Silicones often create the illusion of healthy hair, while your hair is damaged and dried out. This way you don’t give your hair what it needs. If you stop using silicone, you are often suddenly confronted with the true state of your hair, and that is why many people quickly resort to silicone.

In some cases, silicone can also conceal your hair texture. They weigh your hair, so curls have less chance.

Unfortunately : There is no simple answer to this particular question ; most especially without further (much more detailed) additional information.

Generally Speaking : There are almost 50 (or so) different classes of Polyquaternium Compounds , which are currently listed as being 'Acceptable' for use in Cosmetic Formulations (as per INCl Research).

However : The appearance of a particular Chemical in an 'Acceptable Substances List' of the International Nomenclature for Cosmetic Ingredients , (INCI) , does not necessarily mean that it is Totally Safe (let alone 'Without Blemish').

Concerning Polyquaternium-18 : I would strongly suggest that you duly seek Expert Professional Guidance , specifically from a Qualified Clinical Toxicologist.

Polyquaternium Compounds fundamentally tend to have rather substantial amounts of Ammonium Ions in them ; and I (personally) am not really a Very Big Fan of such 'Ammonium-Based' Cosmetic Ingredients.

Whatever The Case : (Please) Tread (Quite) Carefully.

Good Luck !

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Professor Obi