The Verdict List
Use with caution

1,4-Dioxane

Last reviewed

What it is

1,4-Dioxane is a synthetic industrial chemical that shows up in shampoos, body washes, bubble baths, liquid laundry detergent, and dish soap - but nobody puts it there on purpose. It forms as an unwanted byproduct of "ethoxylation," a manufacturing step that reacts ethylene oxide with other raw materials to make harsh detergents gentler on skin and eyes. The classic example is sodium lauryl sulfate (a strong, sometimes irritating cleanser) being converted into sodium laureth sulfate (SLES) - milder, but the "eth" in the name signals the ethoxylation step that can leave trace 1,4-dioxane behind. The same byproduct can turn up wherever you see "PEG," "polyethylene glycol," "polysorbate," "-eth-," or "-oxynol-" ingredients, since they're all made the same way. It's a manufacturing contaminant, not a functional ingredient - it does nothing for the product.

Why it's flagged

Regulators classify 1,4-dioxane as a likely carcinogen based on animal data: the International Agency for Research on Cancer put it in Group 2B ("possibly carcinogenic to humans") after it caused liver tumors in mice, and nasal, liver, and peritoneal tumors in rats; the U.S. National Toxicology Program lists it as "reasonably anticipated to be a human carcinogen" in its Report on Carcinogens; and EPA's own IRIS toxicological review (finalized 2013) characterizes it as "likely to be carcinogenic to humans," again based on sufficient animal evidence and inadequate human epidemiological data. Because it's a trace, non-functional contaminant rather than a deliberately added ingredient, FDA's cosmetic labeling rule (21 CFR 701.3) generally exempts it from having to appear on the ingredient list at all - which is exactly why label-reading alone won't catch it; you have to recognize the ethoxylated "indicator" ingredients instead. FDA has monitored dioxane levels in cosmetics since the early 1980s and pushed manufacturers toward a purification step called vacuum stripping; its own surveys show average levels falling sharply, from roughly 50 ppm in 1981 to about 19 ppm by 1997, with the large majority of products by 2018 testing under 10 ppm (only about 2% of children's products exceeded that level). Separately, EPA's November 2024 Final Revised Risk Determination under TSCA for 1,4-dioxane as a whole chemical found unreasonable risk to workers and occupational non-users from cancer and non-cancer effects across most of the industrial/commercial conditions of use it assessed, and it also found unreasonable risk to the general population and fenceline communities - based on cancer risk from 1,4-dioxane in drinking water drawn from surface water contaminated by industrial discharges and by down-the-drain disposal of commercial and consumer products, including laundry detergent and dish soap. It did not find unreasonable risk to the environment (i.e., ecological receptors) from the conditions of use it assessed.

How concerned to be

This is a genuine caution-tier entry, not an avoid-tier one, and the nuance matters: 1,4-dioxane really is classified as a likely/possible carcinogen by IARC, NTP, and EPA, and no regulator has set a level that's officially declared "risk-free." At the trace concentrations actually found in modern rinse-off personal care and household cleaning products - reflecting decades of industry purification improvements and FDA pressure - the exposure picture for an individual using one bottle of shampoo or detergent is quite different from an intentionally-added ingredient at meaningful concentrations. That said, EPA's own November 2024 TSCA determination did find unreasonable risk to the general population and fenceline communities from 1,4-dioxane - not from using these products in your own home, but from the aggregate, population-scale pathway of the chemical reaching drinking water via industrial discharge and down-the-drain disposal of exactly these product categories (laundry detergent, dish soap) at scale. That's a real regulatory finding worth taking seriously as a systemic issue, even though it doesn't change the calculus much for an individual bottle at typical trace levels. New York took this seriously enough to act where federal law hasn't: its Household Cleansing Product Information Disclosure Program requires makers of cleaning products sold in the state to disclose ingredients including nonfunctional byproducts like 1,4-dioxane, and separate DEC regulations (first-in-the-nation, phased in 2022-2023 and finalized in September 2024) cap it at 1 ppm in household cleansing and personal care products and 10 ppm in cosmetics. Outside New York there's no comparable federal ppm cap, so exposure still depends on which brand's supply chain you're buying into. The practical read: don't panic over SLES or a PEG compound on a label, especially in something rinsed off quickly, but if you're trying to minimize exposure - for infants, for leave-on products, or simply across the many ethoxylated ingredients a household uses cumulatively - favor brands that use non-ethoxylated surfactants (like sodium coco-sulfate alternatives or SLS itself, ironically) or that publish third-party dioxane testing, since the ingredient list itself won't tell you.

What it's called on a label

Look for any of these on an ingredient list: Dioxane, 1,4-Diethylene dioxide, Diethylene dioxide, Diethylene ether, p-Dioxane, 1,4-Diethyleneoxide, Sodium Laureth Sulfate, SLES, Sodium Myreth Sulfate, PEG-100 Stearate, Polyethylene Glycol, Ceteareth-20, Oleth-10, Laureth-4, Polysorbate 20, Polysorbate 80, Nonoxynol-9.

Sources

  1. 1,4-Dioxane in Cosmetics: A Manufacturing Byproduct, U.S. Food and Drug Administration (FDA) (2022)
  2. 1,4-Dioxane (Group 2B), IARC Monographs Volume 71, International Agency for Research on Cancer (IARC/WHO) (1999)
  3. 1,4-Dioxane, Report on Carcinogens, Fifteenth Edition, National Toxicology Program (NTP), U.S. Dept. of Health and Human Services (2021)
  4. IRIS Toxicological Review of 1,4-Dioxane (With Inhalation Update) - Summary, U.S. Environmental Protection Agency, Integrated Risk Information System (IRIS) (2013)
  5. 1,4-Dioxane; Supplement to the Risk Evaluation and Revised Unreasonable Risk Determination Under TSCA, U.S. Environmental Protection Agency (TSCA) (2024)
  6. DEC Finalizes Regulations Restricting 1,4-Dioxane in Consumer Products, New York State Department of Environmental Conservation (NYSDEC) (2024)
  7. Household Cleansing Product Information Disclosure Program, New York State Department of Environmental Conservation (NYSDEC) (2018)
  8. 21 CFR Part 701 -- Cosmetic Labeling (incidental ingredient exemption, 701.3), Electronic Code of Federal Regulations / U.S. FDA (2026)