Studies / Toxic Ingredients

Propylene Glycol Toxicity; An Assessment

Today, millions of people use hair dyes on regular basis, without knowing the negative aspects of the chemicals that they are applying to their skin.. It’s really very difficult to know the extent and frequency of chemical ingredients used in hair dyes and associated health risks.Most companies do not even talk about quantities of ingredients in their formulas. Studies performed during the last few decades by clinicians, scientists and various other Cosmetics Regulatory Councils (US Food and Drug Administration and European Cosmetic Directive etc.) have recommended that some of the ingredients in hair dyes are potentially toxic and can cause acute, subchronic, reproductive and genetic toxicity and carcinogenicity. Chemical ingredients such as propylene glycol, thioglycolates, sulfites, parabens, ethanolamines, have been found to be linked to a host of several medical conditions, including various types of allergic conditions, cancers, respiratory issues and infertility.
Propylene glycol (PG) is among one of these important ingredients, commonly used in personal care products including hair dyes. Propylene glycol represents one of the most versatile and widely used solvent that finds applications in pharmaceuticals, food, cosmetic and chemical industries. Today, it has become a popular choice of the cosmetics chemist, without considering their toxicology and epidemiological relevance. In cosmetic products, the concentration of propylene glycol is up to 73% and is an important ingredient in thousands of cosmetic products. Propylene
glycol, or 1, 2-propanediol belongs to the category of aliphatic alcohol, with two alcohol (hydroxyl) groups (-OH). It is a clear viscous colorless and odorless liquid with a slightly sugary flavour. It is readily miscible in water and hygroscopic in nature and derived from petrochemical sources and chemically inert. The family comprises monopropylene glycol (MPG), dipropylene
glycol (DPG), tripropylene glycol (TPG) and polypropylene glycol, including tetra-rich poly propylene glycol (PPG). The controversy regarding the use of propylene glycol has led to clinical studies for its toxicity profile and epidemiological evaluation at cellular, tissue and animal model levels and also at human subjects. EcoColors does not and will not test on animals. But scientists
in the past have and here are their results;
Studies conducted to evaluate the effect of polypropylene glycol on the reproductive capacity of male and female rats have shown decreased fertility, and reduced ovary weights in maternal rats.
Mucous membrane and skin irritation has also been observed in humans when administered orally. Besides, it also results in skin sensitization reactions and skin rashes. In human subjects, blepharospasm, immediate transitory stinging, and lacrimation were observed after application of polypropylene glycol to the eye. Results also indicate severe effects on the central nervous
system and metabolic disruptions by the use of propylene glycol when administered via the oral route or by injection. Acute toxicity symptoms to high doses of propylene glycol taken orally include CNS depression or narcosis. In mice and rats, these symptoms comprise ptosis (sinking down of an organ), decreased spontaneous motor activity, limb/body tone, respiration, and ataxia (inability to coordinate muscle activity during voluntary movement). Haematological effects have also been conducted on adult female albino Wistar rats by single oral doses of propylene glycol.
Results indicate decreased packed cell volume for up to 2 days, mainly due to hyper-osmolality of the plasma, and altered morphology of erythrocytes. High doses of propylene glycol are also associated with cardiovascular effects including sinus arrhythmia (abnormal heart rhythm); tachycardia (rapid heart rate); irregular heart rate and tachypnea (rapid breathing).
Comparative toxicity studies of ethylene glycol and propylene glycol draw the conclusion that both the substances cause acute effects, and developmental, reproductive, and kidney toxicity, where the toxicity of ethylene glycol exceeds over the propylene glycol toxicity. Apart from this, propylene glycol exposure is associated with skin sensitization potential and reversible hematological
changes in laboratory animals. Toxicity studies of propylene glycol performed by Department of Medicine, University of Connecticut, and Farmington, USA has suggested that short term, high intravenous dose of Propylene glycol could be toxic. These studies confirmed that renal insufficiency, hepatic dysfunction, metabolic acidosis and sepsis-like syndrome are common toxic effects
followed upon propylene glycol infusion. According to the reports of “The International Agency for Research on Cancer”, during manufacturing process contamination of propylene glycols with quantifiable amounts of human carcinogen 1,4-dioxane was observed. Studies related to personal care products by U.S. researchers indicate the presence of 1,4-dioxane as a contaminant in 46 of
100 “natural” or “organic” products. Besides, propylene glycols themselves show the genotoxic effects. They are also responsible for irritation and systemic toxicity when applied on broken skin and hence may not be safe for use as concluded by the industry panel. Since PEGs aid in enhancing the permeability of the skin, it allow for greater absorption of the cosmetic products including
harmful carcinogens.
There has been a conflict over the use of propylene glycols due to the contradictory results based on the usage of its different concentrations. Although, the Cosmetic Ingredient Review Expert Panel has recommended a concentration of less than 50% to be used in cosmetics; the large data set suggests that this concentration is sufficient to provoke allergic reactions in patients suffering
with eczema and other skin allergies and thus complicating the situation. Human exposure to the propylene glycols occurs through multiple routes. The average daily exposure to these propylene glycols can occur through oral route, dermal or inhalation routes (mainly in occupational settings). Kidneys play important role in the excretion of approximately 30%-45% of the administered propylene, thus are the most vulnerable. The use of propylene glycols is also related to acute poisoning with symptoms ranging from drowsiness to stupor, deep unconsciousness, and coma,
hyper-osmolality of serum, lactic acidosis, and hypoglycaemia. It has been observed that metabolism of these compounds follow the common pathways, and a consistent profile of toxicity is observed. Acute intoxication, systemic injury or central nervous system (CNS) depression occurs in rats, cats, dogs, rabbits and adult humans at high doses of propylene glycol exposure.
Propylene glycol displays an irritating effect when it comes in direct contact with eyes, mucous membranes and on prolonged exposure to skin. Furthermore, the safety assessment did not take into consideration of the specific polypropylene glycol chain lengths that may play an important role in the toxicology associated with these products. This warranties the deep insights into toxicological profiles and epidemiology of this family of compounds.
In true words, the current debate of propylene glycol use is regarding the quantity of propylene glycols not the toxicity. According to proponents and followers of propylene glycols, infrequent use of propylene glycols at low concentration does not pose any negative health effect. But, question regarding the frequent use at high concentrations remains unanswerable. The biggest threat
lies in the usage of propylene glycols over the years in a number of formulations including hair dyes and cosmetics, thus making it difficult to keep an eye on its intake. This results in a real and nearby alarming danger that may cause health complications to sky rocket. The decision for its inclusion should be reconsidered in the light of its recurrent use and continuously emerging studies.
The intrinsic human desires to improve one’s appearance, needs the awareness to appreciate the pros as well as cons, and make an educated choice for alternatives.
Suggested Literature

