Preservatives: Parabens

Yesterday we took a look at organic acids, including benzoic acid. This is the category under which parabens fall, as they are para-hydroxybenzoic acids. There are five parabens we find in cosmetic products - methylparaben, ethylparaben, propylparaben, butylparaben, and benzylparaben - and two isomers - isopropylparaben and isobutylparaben - and the position of the functional group determines the anti-microbial activity and solubility.

The solubility in water decreases and the preserving activity increases as the chain length of the paraben increases. So methylparaben is very water soluble but not so great a preservative, and butylparaben is more oil soluble and a fantastic preservative. They tend to be more about the fungus fighting powers than the bacterial fighting powers and they are more effective against Gram positive bacteria than Gram negative bacteria.

A quick chemistry lesson here: Meth- means 1, eth- means 2, prop- means 3, and butyl- means 4. If you look at the picture of methylparaben, you'll see there's 1 CH2 at the end of the chain. If you look at the picture of propylparaben, you'll see there are 3 carbons in that chain. With the heptylparaben, there should be 7 carbons on the chain. So when we talk about the chain length increasing, this is what we mean! 

Parabens are incompatible with some proteins, and it's recommended that parabens be combined with other preservatives that have better bacteria fighting abilities. They are stable to heat, but best when added to the cool down phase at lower than 60˚C.

Parabens can be inactivated by non-ionic surfactants, methylcellulose, gelatin, PEG emulsifiers, and proteins, as well as the fatty acid esters of sucrose. This means that non-ionic surfactants that are based on the addition of ethylene or propylene oxide to fatty acids, fatty alcohols, esters, and polyglycols might make our preservative fail to work. Polysorbate 80 is one of the worst culprits for inactivating parabens, possibly due to the formation of complexes through hydrogen bonding. And what about emulsifying wax? Yep, there could be a problem there as it's an ethoxylated emulsifier!

But there's a way out of this problem - the addition of anionic or quaternary compounds to our products can help prevent the inactivation. So adding something like polyquat 7 or using BTMS as the emulsifier should keep our preservative working in a lotion, and it won't be a problem for surfactant mixes as long as you include an anionic surfactant in the product!

The other way out of paraben inactivation is that very few of the preservatives we buy contain only parabens. Of all the ones I've looked at so far, only Liquipar Oil contains only parabens. The rest contain a imidiazolidinyl urea or diazolidinyl urea,  phenoxyethanol, or iodopropynyl butylcarbamate, which will help boost

Parabens do exist in nature, found in Japanese honeysuckle and blueberries, but neither of these are suitable replacements for synethetic parabens found in our preservatives. (There are tests on Japanese honeysuckle as a naturally occurring preservative, but they aren't looking that great!) Check out this link by Anthony Dweck on naturally occurring parabens for more information!

So what's with the safety of parabens? Do they cause cancer? I'm not getting involved in this debate, but I will offer you some information I found on the FDA and American Cancer Society websites.

FDA believes that at the present time there is no reason for consumers to be concerned about the use of cosmetics containing parabens. (Click for the link here.)

But so far, studies have not shown any direct link between parabens and any health problems, including breast cancer. There are also many other compounds in the environment that mimic naturally-produced estrogen. The bottom line is that larger studies are needed to find out what effect, if any, parabens might have on breast cancer risk. (Click for link here.)

For more information, please click for a great PDF on this topic!

Join me tomorrow as we delve into the world of preservatives by taking a look at the urea based preservatives!