There is not much evidence to suggest that chemicals in shampoo can cause permanent hair loss. Some ingredients may be drying, though, which could increase the risk of hair breakage.

To keep their hair healthy, people with dry or brittle hair may wish to avoid shampoos that contain certain substances, such as keratin or strong dyes.

There are other aspects of hair care that can also affect hair health. Certain brushing or styling methods may lead to pulling or breakage.

This article will look at some of the chemicals shampoos can contain and how likely they are to cause hair loss.

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Many factors can lead to hair loss, but the American Academy of Dermatology (AAD) does not list shampoo as one of them.

However, some research suggests certain substances in shampoos may damage the hair, which could lead to breakage. There are also methods of brushing or styling the hair that can cause breakage.

The Food and Drug Administration (FDA) does not test shampoos for safety before sale. However, by law, manufacturers must test products rigorously before they go on sale. Shampoos cannot contain any ingredient that might be harmful when used according to the instructions.

Below are some of the ingredients that may be problematic for hair health.

Sulfates are a group of ingredients known as surfactants. They help clean the hair. Some sulfates, such as sodium lauryl sulfate (SLS), can be harsh and drying, but others are gentler.

According to an older 2015 study, many shampoos used to contain SLS, but most now use a different sulfate known as sodium laureth sulfate. This ingredient has a moisturizing effect

and tends to cause fewer problems for the scalp and hair than SLS.

Still, some people find they are sensitive to other sulfates. They can remove natural oils from the skin and hair, leaving hair dry and possibly brittle. This may make it more prone to breakage.

People with dry, brittle hair may find a sulfate-free shampoo less likely to cause damage, although they will likely need a clarifying shampoo that contains sulfates every 15 days or so to prevent the buildup of oil or hair products.

Formaldehyde is used in certain cosmetic products as a preservative and nail hardener. Global health agencies do not permit formaldehyde in other cosmetic products, though.

As a result, people generally do not need to worry about formaldehyde being in shampoo.

However, some keratin treatments do release high levels of formaldehyde. This is not a shampoo but a hair-smoothing procedure some salons offer.

Formaldehyde is also known as formalin or methylene glycol. This substance can cause cancer, as well as skin irritation, allergic reactions, headaches, dizziness, and severe irritation in the nose, mouth, and lungs.

Because keratin treatments involve heat, they can also cause hair damage. The FDA has issued warnings about the use of hair products that release formaldehyde and is planning to ban these treatments.

Some shampoos contain small amounts of dye to tint or color the hair. Shampoos containing temporary dyes are unlikely to cause damage, as they do not penetrate the hair.

However, a 2023 Korean study found that shampoos containing trihydroxybenzene-based dyes can harm the skin barrier on the scalp. These are stronger dyes with a longer-lasting effect that people may use to change their hair color rather than just boost their natural tints.

Any dyes used in shampoos must have FDA approval. Manufacturers can only use the percentage of color agreed upon with the FDA for the intended purpose.

Some dyes need FDA certification. Dyes from mineral, plant, or animal sources do not need certification, but they must still meet FDA requirements.

Keratin is a protein and a key component of hair. When people use shampoos with added keratin, the keratin coats the hair, making it look shiny and healthy. It does not cross the hair barrier to add protein to the hair.

However, coating the hair with keratin may mean less hydration can penetrate the hair shaft during shampooing. Anecdotally, some people report that the long-term use of keratin results in dry or brittle hair.

Some people use coal tar shampoo to manage itching and irritation of the scalp, including scalp psoriasis. For some people, however, it can cause irritation and may lead to dry and brittle hair.

Products containing coal tar must carry a warning, and people should do a patch test before using it more liberally.

Some people wonder if silicones in shampoo and conditioner can cause hair loss. There is no scientific evidence for this.

The silicones in hair products aim to increase hair body, protect the hair shaft, and boost moisture levels. Examples include dimethicone.

Shampoo alone is unlikely to cause hair loss, but many other factors can increase the risk, such as:

People experiencing hair loss should contact a doctor or dermatologist to understand what might be causing it, as it can sometimes be a sign of an underlying condition.

A doctor can help identify what type of hair loss it is and suggest effective treatments. This may involve changing to a gentle, nonirritating shampoo, as well as using gentle methods to style the hair.

But there are also treatments for some types of hair loss that prevent excessive shedding and stimulate growth.

People experiencing hair loss may wonder if their shampoo is causing it. This is possible, but there is little evidence that chemicals in shampoo are a major culprit for hair loss.

However, some shampoo ingredients and hair styling methods can cause hair breakage. This may reduce how thick the hair appears if the damage is extensive.

People who are unsure of what is causing their hair loss can speak with a doctor for advice.