Shampoo & Conditioner

Written By Anna Dimling

Issue

Until more modern science and industrialization, people maintained their hair using various available natural ingredients, animal, vegetable, and minerals. In 3000 BC, soap was made from animal fats boiled with ashes and ancient Egyptians (around 2000 BC) used citrus juice and water to shampoo and animal fats or plant oils to condition their hair. Also the Indus Valley Civilization (in modern day Pakistan and Indian from 3300 BC to 1300 BC) boiled tree ingredients (Sapindus, Indian Gooseberry or Amla) and strained them into an extract for cleansing and improving hair growth and shine. In 1927, the first version of liquid shampoo was invented in Germany and the manufacturing process and ingredients have changed significantly over the last 100 years. Shampoos have evolved to be designed for certain features and functions, for example some ingredient’s function is to provide hair with moisture (emollients), create shiny appearance in shampoo (pearlescent), or add volume (humectants); while other ingredients are to ensure liquids blend (emulsifiers) or increase shelf-life (preservatives). While most of these ingredients do not have any concern, there are some ingredients that are harmful or sensitizing chemicals like formaldehyde-releasers, fragrances, parabens, and phthalates.

Solutions

There are different ways to avoid sensitizing or more harmful chemicals when it comes to shampoo products. Some of the major options to consider are…

  • Buy products with less ingredients and look at labels.

    • Identify any certifications (see “Certification” section below)

    • Use app or website to determine hazard level of the shampoo product (see “Finding Safe Products” below).

    • Look at label for chemicals to avoid. While this can be a good method, I would not go overboard with this since it can be overwhelming. Focusing on certifications, trusted brands, or looking up on the websites are probably easier methods.

  • Shampoo and condition your hair less or go along with the “No Poo” movement.

    • Washing your hair too often can have drying and affect your natural hair oils and scalp. This will reduce your exposure to any harmful ingredients in shampoo and make your hair healthier in the process.

    • Some people never use shampoo and opt for apple cider vinegar or other natural alternatives to wash clear hair of natural oils when they build up.

    • Another way to not wash hair as often is to “oil train” your hair so that your scalp does not produce as much oil. Dry shampoo and washing hair often makes you scalp produce more of the natural oils that are stripped away or absorbed by the dry shampoo. There are a lot of resources online for this, but here is a good resource.

  • Experiment with local shampoo products from a trusted source.

    • It is always great to support your local community and can be fun to experiment with different products, shampoo bars or other more natural conditioners. Check your local flea or farmers market.

  • Try shampoo bars.

    • These tend to have more natural ingredients and are more eco-friendly due to the sustainable packaging and lower weight for shipping (no water).

  • Avoid aerosol dry shampoo products (and other aerosol personal care products).

    • The concern here is for a benzene impurity. Buy or make your own powdered dry shampoo.

As with all consumer products the responsibility should not be on the consumers. More regulations and/or lawsuits should require companies to…

  • Be more transparent about the risks of certain ingredients, whether its removing the ingredient, providing clear labeling, and/or identifying potential hazards on the shampoo product.

  • Reimburse consumers for health conditions caused by the shampoo product from lawsuit settlements.

  • Research and investigate non-toxic ingredients that can replace other more harmful ingredients (e.g., formaldehyde-releasing preservatives).

  • Require third party testing for formaldehyde in certain products, especially hair straightening products.

Bottom Line

Choosing shampoos and conditioners with better ingredients can make a difference in your scalp, hair, hormones, and overall health. As stated below, many shampoos can cause scalp conditions and even more harmful effects over time. However, you can avoid these by avoiding shampoos with:

  • Carcinogens like formaldehyde, Cocamide DEA, and potentially contaminated petroleum-based substances.

  • Formaldehyde-releasing agents (see list and description below).

  • Endocrine or hormone disrupting ingredients (e.g., Pthalates, Parabens, Lilial).

  • Fragrances (note that essential oils are generally ok unless you are sensitive to them).

  • Drying ingredients like sulfates and alcohols.

