Published: 01 February 2022  (Updated: 11 March 2022)

Is your shampoo making you fat? … How can you be sure?

By Caroline Rainsford, Head of Scientific Services, CTPA



Last week, a headline in a national newspaper article caught my eye. Based on a study from researchers at the Norwegian University of Science and Technology (NTNU), the headline suggested that chemicals found in shampoo bottles could be making us fat.

Applying findings from new scientific research to our daily lives is a crucial part of ensuring that science stays relevant and holds our attention.  Unfortunately, as with everything in life, it’s not always straightforward to use findings from a scientific study to explain bigger phenomena in our lives.  Starting with a few simple questions, you can ‘interrogate’ media articles to come to your own conclusions about whether shampoo makes you fat, and other stories.

Let’s take a look behind this headline.  The premise of the article is that a number of ‘metabolism-disrupting’ chemicals that can be attributed to weight gain have been detected in personal care product packaging.  Sounds concerning, right? But let’s look a little closer…

It’s certainly true that the study’s authors looked at packaging samples and found some of these samples contained chemicals they suspect to have metabolism-disrupting effects…. just not the shampoo bottles! In contrast to what the striking headline suggests.

A little further down in the study, the authors found that plastic extracts from the shampoo bottles they tested didn’t have an effect on the development of fat cells. An important fact overlooked by the newspaper story headline.

However, even if shampoo bottles are off the hook, does that mean we need to worry that other plastic packaging could be making us fat?  To answer this question, it’s good to ask why the authors suspect that some chemicals might have metabolism-disrupting effects, and how they tested this.

The authors begin with the ‘obesogen hypothesis’ which is a line of thought that some chemicals might contribute to obesity by promoting the growth and behaviour of fat cells or by impacting our metabolism.

Therefore, the chemicals from each piece of plastic packaging were extracted and concentrated into a solvent to be used as a sample for testing.  This sample, containing the chemicals from the plastic packaging, was tested on fat cells grown in a lab. 

The purpose of this part of the study was to see whether the chemicals promoted the growth of the fat cells or could impact part of the system within our bodies which regulates how fat is deposited.  The findings? Some of the samples did have an effect on growth of the fat cells.

The results from the study certainly give us a fascinating insight into the behaviour of fat cells in the presence of certain chemicals. Although we do have to consider what might happen outside of a lab? What do the findings mean for real life? Scaling this up to a real-life-relevant level raises two important questions.  Are we exposed to the same amount of chemicals from plastic packaging when using everyday products?  How will the chemicals get into our bodies?

Let’s take these questions one at a time, starting with our likely exposure to chemicals. 

To extract chemicals from the plastic packaging, the study’s authors had to use something called a solvent which also had to be really good at dissolving them in order to obtain enough chemicals so that they could do the tests. In this particular study, a solvent called methanol was used.

Importantly, the reality is that a shampoo, or a drink, are far less effective than methanol at dissolving chemicals so in a real-life situation, the vast majority of chemicals present in the plastic packaging will stay securely within the plastic itself. 

In fact, the laws covering cosmetics, food and many other consumer products already take into account the possibility that chemicals could migrate from the packaging into the product.  Strict legal requirements are in place meaning that any potential migration must be investigated to ensure this doesn’t put our safety at risk.

Second up, let’s look at how those chemicals might get into our bodies to get to our fat cells….

In the test, the chemicals were directly added to the fat cells.  This is certainly a short-cut versus how our bodies are exposed to chemicals in real life.  Take the example of food. When we eat food, it has to travel down to our digestive system and be broken down through numerous processes. Then the broken-down products are sorted and transported around our systems to where they are needed in our bodies, or removed if not needed.

Within this hugely complex process, there are many opportunities for chemicals to be trapped, removed or broken down into something else…  They don’t just head straight towards the fat cells.

Now take the example of personal care products. These are applied to our skin or hair where it is far more difficult for the ingredients to even pass through the body’s extremely effective barrier system - our skin.  Nevertheless, this possibility is all taken into account in the cosmetic safety assessment, which ensures that ingredients are safe.

In short, if we were to consume a chemical or apply one to our skin, it’s far less straight- forward for that chemical to reach our metabolic system than the fast-track route taken in the lab.

Finally, it’s important to consider whether there could be something else that is either responsible for, or contributing to, a study result.  In this case, we know that there are many factors behind obesity which are complex and interlinked.  Linking obesity to a single cause is likely to be an oversimplification.

It’s always exciting to see new scientific research, especially that which relates to the cosmetics and personal care industry – which has science at its foundation.  Research drives new innovations in product performance, safety and sustainability and can help us focus on areas where more science is needed to address data gaps or uncertainties. 

But this headline-grabbing story is a reminder that in every case, it is helpful to approach new science with a critical eye, an open mind… and to draw your own conclusions.

If you’d like to take a look at the original study paper, you can find it here.

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