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

Go To Products /Routine:
Clarifying: Suave Essentials Strawberry
Low Poo: Renpure Luxurious Argan Oil
CO: Suave Essentials Strawberry, V05 Kiwi Lime
RO /LI: Tresemme Perfectly (un)Done, Cure Care, V05 Kiwi Lime Squeeze, Suave Essentials Strawberry, Renpure Brazilian Keratin (old formula)
Stylers: LALSG, AIF, HETT, Suave Professionals Firm Control
PT: IAGirl's as needed