  • Other potential skin sensitizing ingredients like Harsh foaming agents (SLS) and silicones.

Details

Shampoo and Conditioner Background

The global shampoo market size in 2022 was valued at $32.8 billion dollars and project to grow about $18 billon dollars by 2030 (FMI, 2024). The main reasons why shampoo is used is to remove excess oil, dirt, and odors from the scalp, and conditioners are meant to keep hair moisturized and strong. There are many differing opinions on which shampoo brand or method is best for healthy hair and scalp; however, like many things cleansing your hair is a balance. Shampoos and conditioners can vary widely however, they generally contain over 50% water (as the solvent) and the following functional components (percentages are averages based on a study) (Punyoyai C. et al., 2018):

Shampoo pie chart identifying ingredients with health and/or environmental concerns and better alternatives for each functional component.

  • Surfactant (25%) - This component’s main function is to cleanse dirt and oil from the hair and scalp, as well as create a foam or lather. Sometimes called detergents, certain surfactants can be harsh on the scalp (sulfates) or be more harmful chemicals (like PFAS), which are still sometimes added, but mostly getting phased out of shampoo formulations. On the flip side, there are several mild surfactants derived from coconut oil, including Cocamidopropyl Betaine and Sodium Cocoyl Isethionate, with no known hazards or concerns.

  • Thickener (7.5%) - Improve the viscosity (or thickness) of the shampoo to make it more manageable and ensure ingredients stay evenly distributed. Some more harmful ingredients (Polyethylene Glycol and Cocomide DEA) have been linked to cancer due to contamination concerns or listed on California’s Proposition 65 (OEHA, 2018). Some less harmful alternatives for thickeners include salt and xanthum gum.

  • Other Agents (6%) - There are many other functional agents added to shampoos, specifically emulsifiers (blend ingredients together) and solubilizers (help dissolve ingredients). Isopropyl alcohol is used a a solubilizer, but can be more drying on the hair and scalp (like other short-chain alcohols) than something like cetearyl alcohol (long-chain alcohol). Siloxanes are common emulsifiers that persist and accumulate in the environment, as well as are toxic to many aquatic organisms. A better environmentally friendly emulsifier is coco glucoside, made from coconut oil.

  • Pearlescent (5%) - Mostly added for the visual appeal of the shampoo, to make it have a shimmering, pearly appearance. The most common pearlescent in shampoos, glycol distrearate, does have health concerns. However, another shampoo pearlescent, Sodium C12-13 Pareth Sulfate, can be a scalp irritant and may contain 1,4-Dioxane (a carcinogen) as an impurity.

  • Emollient (2.5%) - Added to moisturize the hair and scalp. Petroleum-derived mineral oil is commonly used in shampoos, but may have contaminants like Polycyclic Aromatic Hydrocarbons (PAHs) which are known to be carcinogenic. A natural, sustainable emollient alternative is lanolin, a waxy substance from the wool of sheep.

  • Humectant (1.5%) - These help attract and retain moisture in the hair and scalp. Similar to mineral oil, propylene glycol is a petroleum-derived ingredient with contamination concerns from more harmful chemicals such as ethylene glycol and 1,4-Dioxane due to poor manufacturing practices.

  • Preservative (0.5%) - Exend the shelf life of shampoos and conditioners by preventing the formation of harmful microorganisms like bacteria, fungi, and mold. Formaldehyde, a known carcinogen, is an excellent perservative. Therefore, a lot of shampoos use ingredients known as formaldehyde-releasers, which will be banned in the European Union (EU) in 2026. U.S. Regulators (Food and Drug Administration and Cosmetic Ingredient Review) state that the amount of formaldehyde released is small enough not cause a concern. Note that there are no federal limits for formaldehyde or formaldehyde-releasers in cosmetics. Triclosan is also widely used antimicrobial agent that has be shown to have endocrine-disrupting properties including thyroid regulation and estrogen activity. Alternatively, there are natural, non-harmful preservatives like rosemary extract, Vitamin E, and grapeseed oil.

