Tonya McKay of NaturallyCurly writes;

Propylene glycol is an ingredient found in many personal-care products, including shampoos, hair conditioners, and leave-in styling products. It is widely used because of its relatively low cost and versatile nature. Its inclusion in a formula can fulfill a variety of purposes, which makes it a popular choice by the cosmetics chemist. However, some manufacturers have recently made the decision to no longer include propylene glycol in their products.

My speculation is that this is possibly due to misinformation and propaganda circulated on the Internet, and elsewhere in the interest of marketing “natural” products. I am an avid supporter of using natural products whenever possible. and of avoiding putting toxins into our bodies whenever possible or practical. But I get frustrated by the dissemination of inaccurate and incomplete information in an attempt to frighten consumers into using different products. In this article, I seek to clear up some misconceptions about this chemical.