl Isostearate refers to the average molecular weight of the polyethylene glycol component.
• Glyceryl Isostearate is an ester derived from glycerin and isostearic acid. It is commonly used in cosmetics as a conditioning and emollient agent.

The synthesised extraction process takes place in different steps:

• Extraction. The process begins with the extraction of fatty acids from natural sources such as vegetable oils or animal fats. Isostearic acid, a branched-chain fatty acid, is often used.
• Esterification. Isostearic acid is reacted with glycerine in a process known as esterification to form glyceryl isostearate. This reaction involves isostearic acid reacting with an alcohol (glycerine) to form an ester (glyceryl isostearate).
• Reaction with ethylene oxide. Glyceryl isostearate is then reacted with ethylene oxide in a process known as ethoxylation. This reaction attaches a chain of ethylene oxide units to the glyceryl isostearate molecule. The number 90 in PEG-90 Glyceryl Isostearate indicates that on average 90 ethylene oxide units are attached to each glyceryl isostearate molecule.

It is typically found in liquid form when used in cosmetic and personal care formulations. In its pure form, it is usually a clear or slightly yellowish liquid.

However, the appearance of the final product in which PEG-90 Glyceryl Isostearate is used can vary greatly depending on the other ingredients used in the formulation.

What it is used for and where

Cosmetics

Anionic surfactant chemical compound with an emulsifying function, i.e. a substance which tends to reduce the surface tension of a liquid in which it is dissolved and functions as an emollient and is used in cosmetics as a surfactant, i.e. of cleaning.

Surfactant - Cleansing agent. Cosmetic products used to cleanse the skin utilise the surface-active action that produces a lowering of the surface tension of the stratum corneum, facilitating the removal of dirt and impurities. 

Applications:

• Shampoo
• Detergents
• Lipsticks
• and more

Medical

Drug delivery

Safety

It is an ethoxylated product, but since 90 ethylene oxide units are not easily absorbed through the stratum corneum, it seems unlikely that skin penetration would cause damage.

Studies

Solid lipid nanoparticles (SLNs) represent an affordable, easily scalable, stable and biocompatible drug delivery system with a high drug to lipid ratio which also improves solubility of poorly soluble drugs. Solid lipid nanoparticles were developed by using glyceryl monostearate as the single lipid in the presence of surfactant Poloxamer 188 and evaluated the efficiency of SLNs to load the therapeutic cargo, curcumin. The results provide a strong rationale for further exploration of the newly developed CUR-SLN to be utilized as a potent chemotherapeutic agent in cancer therapy (1).

The product would be safe for human health (2).

This study has characterized an emulsion system stabilized by an amphiphilic random copolymer, methoxy polyethylene glycol-23 methacrylate/glyceryl diisostearate methacrylate copolymer (MPM-GDM). The combined results of the static surface tension and transmission electron microscopy with freeze-fracture technique (FF-TEM) suggested that this copolymer forms aggregates in aqueous solutions. The membrane emulsification method produced an oil-in-water (O/W) emulsion in the mixture of squalane, water, and MPM-GDM, where the squalane concentration was set at 10 - 60 wt% and the MPM-GDM concentration was either 1 or 5 wt%. The prepared emulsion was stable against coalescence due to the formation of an adsorption layer of MPM-GDM. Based on the FF-TEM results, it is confirmed that a relatively large island-like structure is formed on the emulsion droplet surface. Furthermore, MPM-GDM can act as a thickening agent of the continuous liquid phase, which enhances the stability against creaming. The cooperative two effects improve the stability of the emulsion system without adding co-stabilizer such as low molecularweight surfactants (3).

The most relevant studies on this chemical compound have been selected with a summary of their contents:

Glyceryl Isostearate studies

General Features:

• Form Crystals; color< 6 on Gardner scale 
• Odor Faint
• Specific gravity at 20◦C 0.930 to 0.970 
• Refractive index at 20◦C 1.455 to 1.475 
• Viscosity at 20◦C 0.7 to 1.2 Pa 
• Hydroxyl value 180–280 mg KOH/g 
• Iodine value <15 g/100 g (based on I2) 
• Saponification value 150–170 mg 
•  Acid value <4 mg KOH/g

Synonyms:

(1)-2,3-Dihydroxypropyl stearate.alpha.-Monostearin1379-EP2270002A11379-EP2270006A11379-EP2270011A11379-EP2277861A11379-EP2277865A11379-EP2281823A21379-EP2289892A11-Glyceryl stearate1-Monostearoylglycerol1-octadecanoylglycerol1-octadecanoyl-rac-glycerol1-O-stearoylglycerol2,3-Dihydroxypropyl 16-methylheptadecanoate2,3-Dihydroxypropyl isooctadecanoate2,3-dihydroxypropyl octadecanoate2,3-Dihydroxypropyl stearate342394-34-737349-34-13-Stearoyloxy-1,2-propanediol8029-22-983138-62-985666-92-8AB1009437Abracol S.L.G.AK175522Aldo 33Aldo 75Aldo MSDAldo MSLGalpha-MonostearinAN-22932Arlacel 165CAS-11099-07-3CAS-123-94-4CC-06953DL-|A-StearinDSSTox_CID_9160DSSTox_GSID_29160DSSTox_RID_78691Eastman 600EINECS 204-664-4EINECS 245-121-1Emerest 2407FEMA No. 2527FT-0626740FT-0626748G0085Glycerin 1-monostearateGlycerin 1-stearateGlycerol .alpha.-monostearateGlycerol 1-monostearateglycerol 1-octadecanoateGlycerol 1-stearateGlycerol alpha-monostearateGlycerol Mono StearateGlycerol monoisostearateGlycerol stearate, pureGlyceryl 1-monostearateGlyceryl 1-octadecanoateGlyceryl monoisostearateGlyceryl monostearateGlyceryl monostearate [JAN:NF]Glyceryl Stearate SEGlyceryl-1-monostearateIsooctadecanoic acid, monoester with 1,2,3-propanetriolIsooctadecanoic acid,ester with 1,2,3-propanetriolIsooctadecanoicacid,esterwith1,2,3-propanetriolLS-164168MONOSTEARIN (L)Monostearin (Related)NCGC00164529-01NSC 3875NSC3875Octadecanoic acid, 2,3-dihydroxypropyl esterP566Polyglyceryl-3 stearateQ-201168rac-Glycerol 1-stearaterac-glyceryl monostearaterac-octadecanoylglycerolS-7950Sandin EUSC-19844SC-79530ST51037333Stearic acid 1-monoglycerideStearic acid alpha-monoglycerideStearin, 1-mono-Stearin, mono-Tegin (Related)Tegin 515Tegin 55GTEGIN 90Triglyceryl monostearateW-110285

References_____________________________________________________________________

(1) Bhatt H, Rompicharla SVK, Komanduri N, Aashma S, Paradkar S, Ghosh B, Biswas S. Development of Curcumin-Loaded Solid Lipid Nanoparticles Utilizing Glyceryl Monostearate as Single Lipid Using QbD Approach: Characterization and Evaluation of Anticancer Activity Against Human Breast Cancer Cell Line. Curr Drug Deliv. 2018;15(9):1271-1283. doi: 10.2174/1567201815666180503120113.

(2) Amended final report on the safety assessment of glyceryl dilaurate, glyceryl diarachidate, glyceryl dibehenate, glyceryl dierucate, glyceryl dihydroxystearate, glyceryl diisopalmitate, glyceryl diisostearate, glyceryl dilinoleate, glyceryl dimyristate, glyceryl dioleate, glyceryl diricinoleate, glyceryl dipalmitate, glyceryl dipalmitoleate, glyceryl distearate, glyceryl palmitate lactate, glyceryl stearate citrate, glyceryl stearate lactate, and glyceryl stearate succinate. Int J Toxicol. 2007;26 Suppl 3:1-30. doi: 10.1080/10915810701663143. 

(3) Kaji M, Fujiwara S, Sakai K, Sakai H. Characterization of O/W Emulsions Prepared by PEG-Diisostearate Amphiphilic Random Copolymer. J Oleo Sci. 2017 Oct 1;66(10):1121-1128. doi: 10.5650/jos.ess17044. 

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And a premise on PEG.

Since the PEG (1) family is numerous and is found in many cosmetic, cleaning and medicinal products and others, we need a cognitive premise on the subject that is rather complex from the point of view of safety because these products not only come into contact with the skin but, as in the case of medicine, they are also ingested.

PEG or polyethylene glycols polymerise the condensed ethylene oxide and water and are called polyethylene glycols, but in reality, they are complex chemical components, polymers bound together. For example,  plastic is polyethylene and has a hard consistency, while  polyethylene aggregated to the glycol forms a liquid.

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

Here below are some studies in Medicine that refer to the use of PEG Polyethylene glycol in various fields.

Intestine

Polyethylene glycol with or without electrolytes is effective for the treatment of functional constipation, both in adults and in paediatric patients, with great safety and tolerability. These preparations are the most effective osmotic laxatives (more than lactulose) and are the first-line treatment for functional constipation in the short- and long-term. They are as effective as enemas in faecalomas, avoid the need for hospitalisation and are well tolerated by patients (especially when given without electrolytes) (2).

In the preparation  for colonoscopy,  polyethylene glycol tablets confirmed efficacy, acceptability, tolerance and safety similar to those of sodium phosphate (3).

For peripheral nerve repair (4).