  • Perfuming Agent (0.5%) - Added to either mask the bad smell of the shampoo or add nice smell to the shampoo. Synthetic fragrance ingredients, like parabens and phthalates, can cause hormone disruption. It is better to look for shampoos that are “fragrance-free” or scented with natural occurring scents, like essential oils and plant extracts.

  • Colorant (0.5%) - Ingredients are added to change the color of shampoo. Synthetic dyes, like FD&C Blue 1 and Red 40, can contain harmful impurities, such as heavy metals, aromatic amines, and other manufacturing by-products. Less harmful colorants include natural dyes like henna, beetroot, or minerals (e.g., mica, bentonite clay).

Harmful Chemicals Found in Some Shampoos

Carcinogens - Chemical substances that are known to cause various cancers.

  • Formaldehyde - Recognized as a carcinogen by many different government agencies all over the world. Used as a preservative in shampoo in US, and banned in EU for all cosmetic products.

  • Cocamide DEA and MEA - Common thickener used in shampoos and classified as potential carcinogens under California’s Proposition 65.

  • Benzene - Many spray dry shampoos have been found to contain benzene as a contaminant (not listed in ingredients), see more in the lawsuits section below.

  • Perfluoro and polyalkyl Substances (PFAS) - Many products are contaminated with PFAS because they can enter products through water containing PFAS, bottles with PFAS coatings, and many other routes. Governments are just starting to understand the scope of PFAS in products, environment, and the human population.

Contamination Concern - Sometimes certain ingredients can contain other chemicals as impurities or contamination, which are more harmful than the ingredient listed on the label.

  • Petroleum-based substances - Chemicals that are produced from petroleum can have harmful impurities, including polycyclic aromatic hydrocarbons (PAHs), that can cause cancer. Some commons ones include:

    • Mineral Oil - Added to help condition or detangle hair. Same oil used for paraffin wax.

    • Coal Tar - Added as an anti-dandruff ingredient in shampoos.

    • PEG (Polyethylene Glycol) - Added as a thickener.

    • PG (Propylene Glycol) - Added as an humectant.

    • DEA (Diethanolamine) - Added as an emulsifier to combine oil and water ingredients.

  • 1,4-Dioxane - This would not be listed on labels, but may be created in the formulation or as a contaminant in chemicals like sodium laureth sulfate and PEG or chemicals with "Ceteareth” and "Oleth” in the name.

  • Dyes - Certain colorant ingredients are added to shampoos to change the color and some of the dyes themselves may be harmful or they also may contain harmful contaminants. For instance, some dyes with ‘lake’ indicate they are produced with metal salts, such as aluminum, calcium, barium, and others. Also many dyes are synthetically produced from coal tar or petroleum.

Formaldehyde-releasing substances - While these substances are different compounds than formaldehyde, they produce small amounts of formaldehyde gradually over time when they degrade, react with the water, or are in high temperature environments. These substances are added to shampoos and conditioners as a preservative, since formaldehyde prevents the growth of bacteria and mold. Here is a list of common formaldehyde-releasing substances added to shampoos and conditioners:

  • DMDM Hydantoin

  • Quarternium-15

  • Imidazolidinyl urea

  • Ureadiazolidinyl urea

  • Polyoxymethylene urea

  • Sodium hydroxymethylglycinate

Benzene-Forming Substances - Benzene is a known carcinogen and can form if certain ingredients are in shampoo. For instance, Vitamin C (aka Ascorbic Acid) mixed with sodium benzoate (common shampoo preservative) can produce small amounts of benzene. This chemical reaction was mentioned in a lawsuit against a specific shampoo brand, however, these two ingredients are likely in various brands.

Endocrine Disrupter and/or Reproductive Toxicity - Chemical substances that affect hormones and fertility.

  • Tricoslan - An antibacterial and antifungal agent used as preservative that has been proven to be an endocrine disrupter.

  • Lilial - A synthetic scent ingredient that was classified as “reprotoxic” and banned in the EU and Northern Ireland since March 1, 2022, but remains unregulated in the U.S. (SCCS, 2019).

