four Mad About Curl and Waves labeled bottles on wooden surface

 

 

Human and Environmental Toxicity of Sodium Lauryl Sulfate (SLS): Evidence for Safe Use in Household Cleaning Products

 

十二烷基硫酸鈉(Sodium Lauryl Sulfate (SLS))對人體及環境的危害:家用清潔用品的使用安全的科學根據

 

Abstract 摘要

 

Environmental chemical exposure is a major concern for consumers of packaged goods. The complexity of chemical nomenclature and wide availability of scientific research provide detailed information but lends itself to misinterpretation by the lay person. For the surfactant sodium lauryl sulfate (SLS), this has resulted in a misunderstanding of the environmental health impact of the chemical and statements in the media that are not scientifically supported. This review demonstrates how scientific works can be misinterpreted and used in a manner that was not intended by the authors, while simultaneously providing insight into the true environmental health impact of SLS. SLS is an anionic surfactant commonly used in consumer household cleaning products. For decades, this chemical has been developing a negative reputation with consumers because of inaccurate interpretations of the scientific literature and confusion between SLS and chemicals with similar names. Here, we review the human and environmental toxicity profiles of SLS and demonstrate that it is safe for use in consumer household cleaning products.

 

在快速消費品(consumers of packaged goods, CPG)市場中,化學成分對環境的影響是消費者主要關注的其中一項。儘管網路上有非常多有提供詳細資訊的科學研究,但那些複雜的化學名稱及相關知識對於一般人來說實在是難以理解,甚至會有誤解的情況發生。以界面活性劑-十二烷基硫酸鈉來說,許多媒體指出這項物質對環境及人體的健康上有著負面的影響,但這背後並無任何科學證據。這也就是為何我會想做這項研究的原因,除了說明有些從文獻延伸的論述其實並非資料來源作者的本意外,同時讓大眾有了解SLS-這個常用於製造消費性家用清潔品的界面活性劑到底對環境有什麼確切的影響。在過去的數十年來,由於很多人對相關科學文獻內容有所誤解,而且把SLS與類似名稱的化學物有所搞混,讓SLS一直以來都有負面評價。不過在分析它對環境及人體的危害程度後,發現它在家用清潔方面是安全無虞的。

 

Keywords: surfactant, media claims, product formulation, ingredient safety review

關鍵字:界面活性劑、媒體聲譽、產品配方、原物料安全檢測

 

Introduction 緒論

 

Sodium lauryl sulfate (SLS), also known as sodium laurilsulfate or sodium dodecyl sulfate, is an anionic surfactant commonly used as an emulsifying cleaning agent in household cleaning products (laundry detergents, spray cleaners, and dishwasher detergents). The concentration of SLS found in consumer products varies by product and manufacturer but typically ranges from 0.01% to 50% in cosmetic products(1,2) and 1% to 30% in cleaning products.(3,4) SLS can be synthetic or naturally derived. This chemical is synthesized by reacting lauryl alcohol from a petroleum or plant source with sulfur trioxide to produce hydrogen lauryl sulfate, which is then neutralized with sodium carbonate to produce SLS.(5)

 

月桂基硫酸鈉(Sodium lauryl sulfate ,SLS)別名十二烷基硫酸鈉,是家用清潔品(洗衣劑、噴霧洗潔劑、洗碗劑)中作為乳化清潔介質的一種陰離子界面活性劑。在消費性產品中的SLS因著各種的產品類別而有不同的濃度,在妝品和清潔品方面,兩者的濃度分別為0.01-50%(1,2)及1%-30%(3,4)。而這些產品中SLS可能是化學合成或者是天然成分所提煉而成的。分別是從石油及植物提煉出月桂醇後與三氧化硫產生化學反應後產出氫化十二烷基硫酸鈉(hydrogen lauryl sulfate),接著就會與碳酸鈉結合形成SLS(5)

 

SLS (CAS# 151–21–3; MW 288.38 g/mol; pH 7.2) is a nonvolatile, water-soluble (100–150 g/L at room temperature) compound with a partition coefficient (log Pow) of 1.6 – making it a relatively hydrophilic compound.(68) Generally, hydrophilic compounds have a low soil/sediment adsorption coefficient and low bioconcentration factors (BCFs). The BCF for SLS ranges from 2.1 to 7.1.(6,7) Down-the-drain cleaning products release SLS into the environment via household wastewater systems. In the environment, >99% of SLS readily biodegrades into nontoxic components per the OECD 301 standard.(7)

 

SLS(CAS# 151–21–3, 分子量 288克/莫耳, pH值 7.2)是一種能溶於水(在室溫下每一公升可溶解100-150克)的非揮發性化合物,同時由於它的分配係數(partition coefficient)為1.6,我們可以知道它是相對具有親水性的化合物(68)。一般來說,親水性化合物有著低的沉澱物吸收係數(adsorption coefficient)以及生物濃縮係數(bioconcentration factors, BCFs),而SLS的BCFs大約落在2.1至7.1之間(6,7)。講白話一點,當這些清潔用品經由下水道系統,將SLS釋放到環境時,有超過99%的SLS會生物降解成合乎OECD(經濟合作暨發展組織) 301標準的無毒化合物(7)

 

