Methylene glycol or hydrated formaldehyde is formed upon dissolution of formaldehyde in water and exists in equilibrium with formaldehyde in aqueous solutions.
While restrictions for the use of formaldehyde in cosmetic products exist, methylene glycol is not explicitly included in these entries, so the Scientific Committee on Consumer Safety (SCCS) was asked to announce its opinion.
To be or not to be…
As part of its investigation, SCCS were asked primarily to comment, based on the science, on whether methylene glycol should be considered as a formaldehyde equivalent.
“Although formaldehyde and methylene glycol are different molecules from a scientific chemical point of view, there is a close interrelationship of formaldehyde and methylene glycol in aqueous solution and a rapid mutual conversion in a dynamic equilibrium,” says the EC statement.
Therefore, SCCS states it is justified to consider the aqueous mixture of gaseous formaldehyde and methylene glycol as “free formaldehyde” and the quantities as “formaldehyde equivalents” in aqueous solutions.
Having established methylene glycol as an equivalent, SCCS then stated that its use in hair straightening products at a concentration of 0.2 per cent, the amount of gaseous formaldehyde released may exceed 0.1 mg/m³ (0.08 ppm), which is the WHO indoor air quality guideline for short term exposure.
Methylene glycol produces gaseous formaldehyde under the intended conditions of use in hair straightening products due to the application of heat by straightening irons and/or blow drying.
“The use of methylene glycol/formaldehyde at 0.2 per cent formaldehyde equivalent is not considered safe in hair straighteners,” said the statement.
Manufacturers of hair straightening products have claimed being compliant with the cosmetics legislation, arguing that methylene glycol is chemically different from formaldehyde and as free formaldehyde is only present in trace amounts in the product.
Moreover, it was argued that the official EU analytical method for determination of free formaldehyde would produce artificially high results, as during the analysis methylene glycol is converted to formaldehyde, and thus the measured values do not reflect the formaldehyde levels in the cosmetic product.
However, according to the Member State assessments, formaldehyde vapours are generated during normal use of such hair straightening products, as this procedure involves treatment with a hot straightening iron at temperatures of 230 degrees.
“It is assumed that the application of heat converts methylene glycol to formaldehyde, which then can act as a fixative in the hair,” says the EC.