  • Phthalates - Synthetic fragrances usually contain phthalates that are released into the air when burning candles. These chemicals are known to increase allergies or asthma and affect hormone levels.

  • Parabens -These synthetic chemicals are added to synthetic fragrances, waxes, or dyes as a preservative and are also known endocrine-disrupting chemicals, or affect human hormones.

  • Siloxanes - These were found to be toxic, persistent, and bioaccumulative to aquatic organisms when released into the environment (Government of Canada, 2023). There are also some studies that link these chemicals to endocrine disruption as well.

Sensitizers and Other Non-Desirable Ingredients

There are a large variety of ingredients in shampoos and conditioners that can cause allergic reactions in some people. This could cause dermatitis of the scalp or even face, neck, eye, and back.

  • Fragrances - Typically a mixture of various components including aromatic compounds (natural or man-made), carrier oils (e.g., diethyl phthalate, dipropylene glycol), and other ingredients. Can contain various hazards substances and cause allergic reactions, respiratory irritation, and other adverse health reactions.

  • Silicones (ingredients ending in ‘-cone’) - Silicones are safe in terms of health but some believe they are not “healthy” since they can build-up in your hair and scalp. Essentially it coats the hair and repels water so it does not easily wash away, which could cause itching, flaking, and inflammation on the scalp.

  • Sulfates - Added to form foamy texture in shampoo, but can be strip too much oil and dirt from hair causing it to lose it’s natural moisture and oils. This can leave the scalp dry and prone to irritation. Sodium Lauryl Sulfate (SLS) has was found to cause an irritant reaction to 42% of 1,600 participants of a German Study (Geier et. al, 2003).

  • Alcohol - A very common ingredient in shampoos which can have a drying effect on your hair causing it to be brittle and break.

  • Linalool and Limonene - Natural occurring substances found in many flowers and spice plants (linalool) or citrus fruits (limonene), but can cause skin sensitivity in some individuals.

  • Methylchloroisothiazolinone and methylisothiazolinone (MCI/MI) - Preservatives that are used in many personal care products can cause contact dermititis.

What products contain hazardous chemicals?

In January 1998, the Danish Product Register Database (PROBAS) identified 82,900 products with formaldehyde or formaldehyde releasers in them, and 2,255 of those products were shampoos or other hair care products (Flyvholm, 2000). In some cases harmful chemicals are ingredients listed on the product label, but sometimes they are not listed. Typically these products contain harmful chemicals as an impurity (chemical not intended in final ingredient/product which was not removed during the chemical processing) that are not listed on the label. An example of this is benzene being found in dry shampoo and other aerosol products (see more information about this down below). The best way to identify which shampoo and conditioner products contain harmful chemicals is to look for trusted certifications or the app/websites listed below.

Certifications

Labels

Reading labels can be exhausting when shampoos contain up to 30 ingredients of words you have never heard before. Here are some rules of thumb when looking at labels:

  • Choose shampoos with fewer ingredients

  • Look for certifications like the ones listed above (i.e., EWG Verified®, NSF Certified®)

  • Avoid purchasing shampoo products online from un-trustworthy sources that may be selling counterfeit products (e.g., imposter sellers on Amazon)

  • Product should state “Sulfate-Free”, “Paraben-Free”, “Fragrance-Free”, and “Phthalate-Free”

  • Find potentially harmful or undesirable ingredients without knowing all chemicals:

    • Silicones - Names that end with “-cone” (e.g., dimethicone)

    • Parabens - Names with “paraben” (e.g., methylparaben, propylparaben)

    • Phthalates - Look for “Phthalate” (e.g., Dibutyl Phthalate)

Finding Safe Products

Note that these tools are should not be taken as the ultimate truth on whether a product is safe or right for you. However, each provides valuable information and guidance on how to steer away from more harmful shampoos or conditioners.

  • EWG Product Search - EWG ranks personal care products with a score from the lowest hazard (1) to highest hazard (10) based on ingredients and data availability levels (no data to robust). Typically, if a product is EWG verified® (see above) or a lower hazard score (1 through 6) the product does not have as many health concerns. The database also provides the function and health concerns for each ingredient.

