Some ingredients frequently used in shampoo can be harmful to your hair or even your health.
Shampoo Ingredients That Can Hurt Hair
Experts say skip shampoos with these ingredients, as they may be damaging to hair.
1. Alcohol(Some of Them)
Alcohol is commonly found in shampoos, conditioners, and styling products because it helps your skin and hair absorb active ingredients. But short-chain alcohols (including isopropyl alcohol) can irritate the skin and dry out the hair, according to Consumer Notice, a nonprofit consumer advocacy organization that educates the public about harmful products. Ethanol is another short-chain alcohol that can also leave the hair feeling dry and brittle, says Ross Kopelman, DO, a hair restoration surgeon with Kopelman Hair Restoration in New York City.
That said, fatty alcohols like cetyl alcohol, stearyl alcohol, and cetearyl alcohol have the opposite effect. “They help condition the hair and retain moisture,” says Dr. Kopelman, who notes that fatty alcohols can be especially helpful for people with dry or damaged hair.
2. Coal Tar
Coal tar is a petroleum by-product that’s used in permanent hair dyes, with darker dyes containing higher amounts. It’s commonly added to shampoos to treat scalp psoriasis.
There’s some concern that coal tar may be a carcinogen, but the American Cancer Society notes that studies haven’t found a strong link so far. “Dermatologists prescribe coal tar shampoos for scalp psoriasis if needed and it is considered safe for long-term use,” Dr. Kazin says. Note, however, that using the products too often or on a sensitive scalp may cause hair loss or burning, itching, tingling, pain, or redness.
People who are pregnant or breastfeeding should avoid coal tar in psoriasis shampoos and hair dyes altogether, given the lack of research on its effects in this group, Kazin says.
3. Polyethylene Glycols
Polyethylene glycols (PEGs) are petroleum by-products used to thicken hair care products. Past research shows PEGs are generally safe when used in cosmetics.
But researchers are still examining a potential link between PEGs and severe scalp irritation and skin damage. Moreover, some PEGs may be contaminated with harmful substances like 1,4-dioxane, which is a known carcinogen, Kopelman says.
PEGs can be listed on product labels in different ways. They often appear as “PEG” followed by a number (such as PEG-40) or “PEG” followed by a number and then another ingredient name (such as PEG-20 cocamine).
4. Selenium Sulfide
Selenium sulfide, an anti-infective agent, is often used in medicated shampoos to treat dandruff-related itching and flaking. But this ingredient can irritate the scalp and cause permanent hair loss if used too frequently.
“I generally advise patients to limit their use of selenium sulfide to two to three times per week at most,” Kopelman says. If your scalp becomes more sensitive or you notice hair thinning, alternate the selenium sulfide shampoo with a gentler shampoo that contains zinc pyrithione or tea tree oil, suggests Kopelman.
5. Silicones
Silicones are added to hair-care products to make your hair soft and smooth. But these ingredients build up with repeated use, preventing moisture from getting into your hair cuticles. This can cause skin irritation, dry hair, and flat curls.
Check hair-care product labels for these common silicones:
Dimethicone
Phenyl trimethicone
Cyclomethicone
Cyclopentasiloxane
Cyclohexasiloxane
Shampoo Ingredients That May Be Damaging to Overall Health
Many shampoo ingredients that can be harmful to the hair and to overall health have become much less common as research by dermatologists has highlighted the risks and products have been reformulated, says Mary Lupo, MD, a dermatologist at the Lupo Center for Aesthetic & General Dermatology in New Orleans.
But several potentially harmful ingredients are still regularly found in shampoos, including the following.
1. Benzene
Benzene is a colorless liquid chemical that’s commonly used in hair dyes. It may be carcinogenic with long-term use, and may contribute to birth defects and damage the immune and nervous system in people who are pregnant.
In October 2022, the U.S. Food and Drug Administration (FDA) found elevated levels of benzene in dry shampoo products. In response, dry shampoo manufacturers pulled benzene-containing products from store shelves. Since you may have purchased these products before they were recalled, be sure to check the label of any dry shampoo you have at home.
