Science
Mechanism of Action
In aqueous solutions, methylene glycol maintains a rapid and reversible equilibrium with formaldehyde. Its primary mechanism in cosmetic formulations is to function as an antimicrobial and preservative through the controlled release of formaldehyde, which inhibits microbial growth. In specific applications like nail hardeners, it can bond with keratin to strengthen the nail structure.
Research
Clinical Evidence
Low confidenceN/A
Transparency
Dusting Analysis
The Formula
Formulation
Stability
Methylene glycol is an aqueous solution of formaldehyde, existing in a rapid, reversible equilibrium. This equilibrium can easily shift, leading to increased gaseous formaldehyde release under conditions such as heating or drying. This dehydration of methylene glycol to formaldehyde is particularly observed within the pH range of 6.0-7.8. Formaldehyde's high reactivity, while beneficial for preservation, also significantly contributes to its irritant activity.
Safety
Safety Profile
The CIR Expert Panel considers methylene glycol (as formaldehyde equivalent) safe in cosmetic products at 0.2% or less, but new clinical studies indicate it can be a skin irritant and sensitizer at higher levels. It is deemed unsafe in hair straightening products under current use practices. The SCCS also classifies methylene glycol as a formaldehyde equivalent, deeming its use in hair straightening products at 0.2% formaldehyde equivalent unsafe due to potential gaseous formaldehyde release exceeding WHO guidelines. In the EU, both formaldehyde and methylene glycol have been prohibited from use in cosmetics since January 1, 2016, owing to their classification as a Category 1B Carcinogen, Mutagen, or Reproductive Toxicant (CMR). Furthermore, California Assembly Bill No. 496 will ban methylene glycol from cosmetic products sold or manufactured in California starting January 1, 2025, due to its potential to release formaldehyde. The FDA communicates potential risks of products containing formaldehyde or related ingredients in hair smoothing products, while recognizing formaldehyde as safe in topical cosmetic products below 0.074%.
Your Skin
Skin Compatibility
Our Assessment
Verdict
Due to its classification as a CMR substance in the EU, its potential to release formaldehyde, and its high risk for skin irritation and sensitization, methylene glycol is unequivocally advised against in skincare formulations.
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