  • INCIDecoder - A website that allows you to search shampoo and other personal care products to see a list of the ingredients, what each ingredient does, and whether it has any hazards.

  • Skinsafe - A website that provides the scores (100 being the best or most “skin safe”) for various personal care products, including hair care. The website also indicates any common allergens that may be present in products.

  • Think Dirty - An app that labels each ingredient in personal care product as either clean, half and half, dirty, and not rated. The show the amount of ingredients in each of these categories along with user ratings and reviews. There is quite a bit of the app you have to pay to view.

  • Yuka - An app where you can scan or search for products and they rank them out of 100 based on the ingredients.

Chemical Hair Straighteners

Some hair straighteners can contain as much as 10% formaldehyde. One study found that of the 7 Brazilian Keratin Treatment products tested, 6 contained formaldehyde levels ranging from 0.96% to 1.4%. These levels are 5 times higher than the recommended level (0.2%) by the US Cosmetic Ingredient Review Expert Panel and 5 of the 7 products were listed as “formaldehyde-free” (Maneli, 2014). There have been several lawsuits to address this issue, however, consumers should use caution and research their chemical hair straightener brand before using.

Progress

Regulations

While personal care products are much less regulated than other consumer products, there have been many strides especially since 2020 in the United States.

Lawsuits

The major lawsuits that we found had to do with hair straightening products, however, there have been some lawsuits having to do with labeling and transparency with certain harmful ingredients

  • Brazilian Blowout Lawsuit - In 2012, Brazilian Blowout, a popular hair straightening product, settled a class-action lawsuit in the United States. The product was found to contain high levels of formaldehyde, despite being labeled as formaldehyde-free. Stylists and customers reported health problems like eye and respiratory irritation due to the formaldehyde gas released during the treatment. The company eventually settled the lawsuit for $4.5 million as well as agreeing to other testing, transparency, and oversight (OAG CA, 2012).

  • Keratin Complex Smoothing Therapy Lawsuit - In 2013, a California woman filed a lawsuit against Keratin Complex, claiming that their hair-smoothing treatment contained formaldehyde, which caused her breathing problems and other health issues. The case led to a class-action settlement of $10.2 million to affected consumers (About Lawsuits, 2021).

  • DMDM Hydrantoin Lawsuits - In 2012, one lawsuit claimed that OGX and TRESemme used DMDM Hydantoin (a formaldehyde releaser) in their shampoo products without proper labeling of the hazards. Continued and still add to their shampoo formulations after announcing in 2012 they would phase out the ingredient (Top Class Actions, 2021). This formaldehyde releaser, along with other listed above, are still allowed to be used in the United States. Most of these lawsuits had to do with proper labeling and transparency, not removing the ingredient due to human health concerns. See which products are covered under these lawsuits here (Class Action, 2024).

  • Benzene in Dry Shampoo - In 2022, an independent lab found levels of benzene in 70% of the 34 brands they tested that exceeded FDA’s limit of 2 parts per million (ppm). Benzene is a known carcinogen that should not be in consumer products should contain this ingredient. Batiste settled for $2.5 Million and other companies are still in the legal process (Lawsuit Information Center, 2024).

  • Olaplex Lawsuits - In 2022 their products were questioned due to the European Union claiming one of their product’s ingredients (Lilial) to be potentially toxic for reproduction. Later in 2023, there were several lawsuits made against Olaplex that were determined by a judge to be too different to consolidate into a class-action lawsuit. Olaplex has taken many steps to be more transparent with their ingredients and testing, as well as phasing out lilial from all products (Forbes, 2024).

Questions

What other products contain formaldehyde-releasing chemicals?

DMDM Hydantoin is a preservative that is used in a wide range of cosmetic and skin care products, in addition to hair care.

What are the harmful ingredients in hair dye or other hair products?

It was clear from our research that there were some other hair products on the market that have higher concentrations of more harmful ingredients than shampoo or conditioner, including hair dye and hair straightener products.

