Submitted via the FutureDerm.com Facebook page:

Do vitamin C and sodium benzoate form a carcinogen?  I read that somewhere, but I wanted to ask you if it was true.

-T

Dear T,

Without careful examination, this looks like a story worthy of the front page of The New York Times!  Vitamin C and sodium benzoate (a preservative) will together form benzene, which has been associated with causing cancer (International Journal of Occupational and Environmental Health, 2007).  For the ultra-scientific, benzene is associated with causing DNA strand breaks, and high levels of exposure have been associated with acute myeloid leukemia (AML), aplastic anemia, myelodysplastic syndrome (MDS), acute lymphoblastic leukemia (ALL), and chronic myeloid leukemia (CML).(Annual Review of Public Health, 2010).

However, most beauty products contain sodium benzoate in extremely low concentrations – parts per billion or less.

Still, considering the fact that soft drinks also contain very low amounts of benzoates, and 2.5% of 200 soft drinks with vitamin C and sodium benzoate were found to have levels of benzene above allowable levels (FDA, 2007), there is still the moot possibility that some skin care and cosmetics could contain benzene.  So here is what to do:

How to Protect Yourself

High amounts of vitamin C + a high pH (above 3) = significantly reduced benzene production!

Chemical reactions are a lot like meeting a potential partner:  The conditions matter.  Just like dim lighting, a fancy restaurant, and a dozen roses can flip that nerd from accounting from the “friend zone”, so can quantities of chemicals, temperature, and the pH make a world of difference with a chemical reaction.

Such is the case with vitamin C and sodium benzoate.

Benzene does not form at all if you use beauty products with a very high concentration of vitamin C and a low concentration of sodium benzoate (AIB International, 2006).   Why?  Increasing amounts of vitamin C cause for it to act as a free radical scavenger rather than in the sodium benzoate reaction.  (Look at it this way:  Your date offers to take you to a restaurant you despise, and you would have a bad reaction.  But if he offers to take you to the Academy Awards instead, you have a better option, and you’d do that instead.)

Products formulated with a pH of 3 or above are also safer than those with a pH of 2 or less (AIB International, 2006).  And above a pH of 7, no benzene forms at all.  This is unfortunate, because it leaves vitamin C formulations a very narrow window of pH 3.0 to 3.5 to work with, as vitamin C has been shown to work best at a pH of 3.5 or lower (Dermatologic Surgery, 2008).

So you won’t catch me using vitamin C products in non-acidic form, even if they don’t form benzene with benzoates/benzoic acid.  Instead, I simply use concentrated vitamin C products, and I avoid sodium benzoate and benzoic acid together with vitamin C.

Bottom Line

Protect yourself and still maintain efficacy of vitamin C by using products with: a.) high vitamin C; b.) no benzoic acid or benzoates; c.) storing your beauty products in a cool, dark place.

In short, using a product with high concentrations of vitamin C should eliminate the vast majority of benzene formation. Other options include using parabens (which are safe in skin care and cosmetics) instead of preservative systems like sodium benzoate and benzoic acid, both of which form benzene with vitamin C; and keeping your beauty products in a cool, dark place, as higher temperatures and light incite the reaction to benzene (AIB International, 2006).

But let me get on my soapbox for just a minute – this is what the problem is with society’s general distrust of skin care and cosmetics ingredients nowadays.  Databases are automatically flagging studies about parabens.  And despite the fact that I have never spoken to a dermatologist or cosmetic scientist who does not approve parabens for anyone who is non-allergic, the non-scientifically-trained public is demanding products without parabens.  As a result, some manufacturers are using benzoic acid and benzoates instead – and guess what.  They’re an actual problem!  At least, they are when combined with vitamin C. *sigh*

So, for now, avoid products with benzoic acid and benzoates, especially when using vitamin C.