It’s estimated that by 2030 there will be 22.2 million new cancer diagnoses worldwide each year [1]. As more accurate methods for diagnosing cancers become standard practice, greater emphasis is put on eliminating preventable cancers. The air in our homes is filled with potentially carcinogenic compounds released by:

• Air fresheners
• Detergents
• Fabric softeners
• Disinfectants
• Deodorants

The lifetime risk of cancer from air pollutants, including those from indoor cleaning products, is estimated to be between 6 to 10 people in every 10,000 [2]. A study published in 2010 identified that women who extensively used cleaning products, were twice as likely to have been diagnosed with breast cancer [3]. This article reviews the most common ingredients in cleaning products, and the evidence for their ability to cause cancer.

How Are Cancer Causing Ingredients Classified?

It can be difficult to determine the cancer risk of an ingredient, with the FDA and EU frequently coming to different conclusions. Both regulatory bodies review reports published by the World Health Organization’s (WHO) independent ‘International Agency for Research on Cancer’ (IARC), which classifies compounds into five categories of carcinogenicity (Table 1). The full monographs can be viewed at [4]: www.monographs.iarc.fr/ENG/classification

Classification	Definition
Group 1	Carcinogenic to humans
Group 2A	Probably carcinogenic to humans
Group 2B	Possibly carcinogenic to humans
Group 3	Not classifiable as to its carcinogenicity to humans
Group 4	Probably not carcinogenic to humans

Table 1. WHO classifications for carcinogenic compounds.

Cancer Causing Chemicals Found in Cleaning Products

Most households use multiple cleaning products, and the number of possible carcinogenic ingredients could be in the hundreds. Most of these ingredients will be in insignificant concentrations (especially for people living in big, polluted cities). Below is a summary of evidence for common ingredients used in cleaning products (this is not a full toxicology review, and an ingredient can be harmful without causing cancer).

1. Phthalates (e.g. dibutylphthalate, diethylphthalate)

Used for: A plasticizer used to soften plastics, stabilize fragrances, and found in many aerosol air fresheners. Phthalates are not chemically bound to plastics, and so can leech from plastic packaging.

WHO Classification: 2B (possibly carcinogenic to humans)

Ingredient Labels: Commonly only listed as ‘fragrance’ or ‘perfume’

Evidence: Many everyday items contain phthalates, with low levels present in children’s toys, infant formula, and the enteric coatings of medications; phthalates can be detected in the urine of most adults [5]. A 2010 study showed significantly higher levels of urinary phthalates in women with breast cancer [6]. In laboratory studies, phthalates have been shown to imitate estrogen (‘xenoestrogens’) and generate genomic instability, which may explain the increased breast tumor growth seen in laboratory studies [7].

2. Chlorinated Bleaches (e.g. sodium hypochlorite)

Used for: Household bleaches are used in cleaning products to disinfect, remove stains, and deodorize.

WHO Classification: 3 (not classifiable as to its carcinogenicity to humans)

Ingredient Labels: ‘Bleach’, ‘bleaching agents’, ‘chlorine-based bleach’

Evidence: There no evidence to suggest that chlorinated bleaches are directly carcinogenic, although regular inhalation has been associated with fatal chronic obstructive pulmonary disease [8]. There is concern that chlorinated byproducts (trichloromethane and tetrachloromethane) may be released into the air when using bleach. These can cause liver, kidney, and bladder cancers, but at concentrations higher than would expected to be released by bleach (e.g. contaminated drinking water) [9].

3. Parabens (e.g. methylparaben, ethylparaben)

Used for: Used as preservatives in a wide range of household products, parabens inhibit the growth of bacteria and fungus, prolonging shelf-lives.

WHO Classification: Not listed

Ingredient Labels: ‘Preservatives’, or those ending in ‘-paraben’ (‘methylparaben’)

Evidence: Like phthalates, parabens have been shown to be xenoestrogens, and are detectable in many urine samples [10]. Since the 1990s, evidence has suggested that parabens can stimulate growth of breast cancer cells, and in 2004 unmetabolized parabens were identified in human breast cancer samples for the first time [11, 12]. A 2011 study correlated paraben concentration to damaged sperm DNA [13]. Parabens are known to stimulate cancer cells at high doses in the short-term, but it’s still not clear if low-dose accumulation can cause cancer in humans [14].

4. Quaternary Ammonium Compounds (e.g. benzalkonium chloride, tetraethylammonium bromide)

Used for: Cationic surfactants used to reduce surface tension, dispersing dirt, increasing the effectiveness of detergents and fabric softeners. Commonly used as preservatives.

