Is Sodium Hydroxymethylglycinate a Natural Preservative?

We've recently saw a dog shampoo that had "natural preservative" listed under ingredients.

This same product claimed this preservative was "gentle and based on the natural amino acid glycine".  

Following that clue we can presume the preservative is the bottle is sodium hydroxymethylglycinate. 

Why Are Some Manufacturers Using Sodium Hydroxymethylglycinate?

Pet parents, having made the links between paraben preservatives and endocrine disease and formaldehyde based preservatives and cancer risk are beginning to demand safer preservatives in products that go on dogs.

In response, parabens and the traditional formaldehyde releasing compounds like diazolidinyl urea, imidazolidinyl urea, quaternium-15, and DMDM hydantoin (often written as DMDH hydantoin) are being replaced.

Enter a preservative you may not have heard of: Sodium Hydroxymethylglycinate (also called Sodium HMG).

As opposed to the above formaldehyde releasing compounds that slowly release formaldehyde over time, sodium hydroxymethylglycinate only releases small amounts of formaldehyde under certain conditions.

Some facts about sodium hydroxymethylglycinate:

• The European Union has permitted sodium hydroxymethylglycinate at concentrations up to 0.5% in human products.
• It is a very effective preservative.
• It is based on the naturally occurring amino acid glycine. [Based on is sort of like saying a movie is based on a book. You go to see the movie after having read the book and discover the movie is NOTHING like the book! You feel jilted - as you should!]
• From the starting base of glycine, sodium hydroxide in water is mixed with formaldehyde - going through synthetic reactions before it is sodium hydroxymethylglycinate. Since it goes through synthetic reactions, it is a synthetic compound.
• Even at concentrations less than 1% it has been shown to cause skin and eye irritation as well as allergies.
• It stinks. It is traditionally found in products that contain synthetic fragrance as they can mask the smell.
• It is typically not used with truly natural products as it can cause discoloration with essential oils - lemongrass will be dark brown for example. 
• It can react with proteins in truly natural products and break down - releasing formaldehyde so it is typically used in synthetic, not truly natural, products. 
• Under certain conditions it can release formaldehyde.
• There is not a lot of research available on this ingredient.
• Dogs who are sensitive to formaldehyde will be sensitive to this ingredient. 

While sodium hydroxymethylglycinate is "safer" than many of the formaldehyde releasing ingredients that over time release formaldehyde and it is "safer" than paraben preservatives, the lack of available research combined with the potential for formaldehyde release (albeit low), and the potential for allergies and skin / eye irritation makes this a preservative we won't be using in 4-Legger products! I guess it is just as well it is not approved for use in USDA certified organic products!