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1.4 - Dioxane

A Conundrum?

There has been a lot of interest recently in a trace contaminant in cosmetics, consumer products, and even food.  The contaminant, 1,4-dioxane, does occur naturally in food (chicken and tomato juice) and is allowed by the FDA as a contaminant in glycerides, polyglycerides of hydrogenated vegetable oils as food additives at levels not to exceed 10 ppm (10 mg/kg).  The same standard was put forth by the National Academy of Sciences in a food additive called polysorbate, and the US EPA allows up to 4 ppm (4 mgs/liter) in drinking water.  The problem is that 1,4-dioxane has been labeled as a “possible” or “probable” human carcinogen by several regulatory agencies whose policy is to label any chemical as a carcinogen that has been shown to be carcinogenic in animal models at any dosing level.

When chemicals are tested to determine if they are carcinogenic, they are tested at dosing levels that produce toxicological effects, including cancer.  If a carcinogenesis bioassay is carried out and does not produce toxicological effects, the bioassay has failed.  In the case of 1,4-dioxane, bioassays have been carried out at dosing levels that overwhelm the metabolic capability of the animal resulting in severe liver damage, including cancer as well as nasal carcinomas.  The nasal lesions result from unmetabolized 1,4-dioxane being exhaled by the animals, thereby damaging the nasal epithelium.  Thus, the bioassays show that 1,4-dioxane is carcinogenic in animal models at dosing levels that are greater than 40,000 times what a consumer might encounter in a shampoo containing 30 ppm 1,4-dioxane. 

1,4-dioxane has been extensively tested to determine if it is a mutagen exhibiting genotoxicity (chromosomal damage).  It is not genotoxic according to the results of numerous and varied assays as is reported by the US FDA, the US EPA, Health Canada, the Australian Government and others.  This is an extremely important issue since genotoxins may produce cancer at low dosing levels; whereas, non-genotoxins that are carcinogenic at high dosing levels may not produce cancer at lower dosing levels.  This is referred to as a threshold effect; that is, the dose-response curve is non-linear at low dosing levels indicating the risk of cancer is either very low or non-existent at low dosing levels.  Studies in rats and mice dosed with 1,4-dioxane show no statistically significant increase in tumors at the lower dosing levels, thereby demonstrating a threshold. Further, these dosing levels are thousands of times higher than what a consumer would be exposed to through the use of a detergent, shampoo, cosmetic or other consumer product containing 1,4-dioxane.

Regulatory agencies like the US EPA, US FDA, OSHA, IARC, Health Canada and others refer to 1,4-dioxane as a possible or probable carcinogen. Any chemical that produces cancer in laboratory animals is labeled as a possible or probable carcinogen as a matter of regulatory policy.  This is done out of an abundance of caution, but it does not suggest that 1,4-dioxane will produce cancer  at any dosing level.  1,4-dioxane is labeled  in this way as part of the regulatory process.  Unfortunately, activist groups see this carcinogen label and immediately believe that they are being poisoned or that their children are going to get cancer as a result of being exposed to trace amounts of 1,4-dioxane; however, this simply is not true.

1,4-Dioxane has been manufactured and used in various processes for many decades, and no study has shown conclusively that it has produced an increase in the incidence of cancer in man. Further, animal studies demonstrate thresholds below which no cancers are observed.  A mode of action recently proposed makes it clear that metabolic overload is responsible for the production of cancer in animal models, and this requires very high dosing levels.

In conclusion, it is my opinion that trace amounts of 1,4-dioxane in consumer products will not result in an increased risk of developing cancer in adults or children, nor will it result in any other toxicological effects.

Richard A Parent, PhD, DABT, FATS, RAC, ERT
Consulting Toxicologist
Consultox Limited (
P. O. Box 1239
Damariscotta, Maine 04543
tel 207-563-2300


In the interest of full disclosure, it should be noted that Dr. Parent is involved in litigation for the defense of products containing 1,4-dioxane.  As a result of this involvement and much study, he is convinced that there is no health hazard related to the use of consumer products containing trace amounts of 1,4-dioxane.

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