WHO Classification: Not listed

Ingredient Labels: ‘Preservatives’, ‘benzalkonium chloride’, ‘quaternium-15’

Evidence: Quaternary ammonium compounds are widely used as preservatives in pharmaceutical eye drops and nasal sprays, and at higher concentrations in shampoos. The evidence for carcinogenicity is controversial, and currently lab-based. In 2006 a study showed DNA damage in exposed lung tissue [15], backed by a 2007 study showing DNA damage in liver and white blood cells [16]. In contrast, a 2005 study found no evidence of cancer activity in mammalian cells [17].

5. Linear Alkylbenzene Sulfonates (LAS)

Used for: Anionic surfactants used to reduce surface tension, dispersing dirt, increasing the effectiveness of cleaning products. Commonly found in laundry detergents.

WHO Classification: Not listed

Ingredient Labels: ‘Anionic surfactants’, ‘linear alkylbenzenesulfonates’, ‘LAS’

Evidence: Since the late 1980s, concern has been raised on the accumulation of linear alkylbenzene sulfonates (LAS) in the environment. In treated sewage, LAS concentrations are found between 0.008 – 6mg/mL [18]. LAS is considered non-toxic and non-carcinogenic to aquatic organisms. A 2016 study highlighted the lack of human data and found that at very low concentrations (1-15parts per million) LAS increased the growth rate of colon tumor cells in the laboratory [19].

6. Phenols (e.g. 2-phenylphenol (OPP))

Used for: Phenols are used in low concentrations as preservatives in many household products, and in higher concentrations as disinfectants (hospitals use phenolic disinfectants to sterilize medical equipment).

WHO Classification: 3 (not classifiable as to its carcinogenicity to humans)

Ingredient Labels: ‘Preservatives’, ‘phenols’, ‘o-phenylphenol’, ‘phenylphenate’

Evidence: The evidence for 2-phenylphenol (OPP) carcinogenicity is of generally low quality, especially in humans. Rats fed 0.5% to 4% OPP in the diets over 13 weeks developed the early signs of bladder tumors, a result replicated in other rat studies – but notably, not in other species [20, 21]. In two humans fatally exposed to 10grams of OPP, toxic effects were noted on bladder linings [22]. In contrast, OPP is rapidly excreted from the human body, and so the accumulation of low doses is unlikely – even on repeated exposure [23].

7. Triclosan (TCS)

Used for: A preservative used to prolong the shelf-lives of detergents, by inhibiting the growth of bacteria and fungus. The effectiveness of triclosan has been questioned by the FDA, with a risk of promoting bacterial resistance without inhibiting growth.

WHO Classification: Not listed

Ingredient Labels: ‘Preservatives’, ‘triclosan’, ‘TCS’

Evidence: The widespread use of triclosan in household and personal care products make it one of the most common pollutants worldwide, detectable in aquatic life and human breastmilk [24]. The compound is estrogenic and androgenic, and so may disrupt hormone regulation, but baboons given 300mg/kg/day for a year in 1975 experienced no carcinogenic or other abnormal effects (other than intermittent diarrhea) [25]. A 2010 review concluded that triclosan is not carcinogenic to humans [26].

8. Crystalline Silica

Used for: Crystalline silica is one of the primary ingredients used to produce the ‘silicate’ surfactants found in some detergents. The ingredient can also be used to manufacturer anticaking agents used in detergent powders (aluminium silicate) and builders to prevent the formation of soap scum (sodium aluminosilicate).

WHO Classification: 1 (carcinogenic to humans)

Ingredient Labels: Ingredients ending in ‘silicate’ were likely manufactured using crystalline silica

Evidence: The evidence for crystalline silica causing cancer is robust, with many large-scale, case-control human studies. Occupational silica dust exposure increases the risk of lung cancer from between 1.3 – 3 times [27]. The risk for ingredients manufactured from crystalline silica is less extensively studied, but silica dust causes lung cancer due to repeated exposure, much like asbestos – silicates in cleaning products do not have this characteristic.

9. Ethanolamines (e.g. diethanolamine (DEA), triethanolamine (TEA))

Used for: Commonly used as emulsifiers to bind water-soluble and fatty ingredients in cleaning products like laundry detergents, washing liquids, and hand sanitizers.

WHO Classification: Diethanolamine 2B (possibly carcinogenic to humans); triethanolamine 3 (not classifiable as to its carcinogenicity to humans)

Ingredient Labels: ‘Nonionic surfactants’, ‘diethanolamine’, ‘DEA’, ‘triethanolamine’, ‘TEA’,

Evidence: The carcinogenicity of the ethanolamines is thought to be due to their structural similarity to choline, an essential nutrient produced in the liver. In animal studies, there is evidence for this link, and long-term accumulation of low-dose diethanolamine has been shown to cause the formation of liver and kidney tumors [28]. Choline is essential for neuronal development, and in mice, diethanolamine accelerates cell death in fetal neurons [29]. There is very little evidence for the carcinogenic effects of ethanolamines in humans, and the WHO classification is based on animal studies.

