HomeIn the newsHair straightening products are safe and do not cause cancer

Hair straightening products are safe and do not cause cancer

You may have seen media reports of a new study published in the Journal of the National Cancer Institute which claims to find an association between the use of hair straighteners and uterine cancer.

View the study here: Journal of National Cancer Institute

At CTPA, we understand that such reports can cause alarm.  Our scientific team has looked into the science of the study in detail, and it does not show that hair straighteners are unsafe or that their ingredients cause cancer.  The reasons for these conclusions are explained below. 


Dr Emma Meredith, Director-General of CTPA and a pharmacist says:    
Just like all cosmetics and personal care products, cosmetic hair straighteners must be confirmed as safe for us to use before they are allowed to be sold.  Companies put their ingredients and products through years of development and a legally required in-depth safety assessment, part of which must rule out any risk of the ingredients causing cancer. Not only do companies do this because safety is their highest priority, but also because the UK has strict laws dedicated to the safety of cosmetics. 
Understanding relationships between potential risk factors and diseases can be difficult and this study gathered data on many different characteristics and lifestyle factors, several of which were associated with a higher risk of uterine cancer. However, the study did not gather information on which hair products were used by the women, or their ingredients, so it cannot make a link between hair straighteners and cancer. 

How the study was conducted 

The ‘Sister Study’ is a USA-based research programme which enrolled just over 50,000 women, who had at least one sister diagnosed with breast cancer.  The women’s characteristics and lifestyle factors were recorded, including age, ethnicity, education, Body Mass Index (BMI), smoking and alcohol status, along with how often they used different hair products.  The women were contacted again regularly for 10 years after enrolling in the study for health updates regarding new cancer diagnoses and other health-related changes. 

Analysis of the study findings 

One factor doesn’t necessarily cause another 

The study authors reported that women within the study who had uterine cancer were more likely to have used hair straightening products at least once over the past 12 months than the rest of the women in the study. 

However, the study also found that women who had uterine cancer were more likely to be older, less physically active and have a higher BMI than the rest of the women in the study.  Therefore, the study could equally have linked any of these other factors to a higher risk of uterine cancer in its conclusion.  When looking at scientific studies which report an association between two factors, it is important to consider whether there could be something else that is either responsible for, or contributing to, a study result.  Just because two factors are associated, it doesn’t mean that one has caused the other.  For example, the women with uterine cancer were also slightly more likely to have a college degree than the overall study average, but it wouldn’t make sense to suggest that having a college degree has any causative role in uterine cancer.    

The suggested reasons for an association between hair straighteners and cancer are unfounded 

The authors suggest that use of hair straighteners and uterine cancer may be related because of certain ingredients in the products.  However, the study did not gather data on which products were used or their ingredients.  In fact, several chemicals suggested by the authors as possibly being responsible for a link between these products and cancer, i.e. phthalates and bisphenol A, are either banned or not used in cosmetics. 

The study found that the use of other hair products such as hair dyes was not associated with an increased risk of uterine cancer, yet these products are likely to contain a number of the same, safe, ingredients as straighteners.  In fact, women who had used hair dyes over the past 12 months were less likely to have uterine cancer than those who had not used hair dyes.  This illustrates how unreliable it is to take an association between two factors to say that one causes, or protects against, the other. 

All cosmetics and personal care products must be safe by law 

All cosmetic products sold in the UK are regulated by strict UK legislation. The most important purpose of these laws is to protect the safety of those who use cosmetics.  

All ingredients in cosmetics and personal care products undergo much research, carried out by both industry expert scientists and independent scientists reporting to authorities across the world, before being introduced to the market.  Also, every single cosmetic product must be approved by a safety expert before being sold. 

This safety assessment looks at the wealth of science behind the ingredients, who uses the products, how and where they are used and how often over a lifetime.  Once on sale, companies continue to monitor consumers’ use of their products, for example by recording and monitoring any undesirable reactions, as well as reviewing any new science that becomes available, to confirm the safety of products on an ongoing basis. 

We can have confidence in the safety of our hair straighteners and all cosmetic products. 

More information about the safety of hair products can be found here

For further information about interpreting scientific study results, Sense About Science has a helpful guide: ‘I don’t know what to believe’.

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