4 Potentially Carcinogenic Hair Care Ingredients No One Should Be Using In 2025

September 2, 2025 by Lisa Cupido

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These days, most hair care products on store shelves are much safer than they used to be. We have a growing awareness around clean beauty and stricter regulations in place, and many brands have made great strides in removing harsh or harmful ingredients from their formulas. That means we have more options than ever when it comes to shampoos, conditioners, and styling products that are both effective and gentle on our hair and scalp.

But it’s still a smart idea to stay informed about what’s in your products. Some ingredients linked to potential health risks—like hormone disruption or even cancer—can still sneak their way into certain formulas, especially in lesser-known products. If you’re looking to make better choices for your long-term hair and scalp health, here are a few potentially carcinogenic ingredients worth avoiding.

1. Formaldehyde

Formaldehyde is sometimes found in hair straightening or smoothing treatments, and it's often listed as formaldehyde-releasing agents (like DMDM hydantoin or quaternium-15). Formaldehyde is a known human carcinogen, particularly when inhaled in significant amounts over time. The risk is highest in salon settings where heat is applied and fumes are released, which is why both professionals and consumers are advised to use caution. Thankfully, many at-home products containing formaldehyde have been regulated or banned in many countries.

2. Coal Tar

Coal tar is occasionally used in medicated shampoos to treat scalp conditions like psoriasis and dandruff. While it's effective, coal tar contains polycyclic aromatic hydrocarbons, some of which are linked to cancer in animal studies. Coal tar is classified as a possible human carcinogen, particularly with prolonged or high exposure. However, the amounts used in over-the-counter shampoos are considered low risk for most people.

3. Parabens

Parabens are preservatives used to prevent mold and bacteria in cosmetics. Some studies suggest they can mimic estrogen in the body, which has led to concerns about a potential link to hormone-related cancers such as breast cancer. But it's important to keep in mind that current evidence does not confirm a direct causal relationship between parabens in cosmetics and cancer, and parabens are considered safe at low concentrations. If you are concerned, choose paraben-free formulas.

4. Phthalates

Phthalates are often used to help fragrances last longer in hair and personal care products. Some phthalates have been linked to endocrine disruption, and certain types (like DEHP) are classified as possibly carcinogenic to humans. The concern is mostly about long-term exposure, particularly for vulnerable populations like pregnant women.

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