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

Autumn Products /Routine:
Clarifying: ACV rinses, Suave Professional Men Deep Clean Peppermint
Low Poo: Renpure Luxurious Argan Oil
Co-washes: VO5 Kiwi Lime Squeeze or Strawberries & Cream
RO: VO5 KLS or S&C, Cure Care
LI (if needed): VO5 S&C, VO5 KLS, Cure Care
Stylers: FSG, L'Oreal Studio Clean gel, Tresemme Flawless Curls Bouncy Curls gel
PT: IAGirl's as needed