The "best" shampoo is subjective and can depend on individual needs and preferences. However, we can advise on chemicals to avoid in shampoos and other hair products due to potential health hazards.

Step 1: Avoid Harmful Chemicals in Shampoos and Hair Products

Several chemicals commonly found in hair products, including shampoos, have been linked to various health concerns:

• P-phenylenediamine (PPD): Commonly used in hair dye, PPD is a significant trigger for allergic reactions, some of which can be life-threatening (Women's Voices for the Earth, 2023). It can cause severe dermatitis, asthma, and rhinitis, particularly in salon workers (Women's Voices for the Earth, 2023). The chemically similar p-phenylenediamene sulfate, introduced as a "safer" alternative, is also a potent skin sensitizer, frequently leading to dermatitis upon exposure (Women's Voices for the Earth, 2023).

  
  

• Triclosan: An antimicrobial that extends shelf life, triclosan is associated with skin irritation, contact allergic dermatitis, and antibiotic resistance with prolonged use and high concentrations (Caterbow & Hausmann, 2016). It is thought to disrupt the balance of microorganisms in the skin microbiome and has been banned as an anti-microbial wash in some countries (Caterbow & Hausmann, 2016). Triclosan has been found in the urine of three-quarters of the US population (Caterbow & Hausmann, 2016).

  
  

• Parabens: These are a group of chemicals frequently used as preservatives in cosmetics, body creams, hair products, and sunscreens (Caterbow & Hausmann, 2016; James-Todd et al., 2021). They can be absorbed through the skin and have been linked to breast cancer due to their hormone-disrupting properties (Breast Cancer Prevention Partners, n.d.; James-Todd et al., 2021; Caterbow & Hausmann, 2016). Shampoos, conditioners, and facial cleansers are among the products where parabens are commonly found (James-Todd et al., 2021). Studies show Black women often have higher concentrations of certain parabens (James-Todd et al., 2016; James-Todd et al., 2021). Parabens can act as estrogen agonists and androgen antagonists (James-Todd et al., 2021). Exposure to parabens has been associated with increased risk of preterm birth (Amine et al., 2025). Early-life exposure to mixtures of parabens was also associated with poorer child health scores in one study (Amine et al., 2025).

  
  

• Fragrances/Perfumes: Many products, including shampoos and conditioners, contain synthetic fragrances (James-Todd et al., 2021). Manufacturers are often not required to list individual chemicals in fragrances, which can include harmful substances (Harvard T.H. Chan School of Public Health, n.d.; Women's Voices for the Earth, 2023). These hidden chemicals may contribute significantly to chemical exposure via the skin (Harvard T.H. Chan School of Public Health, n.d.; Women's Voices for the Earth, 2023). Common fragrance ingredients found in hair products include phthalates (like Diethyl phthalate or DEP), lilial, galaxolide, and others that can be endocrine disruptors, carcinogens, reproductive toxicants, respiratory toxicants, or environmental hazards (Harvard T.H. Chan School of Public Health, n.d.). For example, lilial is a reproductive toxicant prohibited by the European Union and was common in hair products in one study (Women's Voices for the Earth, 2023). A new California law requires cosmetics manufacturers to report toxic fragrance and flavour ingredients to the California Safe Cosmetics Program, making this information publicly available for products sold in California (Women's Voices for the Earth, 2023).

  
  

• Formaldehyde and Formaldehyde-Releasing Preservatives (FRPs): Formaldehyde and FRPs are used in personal care products, including shampoos, to prevent microbial growth (Dodson et al., 2025). Formaldehyde is classified as a known human carcinogen and can cause allergic contact dermatitis (Dodson et al., 2025). Exposure can occur through skin absorption or inhalation during product use (Dodson et al., 2025). DMDM hydantoin and diazolidinyl urea are common FRPs found in hair and skin products, with DMDM hydantoin being able to release two equivalents of formaldehyde (Dodson et al., 2025). Hair products containing formaldehyde can cause allergic reactions, breathing problems, and chronic health issues (Women's Voices for the Earth, n.d. Formaldehyde in Brazilian Blowout, Hair Straighteners). The EU has banned formaldehyde as a cosmetic ingredient, and California will ban formaldehyde and certain FRPs from cosmetics sold in the state effective 2025 (Dodson et al., 2025). Over half of participants in a South Los Angeles study reported using at least one personal care product with formaldehyde or FRPs, even though only a small percentage of products listed these as ingredients (Dodson et al., 2025).

  
  

• 1,4-Dioxane: This is a potential human carcinogen found mainly in shampoos and liquid hand and body soaps as an undesirable by-product of the manufacturing process (Caterbow & Hausmann, 2016).