Consumers may be exposed to SLS by using products that contain the ingredient. Exposure to SLS from household cleaning products depends on the frequency of household cleaning activities, which is reported as being 1–2 times per week on average.(9) The intended application of detergents and cleaners should not result in direct contact with product ingredients; however, misuse of the product could potentially cause dermal (skin and ocular) or inhalation exposure.(9) Oral exposure to cleaning products is unlikely but has occurred – mostly in children – because of accidental ingestion.(10) With regular use of cleaning products, the delivered dose of SLS from dermal or inhalation exposure is expected to be low given the low volatility and dermal absorption rate of SLS.(6,7)

 

消費者在使用含有SLS的產品時,可能會接觸到這項成分,但依據使用的頻率而有不同的接觸程度。目前根據統計,以平均來說,每個人每周大約會使用1-2次。(9)儘管使用清潔劑應該不會直接接觸到這項成分,但如果使用的方式有誤,可能會有沾染(肌膚及眼部)或是吸到它的風險(9)。值得注意的是,雖說口部是不太可能接觸洗潔用品,但幼童可能會誤食而會有這樣的狀況(10)。綜上所述,如果正常的使用清潔用品,那麼接觸到SLS的風險其實是很低的(6,7)

 

Since the early 1990s, misconstrued information on the human and environmental toxicity of SLS has led to consumer confusion and concern about the safety of SLS as an ingredient in household products.(11) As scientific literature is inherently vulnerable to misinterpretation by the general public, health and safety claims made by marketing campaigns do not always align with the latest peer-reviewed scientific evidence. Oftentimes, consumer product claims use language in ways that can be misleading to the average consumer. Review of the human and environmental toxicity profiles of SLS is warranted to elucidate the known risks and benefits of using SLS in household cleaning product formulation.

 

自90年代以來,有著越來越多有關SLS的錯誤資訊,使得人們對這項物質有所誤解,也很害怕使用含有SLS的家用產品(11)。由於輿論,學術論文這種較具有專業度的資訊相對變得弱勢,再加上產品的行銷無法與最新的科學資訊做同步,因此消費性市場的行銷話術難免會誤導大部分的消費者。所以在下方我會依據SLS的毒性特徵(toxicity profile)對目前家用清潔品含有SLS的風險及效益做說明。

 

Review of SLS Toxicity Profiles SLS毒性特徵報告

 

Here, we provide a review of the human and environmental toxicity profiles for SLS in order to address the most common consumer concerns about the ingredient. Unsubstantiated claims regarding the safety of SLS found in print and online media are used to exemplify the origin of several common misconceptions. Each human health and environmental claim is assessed against peer-reviewed scientific evidence for accuracy and validity. This review clearly demonstrates the known risks and benefits of using household cleaning products that contain SLS. Table 1 summarizes the available toxicology data on SLS.

 

我們在本文提供了SLS毒性相關特徵的報告,這是為了要讓大家知道在平面及網路媒體所見相關資訊,現在大眾常對於SLS有著諸多誤解,其實都是源自平面或是網路媒體所提供的、未經證實的資訊。無論跟人體或是環境健康相關的資訊,背後的科學根據其實並不如學界所檢視過的科學根據來得準確。因此結合學術界的專業性,本篇回顧將明確地告知使用含有SLS家用清潔品的效益及風險,並將相關資訊整理在表一

 

Table 1 表一

Toxicity of SLS (CAS# 151–21–3). SLS的毒性(CAS# 151–21–3)

 

 

ACUTE ORAL (RAT)

口服(大鼠)

ACUTE DERMAL (RABBIT)

皮下注射(兔)

ACUTE INHALATION (RAT)

吸入(大鼠)

LOWEST NOAEL (REPEATED DOSE, RAT)

最大容忍劑量最小值(重複投藥, 大鼠)

AQUATIC TOXICITY (96 HRS; FISH)

水中毒性(96小時, 魚類)

Lethal dose or concentration (50%)

半數致死量

1288 mg/kg*

2000–20000 mg/kg*

>3900 mg/m3/1H*

100 mg/kg/day

** (hepatotoxi-city)

(肝中毒)

1–12 mg/L*

 

註解:

* From SLS product manufacturer MSDS (Stepan Company, IL)(5,6)

* 資料來源:SLS產品製造商的化學品安全說明書(史達潘公司, 伊利諾州)(5,6)

 

**From OECD Screening Ingredient Data Set(8)

**源自OECD篩檢成分資料庫(8)

 

Human Toxicity Profile 人體毒性概況

 

Acute toxicity 急毒性

Ocular irritation 眼部刺激
Like most chemicals, SLS can be irritating to the eye when delivered neat as a raw material or at high concentrations. At concentrations <0.1% (w/w), SLS is nonirritating to the eyes of laboratory animals.(1) For this reason, it is imperative for consumer product manufacturers to test finished products for ocular irritation. The U.S. Consumer Product Safety Commission (CPSC;16 C.F.R. §1500) requires consumer product manufacturers to perform irritation tests that appropriately characterize the ocular toxicity of the product.(12) Manufacturers are required to label the product with the appropriate warnings and first aid information according to the mandatory labeling requirements of the CPSC.(12)

 