Why is benzene a contaminant in spray consumer products, like dry shampoo?

Benzene has been found in various aerosol personal care products (e.g., spray dry shampoo, spray sunscreen, spray deodorants) as a contaminant by independent testing companies. Although the source is not known, benzene is likely an impurity in petroleum-based distillate streams used to make the propellant (e.g., propane, butane, isobutene) needed for aerosol products. Benzene is a harmful carcinogen that should not be in any personal care product meant for skin contact. Many products have been recalled due to benzene levels higher than FDA’s limit of 2 ppm, like the Batiste lawsuit which found that the dry shampoo contained 15 ppm (Green Matters, 2023).

However, note that benzene is prevalent in the environment from various sources, like cigarette smoke, gasoline, petroleum-based ingredients, forest fires, indoor air, volcanoes, and water sources. The benzene concentration, exposure route (e.g., dermal, inhalation, ingestion), and amount of time of exposure to benzene heavily influences it’s affect on human health outcomes. In general, it may be best to avoid aerosol personal care products where you can, but keep in mind long-term exposure would be the concern here. For instance, using dry shampoo with elevated levels of benzene every day for years. This article provides come good information on benzene in various consumer products and the environment (Chemical & Engineering News, 2021).

References

About Lawsuits. (2021, June). Unilever Suave Shampoo Class Action Lawsuit Filed Over Formaldehyde Problems. https://www.aboutlawsuits.com/suave-formaldehyde-class-action-185130/

Chemical & Engineering News. (2021, December). Finding benzene everywhere we look: Questions pile up as scientists find the carcinogen in more and more consumer products. Chemical & Engineering News, Volume 100, Issue 1. https://cen.acs.org/business/consumer-products/Finding-benzene-everywhere-look/100/i1

Class Action. (2024, July). Lawsuit Investigation:Formaldehyde, Sulfates in Shampoo, Keratin Hair Products. https://www.classaction.org/dmdm-hydantoin-formaldehyde-shampoo-lawsuit

EU. (2009, November). Regulation (EC) No 1223/2009 of the European Parliment and of the Council on cosmetic products. The European Parliament and the Council of the European Union. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex%3A32009R1223

EWG. (2022, February). California bill would ban toxic ‘forever chemicals’ from cosmetics. Environmental Working Group. Accessed on July 24, 2024: https://www.ewg.org/news-insights/news-release/2022/02/california-bill-would-ban-toxic-forever-chemicals-cosmetics.

EWG. (2023, October). Unacceptable List Personal Care Products. Environmental Working Group. Accessed on October 18, 2023: https://static.ewg.org/ewgverified/docs/EWGV_Cosmetics_Program__Active_Unacceptable_List_C02.pdf

IFRA. (2020). p-tert-Butyl-α-methylhydrocinnamic aldehyde (p-BMHCA). International Fragrance Association. https://ifrafragrance.org/pdf/web/viewer.html?file=/standards/IFRA_STD_015.pdf

FDA. (2022). Prohibited & Restricted Ingredients in Cosmetics. Food and Drug Administration. https://www.fda.gov/cosmetics/cosmetics-laws-regulations/prohibited-restricted-ingredients-cosmetics

Forbes (2024, July). Olaplex Lawsuit (2024 Update). Forbes Advisor. Accessed on July 24, 2024: https://www.forbes.com/advisor/legal/product-liability/olaplex-lawsuit/

Flyvholm, M. (2000). Formaldehyde and Formaldehyde Releasers. Handbook of Occupational Dermatology, Chapter 60, 474-478.

