Sunday, July 5, 2009
Like trying to scrape gum off a shoe
Months ago, I wrote a post about cationic polymers. Before your eyes glaze over, let me just say that cationic polymers are known by most of us as "polyquats." They are the ingredient names that begin with Polyquaternium and then a number. The numbers express some kind of molecular chain organization.
I had written the post because one of my favorite blogs, The Beauty Brains, had raised concern that cationic polymers attached themselves to hair more stubbornly than silicones, and therefore were potentially more troublesome. I did some research and sort of confirmed that they may have been right. But I didn't dig deep enough.
Yesterday, I slogged my way through my trusty copy of Chemical and Physical Behavior of Human Hair by Clarence R. Robbins. This is not light reading, folks. Quite a bit of it is essentially Greek to me, but now and then, I can figure out the message. And with regard to cationic polymers, I learned just enough to develop a bona fide fear of polyquats.
The message is this: cationic polymers do not necessarily penetrate the hair to a great extent, but they are damn near impossible to remove.
Think of polyquats like gum on the sidewalk and your hair like the bottom of a shoe. When those two meet, it's hard to separate them. Things can get ugly.
Now, the book addressed Polyquaternium 10 in most instances. According to Tonya McKay at NaturallyCurly.com, this is one of the more conditioning cationic polymers and is often added to shampoos to impart softness and manageability. But other polyquats -- specifically those with different molecular weights and chemical structures -- are used in styling products because they adhere better (!) and result in a better hold. Polyquat 10 is favored more as a conditioning additive than a styling/holding one.
(For you geeks out there: "Cationic ingredients in general are highly substantive [resist removal by water rinsing] to hair because of hair's low isoelectric point, which is approximately pH 3.67 in cosmetically unaltered hair, and even lower in bleached hair. Therefore, at any pH above the isoelectric, the surface of hair bears a net negative charge, and positively charged (cationic) ingredients are attracted to it." Chapter 7 )
The news is worse for those who have had chemical services done to their hair because the "holes" created by these services create additional opportunities for cationic polymers to attach themselves. So, if your hair is colored or straightened or otherwise messed with by some sort of chemical, you can expect that polyquats will stay with you for quite some time.
So just how long do they hang around? The experiments cited by Robbins indicated that less than 15% of Polyquat 10 was removed from the hair after soaking in distilled water for 30 minutes. (Note that they used distilled water, though. I don't know whether that might make a difference -- seems like it might?) Salt removes cationic polymers better than water, but it's not clear that you could call that removal "effective": "sodium dodecyl sulfate, analogous to a shampoo, was much more effective, removing more than 50% of the polymer in one minute and nearly 70% in 30 minutes." And get this: "Even after a week in 0.1M lanthanum nitrate solution [also a salt], approximately 40% of the polymer was still bound to the hair."
Salt and surfactants combined with cationic polymers decrease the uptake of them to the hair. So, if you find Polyquat 10 in a shampoo or in a styling product that contains magnesium sulfate (salt), the stuff won't stay on your hair as much. But a small amount will remain. Depending on how often and how much you use the polyquat, and what strength it is in the product, you could be looking at days.
Now, the question is: Is this bad? Are cationic polymers blocking moisture like silicones do? That isn't clear, either from the Robbins book or from McKay's article. But anything that has the potential to build up on your hair and be difficult to remove doesn't seem like something to gravitate to.
I realize that I have simplified this topic considerably and that not all polyquats are the same by any stretch of the imagination (or science!). If you are using stylers and/or conditioners with a polyquat or two in them and your hair feels funny or you can't get it clean, maybe this post will help you figure out why.