SLS就像大部分的化學品一樣,無論是利用小劑量還是高濃度的情況下,都會刺激到眼部。在濃度小於0.1%(w/w, 溶質與溶液的重量比值)時,SLS並不會刺激參與實驗的動物眼部(1)。因此對於產品製造商來說,利用成品做眼部刺激測試才是當務之急。美國消費品安全委員會(CPSC;16 C.F.R. §1500)也要求相關廠商做相關的刺激性測試,才能對產品做毒性的分類(12),另外也要求廠商要根據強制性標籤規範中的CPSC.12,在產品標籤上標示出適當的注意事項及急救資訊(12)

 

SLS is cited as causing severe eye damage and blindness.(13) These claims typically point to a study published by Green et al.(14) in the journal Lens and Eye Toxicity Research. The study shows that after the occurrence of physical or chemical damage to the eye, corneal exposure to a high concentration of SLS can result in a slowed healing process. The findings presented by Green et al.(14) do not suggest that ocular exposure to consumer products containing SLS causes blindness or severe damage to the cornea.

 

有些資料指出SLS會嚴重損害眼部,甚至會有失明的狀況,而這一切很可能是源自格林等人在眼睛及晶狀體毒性研究期刊(the journal Lens and Eye Toxicity Research)中發表的一篇研究(14)。研究顯示,眼部在受到物理性或是化學性損傷後,一旦眼角膜接觸到高濃度的SLS,接下來復原的過程會變得緩慢。有發現嗎?這篇由格林所發表的研究(14)並沒有告訴我們,當眼部接觸到含有SLS成分的產品會有失明的症狀或是造成眼角膜嚴重受損的狀況

 

In response to the media attention generated by a company promoting the anti-SLS campaign at the time – Green, the study’s lead author, was interviewed regarding this work. Green stated that the company had misquoted the results and made claims that were not supported by his findings.(15) His legal counsel later issued a letter to the company stating:

 

但目前有越來越多的媒體輿論正因為有個企業推廣不含SLS產品而對它有諸多惡評,正好本次研究有訪問到格林-那篇論文的第一作者(lead author)。他表示,那個企業誤解了他的研究結果,而那些輿論背後的理論跟他在研究中的發現不一致(15)。後來他的法律顧問就寫了一封信回應:

 

…your citation of his work was not simply a misinterpretation, it was plainly wrong. By citing his research in support of erroneous conclusions, you have libeled Dr. Green. In fact, [you have] even attributed quotations to Dr. Green which he has never written or spoken, and which he would not ever write or speak.(15)

 

貴公司並不只是誤解格林先生的論文內容,而是根本就是引用錯誤,而這樣的作法簡直是毀謗了格林博士。簡單來說,貴公司所謂的這些評論背後是根據格林博士,但其實他並沒有這麼說也沒這麼寫,而且他在過去也沒有這麼表示過(15)

 

In this case, the dissemination of misconstrued results not only provided a disservice to the general public but also caused serious repercussions for the scientific researchers.

 

從這方面來看,這種錯誤資訊的傳播不只是有害於公眾而且也會嚴重影響到科學研究領域。

 

A second erroneous ocular health claim made about SLS is its link to cataract formation.(16,17) Claims about SLS causing cataract formation tend to cite a 1987 study in the Journal of Biological Chemistry.(18) This study(18) – along with several others(1921) – uses SLS to model cataract formation experimentally. In a controlled laboratory environment, cataract formation can be induced by immersing the lens of the eye in a concentrated solution of SLS. While concentrated SLS is useful as an experimental irritant, this is not relevant to evaluating human exposure to SLS in household cleaning products. Ocular irritation has been induced in vivo using SLS concentrations equivalent to a rinse-off personal care product containing 20% SLS.(17) However, this was achieved after the eyes of laboratory animals were repeatedly exposed to 0.5 mL of shampoo for 14 days.(17) While SLS is useful in studying the formation and repair of cataracts in laboratory settings, studies of this nature are not appropriate for assessing the risk of human exposure to SLS in cleaning products.

 

第二個錯誤的健康資訊是SLS與罹患白內障有關(16,17)。這個資訊的來源主要是1987年在生物化學期刊(the Journal of Biological Chemistry)所發表的一篇研究。除了這篇研究外,也有其他的研究(1921)使用SLS來試驗是否會造成白內障。在控制實驗室(controlled laboratory)的環境下,研究人員發現當眼球的晶狀體浸於SLS濃縮液時,會引發白內障。儘管如此但並不代表當人體接觸到含有SLS的家用清潔品時,會有罹患白內障的現象。而在活體內使用沖洗型(rinse-off)的個人護理用品時,會讓眼部不適的SLS濃度大約在20%左右(17)。但這是發生在重複在實驗動物的眼部接觸0.5mL洗髮精長達2周後才會發生的狀況(17) 。儘管SLS在實驗環境當中對於白內障的感染和復原的研究有所幫助,但並不能夠由此評估人體在接觸到清潔用品後的風險

 

Furthermore, it should be noted that the anatomy of the eye renders direct exposure of the lens to SLS impossible, as it is deep within the eye protected by the cornea, and therefore, not vulnerable to exposure through typical consumer product usage.(22,23) As such, a causal relationship between SLS in consumer products and cataract formation is not scientifically supported.