10. 1,4-Dioxane

Used for: A volatile organic compound (VOC), 1,4-dioxane is used as a solvent in the manufacture of many ingredients in cleaning products. The compound is not specifically added by manufacturers but may be present as a contaminant.

WHO Classification: 2B (possibly carcinogenic to humans)

Ingredient Labels: As a contaminant will not be listed on ingredient labels

Evidence: 1,4-dioxane concentrations in personal care and cleaning products are becoming increasingly concerning because the compound is rated as possibly carcinogenic by both WHO and US EPA. These classifications are from animal data concluding exposure significantly increases the risk of liver, gallbladder, and nasal cancer [30]. Three small human studies (less than 200 people) published in the 1970s evaluating historic 1,4-dioxane exposure found no increased cancer risk [31-33]. Manufacturers are not legally required to remove 1,4-dioxane, although the FDA monitors levels.

11. 2-Butoxyethanol

Used for: Like 1,4-dioxane, the compound can be used as an industrial solvent in the manufacture of ingredients in cleaning products. 2-butoxyethanol can also be added directly to cleaning products as a surfactant.

WHO Classification: 3 (not classifiable as to its carcinogenicity to humans)

Ingredient Labels: ‘Nonionic surfactants’, ‘2-butoxyethanol’, ‘ethylene glycol’

Evidence: 2-butoxyethanol is strongly linked to cancer in mice, but not in humans. In mice, even inhalation exposure to 2-butoxyethanol increases the risk of forestomach and liver cancers [34]. These are not seen in humans, due to the lack of a forestomach and mice susceptibility for the specific type of liver cancer (humans do not experience red blood cell breakdown in response to the compound like mice).

12. Polychlorinated Biphenyls (Endocrine Disruptor)

Used for: Not directly added to detergents, but there is a risk that polychlorinated biphenyls may be produced as a byproduct of the manufacturing of detergent ingredients.

WHO Classification: 1 (carcinogenic to humans)

Ingredient Labels: As a possible contaminant will not be listed on ingredient labels

Evidence: The use and production of polychlorinated biphenyls has been banned in most countries since the early 1980s due to their direct genotoxic and mutagenic activity, known as ‘dioxin-like’ [35]. Large population studies repeatedly identified polychlorinated biphenyls as an occupational exposure correlated with diagnoses of melanoma, breast cancer, and non-Hodgkin lymphoma [36]. In addition, the compounds are known to alter thyroid function and have estrogenic activity (endocrine disruptors).

How Real Are the Risks?

It can be difficult to establish how likely a compound is to cause cancer. Without human trials, the risk is extrapolated from lab results, theoretical mechanisms, and retrospective epidemiological studies. For the compounds listed above, a WHO classification of 1, 2A, or 2B are a reasonable cancer risk in sufficient concentrations, and exposure should be reduced if possible.

It’s even more difficult to say that a compound doesn’t cause cancer. For several of the compounds above, there is little robust evidence to suggest they cause cancer, but this doesn’t exclude the possibility. Only one compound out of 1,067 WHO monographs is Group 4, and ‘probably not carcinogenic to humans’ (‘caprolactam’, which is used to make plastics) [3].

Are There Alternatives?

If using commercial cleaning products, the best way to avoid the most harmful ingredients is to check the product is ‘-free’ of the ingredient (e.g. ‘phthalate-free’ will normally be prominently displayed). This is more difficult for compounds used in manufacturing, such as crystalline silica. For these, the only way to avoid exposure is to use cleaning products with fewer, safer ingredients.

A simpler cleaning product is baking soda and vinegar, with warm water. This has the advantage of avoiding potentially carcinogenic ingredients, but it can be difficult to remove tougher stains. There are several ‘natural’ cleaning products that only contain a few ingredients, but these are generally more expensive, and care needs to be taken to ensure the ingredients are safer.

Most people will find it difficult to eliminate all commercial cleaning products from their day-to-day lives, and so some practical steps to reduce carcinogen exposure include:

• Only use cleaning products in well-ventilated areas
• Stand the recommended distance away when using cleaning products
• Use the smallest quantities possible, and only for difficult to remove stains
• Avoid using aerosol products that pollute the air (e.g. air fresheners)

Summary

Over a lifetime of exposure, there are a vast number of variables that affect an individual’s cancer risk. It is incredibly difficult to establish the role of cleaning products on the incidence of cancer – and more importantly, which ingredients increase the risk of specific cancers in different populations. The most practical way to reduce the risk is to sparingly use cleaning products, using milder alternatives where possible, and always follow the manufacturer recommendations.

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