  
  

• Cocamide diethanolamine (Cocamide DEA): Listed as a carcinogen on California’s Proposition 65 list, cocamide DEA is used as an emulsifier/surfactant and has been found in shampoos and body wash (Caterbow & Hausmann, 2016).

  
  

• Cyclopentasiloxane/Cyclomethicone: These can create formaldehyde under the high heat of styling tools like flat irons, leading to formaldehyde exposure symptoms such as breathing problems, coughing, and skin rashes (Women's Voices for the Earth, n.d. Formaldehyde in Brazilian Blowout, Hair Straighteners).

  
  

• Ammonium Hydroxide, Calcium Hydroxide, Sodium Hydroxide (Lye): These are highly corrosive chemicals found in hair relaxers (Women's Voices for the Earth, 2023; Scranton, 2014). They can cause scalp lesions, burns, and hair loss (Women's Voices for the Earth, 2023). Hair relaxer use has been linked to uterine fibroids (Scranton, 2014) and an increased risk of breast and uterine cancer (Scranton, 2014).

  
  

• Thioglycolic acid / Ammonium thioglycolate: Found in permanent wave solutions and hair relaxers, these are skin sensitizers and have potential reproductive harm (Scranton, 2014).

  
  

• Persulfate Salts (Ammonium persulfate, Potassium persulfate): Used in hair bleaches, these are strong skin and lung irritants, linked to breathing problems and chemical burns on the scalp in hairdressers (Women's Voices for the Earth, 2023; Scranton, 2014).

  
  

• Hair oils, lotions, and leave-in conditioners: These products, commonly used by Black women, have been shown to contain mixtures of endocrine-disrupting chemicals (EDCs) like phthalates, parabens, and phenols, and can be hormonally active (James-Todd et al., 2021; Preston et al., 2021). A pilot study found that frequent or daily use of hair oils during late pregnancy was associated with earlier gestational age at delivery (Preston et al., 2021). Leave-in conditioners and hair oils showed the highest degree of hormonal activity, impacting estrogen, androgen, progesterone, and glucocorticoid receptors (James-Todd et al., 2021).

  
  

Step 2: How to Choose Shampoos and Hair Products

To minimise exposure to harmful chemicals:

• Read the label carefully: In the European Union, all cosmetics must list their ingredients, making it easier to avoid harmful chemicals such as triclosan and parabens (Caterbow & Hausmann, 2016). Outside the EU, choosing cosmetics approved and sold in the EU may result in fewer harmful chemicals due to the EU's stricter chemical regulations (Caterbow & Hausmann, 2016).

  
  

• Avoid synthetic fragrances: Many products, including shampoos, do not require synthetic fragrances to be effective (Harvard T.H. Chan School of Public Health, n.d.). When you see "fragrance," "perfume," or "parfum" on a label, be aware that it can hide a multitude of undisclosed harmful chemicals, including phthalates (Harvard T.H. Chan School of Public Health, n.d.). Choosing unscented products can reduce exposure to these unlisted chemicals (Caterbow & Hausmann, 2016).

  
  

• Look for specific labels: Opt for products labelled "paraben-free" or those that do not contain chemicals with "fluoro" in the name or "PTFE" to avoid PFAS (Harvard T.H. Chan School of Public Health, n.d.).

  
  

• Be wary of "natural" or "organic" claims: Even products marketed as "natural" or "organic" may contain hazardous ingredients or interact with synthetic chemicals to increase toxicity (Alnuqaydan, 2024; Harvard T.H. Chan School of Public Health, n.d.). These labels do not automatically guarantee safety (Alnuqaydan, 2024).

  
  

• Reduce overall product use: One study found that women use an average of 8 products a day, with some using up to 30, leading to exposure to a mixture of chemicals (Caterbow & Hausmann, 2016). Reducing the number of products used can help limit exposure (Caterbow & Hausmann, 2016).

  
  

• Seek out eco-labels: Look for products with an ecolabel, as these can indicate a reduced risk of exposure to harmful chemicals (Caterbow & Hausmann, 2016).

  
  

• Stay informed: Utilise resources such as the IFRA Transparency List and the Campaign for Safe Cosmetics to help identify and avoid potentially harmful ingredients (Harvard T.H. Chan School of Public Health, n.d.; Campaign for Safe Cosmetics, n.d.).

In summary, while there isn't a single "best" shampoo identified, focusing on avoiding products with known harmful chemicals like PPD, triclosan, parabens, undisclosed fragrances, formaldehyde-releasing agents, 1,4-dioxane, and corrosive relaxer components will help consumers make safer choices.