 

除此之外,從解剖學來看,因為眼角膜有保護眼球的作用,所以在眼球深處的晶狀體是不可能直接接觸到SLS,也因此在接觸到一般的消費性產品後,眼睛並不容易受損(22,23)。綜上所述,SLS會與白內障的關聯性並沒有任何的科學根據。

 

Dermal irritation 皮膚過敏

Dermal toxicity studies demonstrate that 24-hour exposure to a 1–2% (w/w) solution of SLS can increase the transepidermal water loss of the stratum corneum – the outer most layer of the skin – and cause mild yet reversible skin inflammation.(24,25) Human patch tests (typically a 24-hour exposure) confirm that SLS concentrations >2% are considered irritating to normal skin.(2,26,27) Dermal irritation also tends to increase with SLS concentration and the duration of direct contact.(2) In reality, dermal exposure to SLS in cleaning products is more likely to last a matter of minutes rather than hours.(9)

 

皮膚過敏研究顯示在皮膚接觸濃度1-2%的SLS溶液24小時後,會促進角質層(肌膚最外層)的經皮水分散失,進而造成溫和但可逆的皮膚炎(24,25)。而人體貼布試驗(一般來說為期24小時)證實了當SLS濃度大於2%時可能刺激到一般的肌膚(2,26,27)。除此之外,當SLS濃度及接觸時間越多,肌膚的不適感就會增加(2)。但就常理來看,我們不太可能那麼長的時間接觸到含SLS的清潔用品(9)。

 

Cleaning products that contain SLS have the potential to be dermal irritants if not formulated properly, but products that contain SLS are not necessarily irritating to the skin.(28,29) Proper formulation development includes strategies for mitigating irritation (like adding cosurfactants) and can produce products with SLS that are mild and nonirritating to the skin. Owing to the irritation potential, however, consumer product manufacturers are required to conduct testing to appropriately characterize the dermal toxicity of the product and label the product with the appropriate warnings and first aid information according to the mandatory labeling requirements of the CPSC.(12)

 

儘管那些含有SLS的清潔品可能會刺激肌膚,但SLS並非直接與此有關,而很可能是因為製作過程不當的關係(28,29)。所謂適當的製作過程得包括讓產品緩解刺激的加工流程(像是添加助界面活性劑),這會產出溫和且不對肌膚刺激的產品。儘管理論來說是如此,但根據CPSC強制性標籤規定,消費性產品製造商仍需檢測產品的肌膚毒性,並在標籤上編列適當的警示及急救資訊(12)。

 

Another assertion is that SLS is corrosive to the skin.(11,16) Corrosive chemicals are those that cause irreversible damage or destruction of the skin as a result of direct skin contact. Material safety data sheets for SLS do not categorize this chemical as a corrosive material and do not require any special handling precautions.(68) As such, statements about SLS being corrosive to the skin are inaccurate.

 

另一個消息指稱對肌膚來說,SLS具有腐蝕性(11,16),而一般來說當皮膚在直接接觸到具有腐蝕性的化學物後,會有無法修復的損傷(irreversible damage)。不過,在物質資料表上顯示,SLS並不屬於這類化學物,也不須要任何相關的預防措施(68)。由此來看,所謂SLS能腐蝕肌膚這樣的論述是不恰當的。

 

Oral toxicity 口服毒性

Acute oral toxicity refers to the immediate adverse effects that result from ingesting a substance. The acute oral toxicity of individual ingredients and formulated products is measured in terms of the median lethal dose (LD50), which indicates the quantity by weight (typically in milligrams of substance per kilograms of body weight) required to kill half of the laboratory animals receiving that dose. Ingredients and formulations with an LD50 of ≥5,000 mg/kg are classified as nontoxic.(12) The acute oral toxicity of SLS as a raw material is reported to range from 600 to 1,288 mg/kg (in rats), which indicates that SLS is toxic to rats as a standalone ingredient.(68)

 

所謂急性口服毒性(acute oral toxicity)指的是在攝取一個物質後即刻的副作用,在評估工業原料及配製產品的急性口服毒性時,會利用半數致死量(LD50, 殺死一半實驗體所需的劑量,通常是以劑量(mg)/實驗體體重(kg))作為評定標準。當有一項物質的LD50在5000mg/kg以上時,就代表它是無毒的(12)。我們發現當SLS作為原物料時的急性口服毒性介於600至1288mg/kg之間(實驗體為大鼠),以上述的標準來看,可以說SLS對大鼠來說的確是項有毒物質(68)。

 

The acute oral toxicity of SLS is not disputed, but it is relevant to the overall safety review of SLS. It is important to remember that the toxicity of a formulated consumer product is dictated by the formulation as a whole, not by the toxicity of an individual ingredient. This means that while SLS as a raw material at 100% concentration may have a LD50 of >5,000 mg/kg, formulations that contain diluted or lesser concentrations of SLS are not necessarily toxic and can even be nontoxic. This holds true for the use of SLS in food products as well and explains why SLS is listed on the U.S. Food and Drug Administration (FDA) list of multipurpose additives allowed to be directly and indirectly added to food.(30) Note, too, that every chemical has a toxic dose, and many common foods can be classified as toxic. For example, sodium chloride (table salt) has an LD50 of 3,000 mg/kg, making it moderately toxic by definition.(31)

