I keep seeing people worried about build-up of conditioners on their hair (a lot of times accompanied by information about how a friend of a friend was told by her hair dresser that she had a waxy coating of conditioner on her hair, which the hairdresser proceeded to scrape off with a pair of scissors!) What exactly do we mean by build-up?
Build-up doesn't have a specific definition, but it's understood to be when our hair has a sticky, gummy, or coated feeling. It is also generally understood to take more than one usage of the ingredient or product to cause build-up, although it can happen (theoretically) with one washing. Anything that is substantive to our hair can cause build-up - which is why we use them - meaning cationic quaternary compounds (like BTMS or cetrimonium bromide), silicones (like dimethicone and amodimethicone), and cationic polymers (like polyquat 7 or honeyquat)
What causes build-up? Some ingredients we use can cause build-up, and this isn't helped by the water we use to bathe. One of the main culprits in the feeling of build-up is calcium in our water. It can make hair feel dull and rough. This is one of the reasons we see EDTA in commercial shampoo - EDTA is a chelating ingredient that binds to ions in hard water (sodium, calcium, and other metallic elements) and keeps it from depositing on our hair and scalp. We can include EDTA in our shampoo at up to 0.20%.
Cationic quaternary compounds like BTMS or cetrimonium bromide can potentially build-up on our hair if we are using too much, for instance, intense conditioners as every day or leave in conditioners, and this is increased by the usage of cetyl alcohol in said conditioners, because cetyl alcohol can increase substantivity
We use cationic quaternary compounds because they offer conditioning properties - reduced friction, static, and impact of combing forces, and improved lubricity. The problem arises when we can't remove the conditioner from our hair when we wash it, generally because we aren't using a well formulated, mild, surfactant based cleanser.
Cationic polymers can build up on our hair over time, but if we use a good surfactant based cleanser, they'll be rinsed out during the next washing. If we're using the cationic polymers in a shampoo, they can form a negatively charged complex with excess surfactant that will resist removal. This is one of the reasons we use the surfactant levels we do in a conditioning shampoo - too much excess surfactant can cause this problem - and the reason we don't use a ton of cationic polymers! This negatively charged complex increases with SLS, for some reason, which is another reason to formulate with more gentle surfactants. (Polyquats 6, 7, 10, 11, and 16 are more likely to resist removal than the other polyquats.)
Silicones can build up on your hair if you are using a lot - for instance, in your shampoo, conditioner, leave in conditioner, anti-frizz spray, and heat styling product. The worst culprit is amodimethicone as it is more substantive to your hair than dimethicone or cyclomethicone. Using 2% in a shampoo, then 2% in a conditioner is unlikely to cause build-up, and you really have to be using a lot to get any sort of true build-up from silicones. (And remember, 2% cetrimonium chloride gets rid of silicones - even a lot of them!)
The more damaged your hair, the more potential build-up of the conditioning agents - damaged hair has a higher negative charge, and we know the more negatively charged your hair, the more conditioner is deposited. You want more deposition, but you also need to remove the conditioning agents when cleansing your hair the next time. So if you're using intense conditioners or tons of styling products regularly, make sure you also use a clarifying shampoo (no conditioning agents or silicone) and include some cetrimonium chloride in your creations!
I might regret writing this post as I feel like I'm feeding into the mind-set that all conditioning agents cause immediate build-up: As you can see from this post, they don't. They have the potential for build-up, but potential doesn't equal actuality. If you are using a good surfactant based shampoo with low levels of cationic polymers, and if you aren't using intense conditioners every day, it's unlikely you'll see build-up on your hair. If you are, then consider adding EDTA to your shampoo or conditioner and getting some kind of water softening system (the EDTA is much less expensive!).
You won't see build-up in the form of a waxy coating on your hair - this is an urban legend - but you'll know build-up when you feel it. If you are feeling as if your hair is lifeless and limp, try a clarifying shampoo and see how it feels. Unless you have really hard water, the problem should clear up in one wash!