Vegetable glycerin is a thick, syrupy, sweet liquid that is derived from vegetable oils. This liquid is used as a lubricant emollient and humectant in various cosmetics and skin care products. Vegetable glycerin is also used in hair styling agents and conditioners—to smoothe and soften hair and allow it to retain moisture. It is mostly derived from palm and coconut oils and is commonly available in health food stores and through online merchants. While considered safe for most external applications, the substance is associated with some health hazards, which must be kept in mind before purchasing it or its derivatives.
Vegetable glycerin derived from coconut and palm oil causes reactions in individuals who are allergic to these substances or their byproducts. Some vegetable glycerin products contain preservatives that are added to extend their shelf lives. Sulfite preservatives (compounds of oxygen and sulfur in combination with sodium sulfite or potassium sulfite) are popularly used to maintain the freshness of vegetable glycerin products, including soaps, shampoos and lotions. They produce asthma-like allergic reactions in allergy-prone individuals, the symptoms of which include itching, nausea, dizziness, diarrhea, shortness of breath and hives.
Some synthetic vegetable glycerins, such as propylene glycol, are associated with severe side effects. According to Kevin Woodward in the book “Veterinary Pharmacovigilance,” propylene glycol is toxic to dogs, cats, horses, cattle and other animals. According to Allan B Wolfson and his co-authors, in the book "Harwood-Nuss' Clinical Practice of Emergency Medicine," ingesting propylene glycol brings about alcohol-like effects, and high doses of the substance, when ingested, can result in central nervous system disorders, renal failure and even fatalities in humans.
Vegetable glycerins, including propylene glycol, are known to cause skin irritations. According to Jan E. Wahlberg and her co-authors in the book “Management of Positive Patch Test Reactions,” undiluted 10 percent and 50 percent propylene glycol is a skin irritant, and concentrations as low as 5 percent can also cause irritation. Natural vegetable glycerin, which comprises the active ingredient in many skin care products—including soaps, lotions and face-washes—also causes skin irritation in some users. According to Francine Milford in the book “Aroma Care: Make Your Own Perfume,” vegetable glycerin-based perfumes cause skin allergies in certain people.
Mucous Membrane Irritant
According to D. R. Price in the book “Do You Have Kitchen Disease,” vegetable glycerin can cause irritation to mucous membranes. Shirley Price and Len Price state in the book “Aromatherapy for Health Professionals” that vegetable glycerin irritates the mucous membranes of the genitourinary, respiratory and alimentary tracts, which may cause diarrhea, aches, irritation of the upper airway, wheezing, swelling of the tongue and gastroenteritis.