 

綜上所述,SLS本身的毒性是無庸置疑的,但請記得那是在100%的濃度下測試的結果,也別忘了那些含SLS產品的SLS濃度不可能是100%呀,所以它們的毒性可能更小甚至是無毒的。這也就是為何美國的食藥署允許這項物質添加在食品的原因了(30)。最後要說的是,其實每一項物質都有所謂有毒的劑量,而且許多常見的食品也是。例如,氯化鈉(鹽巴)的LD50為3000mg/kg,從前文的標準來看,它是屬於毒性中等的物質(31)。

 

Chronic toxicity 慢性毒性試驗

Carcinogenicity 致癌性;誘癌性

The most egregious claim by far is that SLS is carcinogenic.(16,32) The origin of this claim is uncertain, but it is likely to have derived from multiple misinterpretations of the scientific literature. There is no scientific evidence supporting that SLS is a carcinogen.(33,34) SLS is not listed as a carcinogen by the International Agency for Research on Cancer (IARC); U.S. National Toxicology Program; California Proposition 65 list of carcinogens; U.S. Environmental Protection Agency; and the European Union. In 1998, the American Cancer Society (ACS) published an article attempting to correct the public’s misconception of SLS.(32) Regardless, false claims about SLS proliferated throughout the digital media, causing consumers to develop significant concerns about SLS in household cleaning products.

 

到目前為止,最讓我覺得匪以所思的是,竟然有很多人說SLS是致癌物(16,32)。儘管不太確定這項消息最早的來源,只知道很可能是來自於科學文獻的諸多誤解,但目前沒有任何科學證據支持這項說法(33,34),而且國際癌症研究機構(IARC)、美國國家毒理學計劃、加州65號提案(1986 年安全飲用水和有毒物質強制法案)、美國國家環境寶物局及歐盟並沒有將SLS列入致癌物中。除此之外,美國癌症協會(the American Cancer Society, ACS)早在1998年就發表了一篇釐清SLS的文章(32)。無論如何,大眾的確受到了媒體的影響,對於添加SLS的家用清潔產品仍有疑慮。

 

The perception that SLS is carcinogenic is often based on studies that use the ingredient to evaluate the carcinogenicity of other agents. An article written by Birt et al.(36) is commonly cited as supporting the carcinogenicity claim for SLS. However, this is another example of public misinterpretation and the resulting dissemination of inaccurate information. In the study by Birt et al.(35), SLS was used as a vehicle to process the agent being tested. No evidence supporting the carcinogenic effect of SLS was reported. It is apparent that the common use of SLS as a solubilizing agent in toxicology studies has led to the public’s confusion around the chronic toxicity of SLS.

 

與前文相同,SLS是致癌物的說法通常是來自於那些直接使用這項物質來評估SLS致癌性的研究。其中最常被拿來引用的是一篇由Birt等人發表的研究,但這又是另一個大眾對於科學文獻的誤解。在這篇研究中,SLS只是用於處理試驗中介質的一項載體,並沒有任何支持SLS有致癌性的證據。很明顯的,SLS只是常用來作為毒性試驗的助溶劑,卻因為最後的實驗結果,導致大眾對於SLS會有這樣的誤解。

 

Other claims denouncing SLS as a carcinogen point to a chemical reaction between SLS and formaldehyde that creates nitrosamines as a by-product.(32) However, it is not possible for SLS and formaldehyde to react and form a nitrosamine. Nitrosamines contain two nitrogen atoms, but neither SLS nor formaldehyde contain nitrogen atoms. Therefore, the two cannot react to form a nitrogen-containing nitrosamine. Although nitrosamines have been associated with several types of cancer and many are classified by IARC as known, possible, or probable carcinogens depending on the chemical species,(34) they cannot be associated with the presence and use of SLS.

 

除此之外,也有人因為SLS和甲醛的化學反應會產生亞硝胺的關係,所以認為它是一種致癌物質(32)。但SLS和甲醛是不可能會有化學反應,更別說會產生亞硝胺了(因為亞硝胺的化學結構有SLS和甲醛所沒有的氮原子)。綜上所述,IARC等組織的確將亞硝胺列為致癌物質(34),但這跟SLS並沒有任何關係。

 

Another carcinogenic by-product, 1,4-dioxane, is falsely associated with SLS.(32) 1,4-dioxane is categorized as possibly carcinogenic to humans by IARC,(34) and the potential for some surfactants – like sodium laureth sulfate (also called sodium lauryl ether sulfate or SLES) – to be contaminated with 1,4-dioxane during the ethoxylation process is well established.(36) Barring contamination by manufacturing equipment, surfactants that are not ethoxylated, such as SLS, do not share the same risk of 1,4-dioxane contamination. It is important to note, however, that potential for cross-contamination during manufacturing exists. Manufacturers of SLS and products containing SLS can perform chemical analyses to confirm if there are detectable levels of 1,4-dioxane in the SLS ingredient or formulated consumer product.