Eyes

Dry eye syndrome is a disorder that affects 5-34% of the world's adult population with reduced quality of life. Artificial or lubricating tears are the most used therapy for treating this condition due to their low side effects profile, which attempt to modify the properties of the tear film. Polyethylene glycol has demonstrated clinical efficacy in the treatment of this condition (5).

Brain

Polyethylene glycol facilitates the neuroprotective effects of magnesium in head injuries (6).

Tumors

For transarterial chemoembolization, Polyethylene glycol is effective and safe for the treatment of liver cancer, as indicated by good tolerability, quality of life and high tumour response (7). 

Cosmetics

Many types of PEG are hydrophilic and are used as creams, topical dermatological preparations and in cosmetic products such as surfactants, emulsifiers, detergents, humectants and skin conditioners.

Safety varies from type to type given the structural complexity (8).

References___________________________________________________________________

(1) Fruijtier-Pölloth C. Safety assessment on polyethylene glycols (PEGs) and their derivatives as used in cosmetic products. Toxicology. 2005 Oct 15;214(1-2):1-38. doi: 10.1016/j.tox.2005.06.001.

(2) Mínguez M, López Higueras A, Júdez J. Use of polyethylene glycol in functional constipation and fecal impaction. Rev Esp Enferm Dig. 2016 Dec;108(12):790-806. doi: 10.17235/reed.2016.4571/2016.

Santos-Jasso KA, Arredondo-García JL, Maza-Vallejos J, Lezama-Del Valle P. Effectiveness of senna vs polyethylene glycol as laxative therapy in children with constipation related to anorectal malformation. J Pediatr Surg. 2017 Jan;52(1):84-88. doi: 10.1016/j.jpedsurg.2016.10.021.

(3) Chaussade S, Schmöcker C, Toulemonde P, Muñoz-Navas M, O'Mahony V, Henri F. Phosphate tablets or polyethylene glycol for preparation to colonoscopy? A multicentre non-inferiority randomized controlled trial. Surg Endosc. 2017 May;31(5):2166-2173. doi: 10.1007/s00464-016-5214-1.
Tsunoda T, Sogo T, Iwasawa K, Umetsu S, Oikawa-Kawamoto M, Inui A, Fujisawa T. Feasibility and safety of bowel cleansing using low-volume polyethylene glycol with ascorbic acid before pediatric colonoscopy: A pilot study. Dig Endosc. 2017 Mar;29(2):160-167. doi: 10.1111/den.12756.

(4) Hoffman AN, Bamba R, Pollins AC, Thayer WP. Analysis of polyethylene glycol (PEG) fusion in cultured neuroblastoma cells via flow cytometry: Techniques & optimization. J Clin Neurosci. 2017 Feb;36:125-128. doi: 10.1016/j.jocn.2016.10.032.

(5) Pérez-Balbuena AL, Ochoa-Tabares JC, Belalcazar-Rey S, Urzúa-Salinas C, Saucedo-Rodríguez LR, Velasco-Ramos R, Suárez-Sánchez RG, Rodríguez-Carrizalez AD, Oregón-Miranda AA. Efficacy of a fixed combination of 0.09 % xanthan gum/0.1 % chondroitin sulfate preservative free vs polyethylene glycol/propylene glycol in subjects with dry eye disease: a multicenter randomized controlled trial. BMC Ophthalmol. 2016 Sep 20;16(1):164. doi: 10.1186/s12886-016-0343-9.

Labetoulle M, Messmer EM, Pisella PJ, Ogundele A, Baudouin C. Safety and efficacy of a hydroxypropyl guar/polyethylene glycol/propylene glycol-based lubricant eye-drop in patients with dry eye. Br J Ophthalmol. 2017 Apr;101(4):487-492. doi: 10.1136/bjophthalmol-2016-308608.

(6) Busingye DS, Turner RJ, Vink R. Combined Magnesium/Polyethylene Glycol Facilitates the Neuroprotective Effects of Magnesium in Traumatic Brain Injury at a Reduced Magnesium Dose. CNS Neurosci Ther. 2016 Oct;22(10):854-9. doi: 10.1111/cns.12591.

(7) Aliberti C, Carandina R, Sarti D, Mulazzani L, Catalano V, Felicioli A, Coschiera P, Fiorentini G. Hepatic Arterial Infusion of Polyethylene Glycol Drug-eluting Beads for Primary and Metastatic Liver Cancer Therapy. Anticancer Res. 2016 Jul;36(7):3515-21.

(8) Jang HJ, Shin CY, Kim KB. Safety Evaluation of Polyethylene Glycol (PEG) Compounds for Cosmetic Use. Toxicol Res. 2015 Jun;31(2):105-36. doi: 10.5487/TR.2015.31.2.105.