To ensure your hair product doesn’t include benzene, check the label for these ingredients:
Benzene
Toluene
Methylbenzene
Phenylmethane
Toluol
2. Resorcinol
Resorcinol is a bleaching agent commonly found in hair dyes and treatments for dandruff and scalp psoriasis. It may interfere with the creation of thyroid hormones, impacting thyroid function and increasing the risk of hyperthyroidism (where the thyroid creates too many hormones). Resorcinol may also cause breathing problems and disrupt the nervous system.
“Ultimately, it’s about balancing effectiveness with safety, and for patients with chronic scalp conditions, I encourage discussing options with a dermatologist or hair specialist,” Kopelman says.
To avoid resorcinol, check hair dyes and products for the following ingredients:
Resorcinol
1,3-benzenediol
Resorcin
1,3-dihydroxybenzene
3. Diethanolamine
Diethanolamine (DEA), commonly used as a foaming agent or to adjust the pH balance in hair products, is a possible carcinogen. Research has found a link between DEA and cancer in laboratory animals, but not humans. “DEA is classified as a potential allergen but the FDA does not restrict it for health reasons,” Kazin says.
4. Triclosan
Triclosan is an antibacterial agent that was used in soaps — until data suggested that long-term exposure could disrupt hormones. This led the FDA to ban triclosan from antibacterial soaps in 2016. But triclosan is still used as an antibacterial agent in shampoos.
5. Formaldehyde and Formaldehyde-Releasing Preservatives
Formaldehyde is a colorless, strong-smelling gas found in cigarettes, building materials, and industrial cleaning products. It’s also added directly to or released from preservatives in shampoo and chemical hair-straightening treatments, and is linked to an increased risk of cancer.
Formaldehyde and formaldehyde-releasing preservatives can also cause allergic skin reactions.
Check shampoo, conditioner, and chemical hair straightener labels for formaldehyde (also referred to as methylene glycol and formalin) and preservatives that release formaldehyde. These include:
Quaternium-15
Imidazolidinyl urea
Diazolidinyl urea
Polyoxymethylene urea
Sodium hydroxymethylglycinate
Glyoxal
6. Parabens
There’s concern that parabens, which help extend the shelf life of shampoo, may disrupt your hormone balance, reproductive health, and nervous system and cause skin irritation. The FDA says no research currently shows that parabens affect human health.
In addition, research shows that parabens are less likely than other preservatives to cause allergic reactions, Kazin says.
Still, if you’d like to avoid hair products with parabens, check the label for ingredients ending in “paraben,” such as:
Butylparaben
Ethylparaben
Methylparaben
7. Synthetic Fragrances
Many manufacturers use fragrances to give shampoo and conditioner a pleasant scent. But these fragrances are often synthetic and may be created with chemicals that harm your skin, hair, and health. These chemicals may contribute to infertility, skin irritation, hair loss, asthma, and cancer.
“Fragrance blends often contain dozens of unlisted chemicals, which makes it difficult to determine exactly what you’re putting on your scalp,” says Kopelman. “While not everyone will have a reaction, I recommend patients opt for fragrance-free or naturally scented shampoos when possible, especially if they have scalp sensitivity, hair thinning, or hormonal concerns.”
To determine whether a shampoo has synthetic fragrance, Kopelman suggests checking the ingredient list for terms like “fragrance” or “parfum.”
8. Phthalates
Research suggests that phthalates, which enhance the fragrance of shampoo, may disrupt hormones. Pthalates are banned in Canada, but don’t need to be named on U.S. ingredient labels — they can simply be listed as “fragrance.”
Some companies label their products “phthalate-free.” Otherwise, check for these phthalates:
Butyl benzyl phthalate (BBP)
Diethyl phthalate (DEP)
Diisodecyl phthalate (DIDP)
Diisononyl phthalate (DINP)
Dihexyl phthalate (DHP)
Dioctyl phthalate (DNOP)
9. Sulfates
Sulfates, which create lather and bubbles in shampoo, can irritate the skin and eyes and trigger an allergic reaction. These ingredients can also dry out the skin and make hair frizzy.
Sulfates commonly used in shampoos include:
Ammonium lauryl sulfate
Sodium lauryl sulfate (SLS)
Sodium laureth sulfate (SLES)
SLES in particular may contain traces of 1,4-dioxane, a carcinogen that has contributed to cancer development in lab animals.