FMI. (2024). Beauty and Personal Care / Shampoo Market. Fortune Business Insights (FMI), Accessed on April 21, 2024 at: https://www.fortunebusinessinsights.com/shampoo-market-103432

Geier, J., Uter, W., Pirker, C., Frosch, P. J. (2003, April). Patch testing with the irritant sodium lauryl sulfate (SLS) is useful in interpreting weak reactions to contact allergens as allergic or irritant. Contact Dermatitis, Volume 48, Issue 2. https://onlinelibrary.wiley.com/doi/abs/10.1034/j.1600-0536.2003.480209.x

Government of Canada. (2023, December). Siloxane D5 (cyclopentasiloxane, decamethyl-) - information sheet. https://www.canada.ca/en/health-canada/services/chemical-substances/challenge/batch-2/cyclopentasiloxane-decamethyl.html

Green Matters. (2023, August). Batiste Dry Shampoo Settles Lawsuit for $2.5 Million Over Traces of Carcinogen. https://www.greenmatters.com/big-impact/batiste-dry-shampoo-lawsuit#:~:text=After%20publicizing%20the%20research%2C%20Valisure,of%202%20ppm%20for%20drugs.

Lawsuit Information Center. (2024, June). Batiste Dry Shampoo Cancer Lawsuit. Accessed on July, 24, 2024: https://www.lawsuit-information-center.com/batiste-dry-shampoo-cancer-lawsuit.html

Maneli, M., Smith, P., Kumalo, N. (2014, February). Elevated formaldehyde concentration in “Brazilian keratin type” hair-straightening products: A cross-sectional study. Journal of the American Academy of Dermatology, Volume 70, Issue 2, 276-280. https://doi.org/10.1016/j.jaad.2013.10.023

NSF. (2023, October). Cosmetics and Personal Care Program. National Sanitation Foundation, Accessed on October 19, 2023 at: https://www.nsf.org/consumer-resources/articles/cosmetic-personal-care-program

NYT. (2023, October). F.D.A. Plans to Ban Hair Straighteners With Formaldehyde. New York Times. https://www.nytimes.com/2023/10/16/health/hair-straighteners-black-women-fda.html

OAG CA. (2012, January). Attorney General Kamala D. Harris Announces Settlement Requiring Honest Advertising over Brazilian Blowout Products. Offices of the Attorney General of California. https://oag.ca.gov/news/press-releases/attorney-general-kamala-d-harris-announces-settlement-requiring-honest

OEHA. (2018, August). Cocamide Diethanolamine (Cocamide DEA) (Coconut Oil Diethanolamine Condensate). Office of Environmental Health Hazard Assessment. https://www.p65warnings.ca.gov/sites/default/files/downloads/factsheets/cocamide_diethanolamine_fact_sheet.pdf

Punyoyai, C. et al. (2018, July). Development of Antidandruff Shampoo from the Fermented Product of Ocimum sanctum Linn. Cosmetics, Volume 5, Issue 3, 43. https://www.mdpi.com/2079-9284/5/3/43

Rai S., Dasani, S. (2014, January). The Science of Shampoo: Herbal vs. Synthetic. Srujan Volume 3, Isssue 1, 49-54. https://kccollege.edu.in/wp-content/uploads/2021/08/2013-14_Srujan_V-3_Is-1.pdf#page=54

SCCS. (2019, May). OPINION ON the safety of Butylphenyl methylpropional (p-BMHCA) in cosmetic products - Submission II. Science Committee on Consumer Safety. https://health.ec.europa.eu/system/files/2021-08/sccs_o_213_0.pdf

State of California. (2020, September). Assembly Bill No. 2762. State of California Department of Public Health. https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=201920200AB2762

State of Maryland. (2021, May). House Bill 643: Public Health – Cosmetic Products – Ingredient Prohibition. Lawrence J. Hogan, Jr., Governor. https://mgaleg.maryland.gov/2021RS/Chapters_noln/CH_490_hb0643t.pdf

State of Washington. (2023, May). Substitute House Bill 1047. Secretary of State State of Washington. https://lawfilesext.leg.wa.gov/biennium/2023-24/Pdf/Bills/Session%20Laws/House/1047-S.SL.pdf?q=20230518151640

Top Class Actions. (2021, August). OGX Shampoo, TRESemmé, WEN: Johnson & Johnson not the only brand to be accused of putting dangerous chemicals in shampoo. https://topclassactions.com/in-depth/ogx-tresemme-wen-shampoo-lawsuits/

Anna Dimling