Isopropyl Methylphenol — INCI reference

What it is

Isopropyl Methylphenol (IPMP), chemically identified as 4-isopropyl-3-methylphenol (CAS 3228-02-2), is a white crystalline solid with molecular formula C₁₀H₁₄O and molecular weight 150.22 g/mol. It is a structural isomer of thymol, the natural antimicrobial found in thyme oil. IPMP is insoluble in water but soluble in ethanol, methanol, isopropanol, and acetone. It functions as a broad-spectrum preservative and biocide in cosmetic formulations, inhibiting the growth of bacteria, yeasts, molds, and some viruses at low concentrations (up to 0.1% in the EU). Its low odor profile and mild astringency make it suitable for skin care creams, shampoos, hair dyes, toothpastes, mouthwashes, and compact powders. Effectiveness may be reduced in the presence of certain surfactants; adding chelating agents such as EDTA can restore activity. The EU Cosmetics Regulation permits its use as a preservative at up to 0.1%.

Safety & warnings

IPMP has a reported skin sensitization rate of approximately 2%, which is relatively low for a preservative. It is generally considered mild with no GHS hazard classification under standard cosmetic use. Animal studies noted some neurotoxic effects at high doses, leading to heavier restrictions in certain jurisdictions. The EU limits its use to 0.1% as a preservative. Users with phenol or thymol hypersensitivity may wish to exercise caution. It is stable under typical storage conditions (air, light, temperature, humidity) and does not degrade into known toxic byproducts under normal use.

Origin & sourcing

Isopropyl Methylphenol is a fully synthetic compound produced by chemical synthesis, typically via alkylation of m-cresol (3-methylphenol) with propylene or isopropanol under acidic catalysis. It does not occur naturally at commercially significant levels, though it is a structural isomer of thymol, which is found naturally in the essential oil of thyme (Thymus vulgaris). Industrial production methods were established in the 1950s.

History

IPMP was first synthesized and characterized in the early 1950s, with industrial manufacturing processes developed around 1953. It was studied as a synthetic alternative to natural thymol, sharing the same molecular formula but offering a more reproducible and cost-effective supply. The EU included o-Cymen-5-ol in Annex V (permitted preservatives) of the Cosmetics Regulation (EC) No 1223/2009 at a maximum concentration of 0.1%. The CIR Expert Panel assessed o-Cymen-5-ol and concluded it was safe in cosmetics at concentrations up to 0.5%.

Questions everyone asks

What is Isopropyl Methylphenol used for in skin care products?

It is used primarily as a preservative and antimicrobial agent to protect cosmetic products from bacterial and fungal contamination. It appears in creams, shampoos, hair dyes, toothpastes, and compact powders.

Is Isopropyl Methylphenol the same as thymol?

No, but they are structural isomers — both have the molecular formula C₁₀H₁₄O. Isopropyl Methylphenol (4-isopropyl-3-methylphenol) is a synthetic compound, while thymol (2-isopropyl-5-methylphenol) is naturally derived from thyme oil. They share similar antimicrobial properties.

At what concentration is Isopropyl Methylphenol used in cosmetics?

The EU Cosmetics Regulation permits it as a preservative at a maximum concentration of 0.1%. The CIR Expert Panel concluded it is safe at concentrations up to 0.5%.

Is Isopropyl Methylphenol safe for sensitive skin?

It has a relatively low sensitization rate (~2%) compared to many other preservatives. However, individuals sensitive to phenolic compounds or thymol should review formulations carefully.

Sources & references

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