Understanding the Scent of Coco-Betaine

It is normal for some raw materials used in cosmetic formulations, including Coco-Betaine, to have a distinct odor. The "rancid" smell you are noticing is a characteristic scent of this ingredient.

Many chemical raw materials have inherent smells, which can sometimes be quite strong and noticeable, even at low concentrations in a final product.

As mentioned in the forum reply, the standard industry practice to address the natural odor of ingredients like Coco-Betaine is to incorporate fragrance into the formulation. The fragrance helps to mask or cover the raw material scent, making the final product more pleasant to use.

Creating truly "unscented" cosmetic products can be challenging precisely because formulators need to work with the natural odors of various ingredients without using fragrance to hide them.