Propylene glycols: Wikipedia information.

Propylene Glycol: The Good, the Bad and the Alternatives. Article

The Truth and Fiction about Propylene Glycol. Article

Fowles, J. R., M. I. Banton, et al. (2013). “A toxicological review of the propylene glycols.” Crit Rev Toxicol 43(4): 363-390. Abstract

Kulo, A., J. N. de Hoon, et al. (2012). “The propylene glycol research project to illustrate the feasibility and difficulties to study toxicokinetics in neonates.” Int J Pharm 435(2):


LaKind, J. S., E. A. McKenna, et al. (1999). “A review of the comparative mammalian toxicity of ethylene glycol and propylene glycol.” Crit Rev Toxicol 29(4): 331-365.Abstract

Pillai, U., J. C. Hothi, et al. (2012). “Severe Propylene Glycol Toxicity Secondary to Use of Anti-Epileptics.” Am J Ther.Abstract

Sampathkumar, K. and S. Yesudas (2009). “Hair dye poisoning and the developing world.” J Emerg Trauma Shock 2(2): 129-131. Abstract

Spencer, P. J., J. W. Crissman, et al. (2002). “Propylene glycol monomethyl ether (PGME): inhalation toxicity and carcinogenicity in Fischer 344 rats and B6C3F1 mice.” Toxicol Pathol

30(5): 570-579. Abstract

Yaucher, N. E., J. T. Fish, et al. (2003). “Propylene glycol-associated renal toxicity from lorazepam infusion.” Pharmacotherapy 23(9): 1094-1099. Abstract

Yorgin, P. D., A. A. Theodorou, et al. (1997). “Propylene glycol-induced proximal renal tubular cell injury.” Am J Kidney Dis 30(1): 134-139.Abstract

Zar, T., C. Graeber, et al. (2007). “Recognition, treatment, and prevention of propylene glycol toxicity.” Semin Dial 20(3): 217-219. Abstract

Fiume, M. M., W. F. Bergfeld, et al. (2012). “Safety assessment of propylene glycol, tripropylene glycol, and PPGs as used in cosmetics.” Int J Toxicol 31(5 Suppl): 245S-260S.


2 thoughts on “Propylene Glycol Toxicity; An Assessment

  1. After vaping PG I can confirm that it does cause hearing damage and heart palpitations in higher concentrations. There can also be a delayed reaction, so you may not correlate the symptoms with the exposure.

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