 

除了亞硝胺外,另一項致癌物-1,4-二噁烷也被誤認跟SLS有關(32),的確IARC將1,4-二噁烷歸類為致癌物質,而且有些界面活性劑(像是十二烷基聚氧乙醚硫酸鈉/SLES)可能在乙氧基化的過程中,可能會受到這項化學物質的汙染(36)。不過換個角度想,如果生產設備並沒有汙染的疑慮,那麼就不會有相同的狀況。所以說如果SLS及相關產品的生產商能夠事先預防並做化驗,就能避免這樣的狀況了。

 

Organ toxicity 器官系統毒性

It is often claimed that SLS absorbs into the blood stream, builds up in the heart, liver, lungs and brain, and causes damage.(13,16) Claims of this nature often cite the Cosmetic Ingredient Review (CIR) Final Report on the safety of SLS, which contains an extensive review of the absorption and excretion of SLS in humans and animals.(1) However, the CIR concludes that while SLS can be absorbed through the skin when applied directly, the majority of the material remains in or on the skin surface. SLS that is absorbed into the bloodstream is quickly metabolized by the liver into more water-soluble metabolites that are rapidly excreted through the urine, feces, and sometimes expired breath.(1,22,23,37) There is no evidence in the CIR report or in the scientific literature at large that supports the accumulation of SLS in vital organs and associates it to systemic toxicity or vital organ damage.(22,23,33) As such, accusations that SLS will bioaccumulate in humans and cause organ damage are inaccurate.

 

常聽到有人說血液會吸收SLS後,會累積在心臟、肝臟、肺部及腦部,最後會造成損害(13,16)。這種說法是來自化妝品成分評論(Cosmetic Ingredient Review, CIR)中對於SLS的安全性評估,其中包括了在人體及動物吸收及排泄SLS的狀況(1)。但CIR的結論是當SLS直接敷在皮膚上時儘管能吸收SLS,但大部分的SLS仍留在表面。而肝臟能直接代謝在血液中吸收的SLS,並轉換成可溶於水的代泄物,接著透過尿液、糞便,有時候甚至是呼吸將其排出(1,22,23,37) 。在CIR或是其他的科學文獻中,並沒有任何證據直接支持SLS會累積在重要的器官並與系統毒性或是重要器官的損害有關(22,23,33)。綜上所述,所謂SLS對人體有生物累積效果並造成器官的損害的說法有誤。

 

Dermatological effects 皮膚病學

Hair loss 毛髮脫落

The CIR report(1) is also cited as supporting the claim that SLS can cause hair loss and baldness.(13,16,32) The CIR report states as follows:

 

SLS會造成毛髮脫落甚至會禿頭這樣的說法(13,16,32)是來自CIR報告(1)。以下是CIR報告中提到的相關內容:

 

Autoradiographic studies of rat skin treated with radiolabeled Sodium Lauryl Sulfate found heavy deposition of the detergent on the skin surface and in the hair follicles; damage to the hair follicle could result from such deposition.

 

在大鼠皮膚上使用放射自顯影的SLS這項研究中發現,皮膚表面及頭髮毛囊上會留下高濃度的沉積物,進而造成毛髮的損傷。

 

The report goes on to say that high concentrations of SLS may affect the hair, but no evidence is presented to show that SLS exposure causes hair loss. Rather, the report recommends that cosmetic products applied to the skin not contain concentrations of SLS >1% due to its potential to deposit on hair follicles.(1,2) In addition, the report states that additional research would be required to elucidate the true effects of the deposition. As of 2015, no scientific evidence has been produced to suggest that dermal exposure to SLS causes hair loss.

 

但這樣的研究結果是建立在高濃度SLS的情況,且並沒有任何證據顯示,頭皮接觸到SLS後會有掉髮的現象。除此之外,考量到SLS可能會有損害肌膚,市面用於肌膚上的化妝品中所含這項化學品濃度並不會超過1%(1,2)。除此之外,這項報告指出,需要有更多的研究來證實SLS會造成掉髮這樣的說法。

 

A study published in 1998 by the European Journal of Dermatology is also cited as supporting claims that SLS causes hair loss.(38) This study investigates the effects of oxidative stress on skin irritation and uses SLS as an experimental irritant. There is no discussion of hair loss. As in the CIR report, the researchers of this study(38) identified the deposition of SLS on the root sheath of the hair follicle but did not draw conclusions about the effects of this deposition on the hair. The study(38) in no way suggests that SLS is responsible for, or contributes to, chronic hair loss. In general, no data have been generated to elucidate the long-term effects of SLS deposition on hair follicles, but based on the widespread and long-term use of SLS in hair care products, such an effect is highly unlikely. Overall, claims that associate the use of SLS-containing products with hair loss are not scientifically supported.

 

SLS會造成毛髮脫落的另一個消息來源是源自於1988年的歐洲皮膚病學周刊(the European Journal of Dermatology)裡的一篇研究(38)。這項研究針對肌膚刺激的氧化壓力效果進行調查,並用SLS作為實驗中的刺激物,但其中並沒有任何跟毛髮脫落有關的內容。而在CIR報告裡,這項研究的學者只是檢測殘留在頭髮毛囊根鞘上的SLS而已,並沒有針對殘留在毛髮的SLS的影響得出結論。因此我們無法從這項研究去推測SLS跟慢性的毛髮脫落有關,或者說是會造成這樣的現象。目前也沒有任何針對SLS對頭髮毛囊的長期影響的資料,但就目前大家廣泛並長時間使用含有SLS的頭髮護理產品後,其實並不太可能掉毛髮。整體來說,所謂含SLS的產品的使用會跟毛髮脫落有關並沒有任何科學根據支持著。

 

Sensitization 敏感度分析

Another unsubstantiated claim about SLS is that it can cause severe dermal sensitization.(13,16) A sensitizer is a substance that causes hypersensitivity through an allergic or photodynamic process, which becomes evident on reapplication of the same substance on the skin. There is no scientific evidence to support that SLS has sensitization potential. SLS is not included on any lists of known or suspected sensitizers.(33) Therefore, stating that SLS is a sensitizer is inaccurate.

