Which Ingredients to Avoid With the Curly Girl Method

Snape's hair has product build up.

With the Curly Girl method, you don't want to put anything in your hair that cannot be removed by a conditioner wash (cowash).  The first and most important thing to avoid is silicones (often referred to as cones in the cyber hair care universe).  Some silicones are O.K. to use.

How to identify a silicone?  Silicones end in -cone, -conol, or -xane.  Don't be fooled by ingredients that end in -one, those are usually preservatives.  Silicones cannot be removed by cowashing, and should be avoided with the Curly Girl (CG) method.

Partially Water Soluble Silicones- Partially water soluble cones are easier to remove.  IMHO, if you use a non sulfate shampoo (low poo), you don't need to worry about water soluble silicones. Amodimethicone (A.K.A the A-cone) is the one most commonly seen.  I got a lot of the info in this post from this link.
                                      Amodimethicone
                                      Trimethylsiylamodimethicone
                                      Behenoxy Dimethicone
                                      Stearoxy Dimethicone

Cyclo-silicones-  These evaporate off the hair.  In the process of evaporating, they may cause the cuticle to buckle.  At one point on the message boards of NaturallyCurly.com, people thought the cyclo-silicones were building up.   They weren't actually building up, the change in the way their hair felt was from the buckled cuticle.  The Curl Chemist says a low poo should restore the hair.  See this Curl Chemist article for more info.
                                      Cyclomethicone
                                      Cyclopentasiloxane


Water Soluble silicones-  These rinse right off of your hair and are allowed in the CG method.  If your hair is fine and very prone to being weighed down, you may still want to avoid them.  Water soluble silicones weigh done some fine hair.   The first two on the list are the most common.
                       Anything with a PEG- or PPG- in the name.
                       Dimethicone Copolyol
                       Hydrolyzed Wheat Protein Hydroxypropyl Polysiloxane
                       Lauryl Methicone Copolyol

Mineral Oil (A.K.A. petrolatum)-  Some people can use this without any problems.  Others, (like me) find it hard to remove.  It makes my hair oily and heavy.  If you are trying a mineral oil containing product, you may want to try it on a small section/curl first.  That way if things go wrong, you don't have a whole greasy head.

Castor Oil, PEG castor oil-  Same ruled apply as for mineral oil.  Straight castor is popular for hair care to add moisture (mostly with type 4 kinky/curly hair).  I've read there is different qualities of castor oil that make a difference.  I don't know too much about using the oil straight.  I'm more familiar with this as an ingredient.  Works for some, hard to remove for others.  PEG castor oil is easier to remove.  My hair hates castor oil in all forms.

Polyquats-  Which polyquats are likely to build up  depends on which expert you ask.  All agree that polyquat-4, common in mousse, is easy to remove.  As a general rule, the larger the number the harder the polyquat is to remove.  These links have more info on polyquats in hair products.
Curl Chemist on Polyquats
No-Poo Jillipoo talked to several experts about polyquats.

So, if you avoid everything on this list, does that you will never get build up?  Nope.  Some random things build up for some people.  Jojoba oil builds up for me.  Also cationic conditioners are meant to adsorb (cling) to the hair.  They are usually washed off.  But sometimes, some continue to cling to the hair and build up.  A low poo will remove this build up.  This link has more on how conditioners can build up.