Curl Rehab doesn't have the usual "protein", "hydrolyzed", or "amino acids" that are straight up proteins or pieces of a protein, but it does have herbal extracts. Any herbal extracts have trace amounts of protein, because plants contain a bit of protein. So, they can act like proteins for people whose hair is protein sensitive. See here.

Also, if you don't want to shell out for a shower filter yet, you might try rinsing with distilled water first. If that helps, then opt for a shower filter.
CG since 11/2011
2c /3a F /Mii, low porosity

Spring Products /Routine:
Clarifying: Herbal Essences Tealightfully Clean
Low Poo: Renpure Luxurious Argan Oil
Co-washes: Suave Naturals Tropical Coconut or Daily Clarifying
RO:
Tresemme Expert Selection Perfectly (un)Done, Cure Care, Suave Tropical Coconut or Daily Clarifying
LI (if needed):V05 Kiwi Lime Squeeze, V05 Strawbery
Renpure Brazilian Keratin Straightening (old formula), Cure Care
Stylers: LALSG
PT: IAGirl's as needed