 

另一個毫無科學根據的說法指稱,SLS會造成嚴重的皮膚過敏(13,16)。那麼在科學上所謂敏化劑是指在光動力療法或是過敏的過程,產生超敏反應的一項物質,而這也是測試人體過敏反應的一項證據。但從這樣的方法來看,並沒有任何相關證據支持SLS會造成過敏這樣的說法,而且在敏化劑的資料裡也沒看到它(33)。因此,所謂SLS是致敏物質說法是不正確的。

 

Other chronic toxicities 其他慢性毒性試驗

To a lesser extent, claims about SLS causing chronic adverse health effects – such as mutagenicity, reproductive and development toxicity, neurotoxicity, and endocrine disruption – have been made without adequate substantiation.(16) Therefore, it is worth mentioning that SLS has no known chronic health effects. According to the National Library of Medicine’s TOXNET® database, SLS is not classified as a known or suspected mutagen, reproductive or developmental toxicant, neurotoxicant, or endocrine disruptor.(33)

 

有消息指稱,SLS會對身體的健康有長期負面的影響,可能會有基因變異毒性(mutagenicity toxicity )、生殖毒性(reproductive toxicity)、發育毒性(development toxicity)、神經毒性(neurotoxicity, 神經錯亂)以及干擾內分泌系統(endocrine disruption)等現象,但這樣的說法並沒有任何的科學根據(16)。因此可以說其實目前還無法確定SLS會對人體有何長期健康方面的影響。而且根據美國國家醫學圖書館的毒理學數據網路資料庫中的資料顯示,SLS並沒有歸列為基因變異、生殖或發育毒素、神經毒物或是內分泌干擾素裡(33)。

 

Environmental Toxicity Profile 環境毒性特徵

Use and disposal of cleaning products release SLS into the environment via household wastewater systems. Therefore, the environmental toxicity profile is an important consideration when evaluating the risks and benefits of using SLS in household cleaning product formulation. Although the environmental toxicity of SLS does not appear to be a point of debate in online communications, a concise review is included to demonstrate the end-use effect of this ingredient.

 

在使用清潔用品後,會透過家用的廢水系統將SLS排放到環境當中。因此,就需要利用環境毒性特徵,進而評估使用含有SLS的家用清潔用品對環境的好壞。儘管我們目前在輿論中未曾見過相關的評論,但針對本項研究,我們簡單整理出相關的資訊。

 

Aquatic toxicity 水生毒性

Aquatic toxicity refers to the short-term adverse effects that result from the exposure of aquatic life to a chemical or formulation. This type of toxicity is measured in terms of the median lethal concentration (LC50), which indicates the quantity by volume (typically reported as milligrams of substance per liter of water) required to kill half of the experimental population exposed to that dose. Ingredients or formulations with an LC50 of ≥100 mg/L are classified as nontoxic to aquatic life.(39)

 

所謂的水生毒性是指,水生動物在接觸到化學品或是延伸產品後的短期副作用,通常會使用半數致死濃度(the median lethal concentration, LC50, 單位為mg(化學品)/公升(水))作為計算標準,意即能殺死半數以上實驗體的濃度。如果說有一項化學品的LC50大於100 mg/L,那代表對於水生生物來說,這是無毒的(39)。

 

As a raw material, the LC50 for SLS is reported between 1 and 13.9 mg/L after 96 hours, categorizing it as moderately toxic to aquatic life.(68),(4044) Like acute oral toxicity, aquatic toxicity values for individual ingredients do not directly correspond with the toxicity of formulated consumer products. This means that while SLS is moderately toxic to aquatic life in its raw material form, product formulations that contain dilutions of SLS are not necessarily moderately toxic and, in fact, can be nontoxic to aquatic life. However, the toxicity of SLS depends largely on the marine species, water hardness, and water temperature.(41,43,44)

 

在經過96小時後,我們發現SLS的LC50在1-13.9mg/L之間,可說對於水生動物來說,它是中等毒性的化學物質(68),(4044)。但就像是急性口服毒性那個段落所提到的,這樣的結果並不能反映在消費性產品上,簡單來說,這樣的資料是把SLS當作原物料來測試,但消費性產品除了含有SLS外,也包含其他成分,所以有可能是無毒的,除此之外,SLS的毒性很大一部份其實受到了水生動物的品種、水的硬度以及水溫等的影響。(41,43,44)

 

By the time cleaning product ingredients reach natural waters, they are mostly degraded. Ecotoxicity studies have determined that a surfactant concentration of 0.5 mg/L of natural water would be essentially nontoxic to fish and other aquatic life under most conditions.(42) It is suggested, however, that chronic toxicity of anionic surfactants occurs at concentrations as low as 0.1 mg/L.(40)

