I do think sulfites are the safest of all.
I read that carbocyestine was thio based which is very interesting. I do like the QOD Max Organiq treatment because there are no fumes. Here are the ingredients:
Composition: Aqua, Cetearyl Alcohol, Glycerin, Behentrimonium
Chloride, Paraffinum Liquidum, Hydrolyzed Wheat Protein (And) Methicone (And) Polyquaternium-10 (And) Carbocysteine, Polyquaternium7, Hidrolized Keratin, Amodimethicone, Trideceth-12, Peg-7 Glyceryl Cocoate, Hydrolyzed Rice Protein (And) Sodium Benzoate, Theobroma Cacao(Cocoa), Extract Parfum, Cetrimonium Chloride, Bht, Methylchloroisothiazolinona (And)Methylisothiazolinone, Ci 77400.