 

一般來說,當清潔用品接觸到自然水時,原料大部分都會被降解。在環境毒性研究也顯示,進到自然水後,SLS的濃度大約為0.5mg/L,因此對魚類或是其他水生生物來說基本上是無毒的(42);不過當陰離子介面活性劑的濃度在0.1 mg/L時,可能會對水生生物有慢性毒性的影響(40)

 

Biodegradability 生物降解性/生物可分解性

The ability of a chemical to decompose into simple, nontoxic components under ambient environmental conditions within a short period of time (typically 96 hours) means that it is biodegradable. SLS is readily biodegradable under aerobic and anaerobic conditions and, therefore, does not persist in the environment.(8,37,45) The biodegradation of SLS occurs via hydrolytic cleavage of the sulfate ester bond leaving inorganic sulfate and fatty alcohol. These fatty alcohols undergo oxidation to produce fatty acids, which are degraded by β-oxidation and fully mineralized and incorporated into the biomass.(45) Thus, the decomposed by-products of SLS are benign to the environment.

 

如果說今天有一個化學物質在周遭環境下,於短時間內(一般來說是96小時)分解為結構簡單、無毒的成分時,就代表它具有生物降解的特性。而無論在有氧及厭氧的環境下,很容易就能將SLS生物降解,因此並不會有殘留環境的疑慮(8,37,45)。在生物降解的過程中,SLS會水解分裂,將硫酸酯化學鍵與無機的硫酸根及脂肪醇分離。接著脂肪醇氧化後會產生脂肪酸,然後將脂肪酸氧化分解並完全礦化成生物質(biomass)(45)。簡單來說,SLS的生物降解對環境是有益的。

 

Biobased content  生物基成分

The biobased content of an ingredient is a primary criterion for formulating sustainable consumer products. The biobased content of an ingredient or formula is the percentage of carbon molecules in the chemical or formula that is derived from a renewable source – such as coconut or palm kernel oil. The biobased content of plant-derived SLS is 100%, which indicates that all of the carbon in the molecule is derived from a plant source rather than a nonrenewable, petroleum source. By comparison, SLES – a surfactant commonly used in household cleaning product formulations – is an ethoxylated surfactant containing carbon molecules derived from petroleum. SLES ethoxylated with petrochemicals has a biobased content of ∼76%. From a sustainability and environmental health perspective, sourcing surfactants such as plant-derived SLS avoids incurring the additional environmental and human health impacts caused by the extraction of petroleum and the production of petrochemicals.

 

一項產品所含的生物基成分比例是評斷產品是否符合永續性的主要標準,那麼在它的成分比例方面,得去看成分中有多少的碳分子是來自可再生來源,例如椰子油或是棕櫚仁油。以植物提取的SLS來說,它的生物基含量為100%,也就代表成份裡所有的碳分子是來植物而非不可再生的石油。而另一方面,同樣屬於界面活性劑、常用在調製家用清潔產品的SLES,就是屬於後者,它的生物基比例為76%。從生態永續性及環境健康的層面來看,使用像是植物提取的SLS這樣界面活性劑,較能避免對環境及人體健康有負面的影響。

 

Conclusion 結論

The review of SLS toxicity profiles confirms that SLS is an acceptable surfactant for use in household cleaning product formulations from toxicological and sustainability perspectives. Years of anti-SLS campaigns have led to consumer concerns and confusion regarding the safety of SLS. Yet, the primary concern – that SLS has potential for being irritating to the eyes and skin – can be easily addressed by proper formula development and appropriate irritation testing performed by the product manufacturers. SLS is considered a sustainable material because of its 100% biobased content, biodegradability, and low potential to bioaccumulation. Toxicological data support that SLS is safe for use in cleaning products when formulated to minimize its irritancy potential. It is concluded that the use of SLS in cleaning product formulations does not introduce unnecessary risk to consumers or the environment because of the presence of the ingredient, and, if properly formulated and qualified, does not pose danger to human health and safety. Therefore, the perception that SLS is a threat to human health is not scientifically supported, and claims made to the contrary should be regarded as false and misleading.

 

從SLS毒性特徵的文獻回顧中,可以知道無論是對於生態環境還是人體健康方面,作為家用清潔品的介面活性劑是安全無虞的。這證明了多年來對於SLS的負面輿論,真的是誤導了消費者。首先,SLS的確有刺激眼睛及肌膚的風險,但只要製造方有適當的加工過程以及刺激性試驗,就可以減少這樣的風險。再者,由於SLS本身是100%提取自植物的,同時兼具生物降解性及低生物累積風險,可以說它是一項永續性的物質。除此之外,對於含SLS的清潔用品的使用是否是安全無虞的,毒物學的相關資料給予正面的支持。綜上所述,在調配清潔用品的過程中添加SLS時,如果有適當的加工流程及良好的品質控管,並不會對環境及人體有任何負面影響,因此那些SLS界面活性劑相關的負面輿論及說法背後並沒有任何的科學根據支持。

 

 

原文翻譯自Human and Environmental Toxicity of Sodium Lauryl Sulfate (SLS): Evidence for Safe Use in Household Cleaning Products一文

 
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