Do Hair Dye and Hair Relaxers Increase Cancer Risk?

If you’re one of the millions of people who use hair products, you may have heard about a possible link between using hair dye or relaxers and your risk of cancer. 

So far, it’s not clear if using hair dye increases your risk of developing cancer. Hundreds of studies have looked into this question. But the results aren’t definitive: Some have shown a link between hair dye and cancer, while others have not. There are also studies — though fewer in number — on the link between hair straighteners/relaxers and cancer risk. Those results are also mixed: Some have shown a link, while others have not. 

Here we’ll take a look at hair dye and chemical straighteners/relaxers and see what the current scientific evidence says about whether or not they may cause cancer.

What is the link between hair dye and cancer?

Some of the first hair dyes had chemicals that were found to cause cancer in lab animals. This included chemicals called aromatic amines that could cause different types of urinary tract (urothelial) cancers, like bladder cancer. 

This discovery caused several governing bodies, like the European Union, to ban some of these chemicals — but not all of them. Hair dyes still contain thousands of different chemicals, and research continues to look at whether using hair dye is associated with increased cancer risk. 

Some studies have shown a link between hair dye and cancer, but others have not. A link doesn’t mean that hair dye causes cancer. It just means that hair dye could be a risk factor (among many others) for cancer.

You may be surprised that studies can show such different results. There are many reasons for these differences. Consider the following:

• Small studies may not have enough people to show a clear result.

• People can have a hard time accurately remembering their use of hair dyes or hair relaxers (called “recall bias”).

• Hair dyes have changed over time.

• Studies aren’t always designed well (they have short follow-up, or don’t include all cancer-specific risks).

Are hair dye or hair relaxers carcinogens?

Hair dyes and hair relaxers can contain over 5,000 different chemicals. Some of them, like DMDM hydantoin and imidazolidinyl urea, can slowly form a chemical called formaldehyde. Most hair smoothing or straightening products also release formaldehyde into the air during the treatment process. Some organizations classify formaldehyde as a “human carcinogen,” which means it can cause cancer or help cancer grow in especially high amounts.

 These health organizations have looked at whether hair dye or their ingredients can cause cancer:

• International Agency for Research on Cancer (IARC): The IARC doesn’t classify personal hair dye as a cause of cancer. But the IARC classifies exposure to hair dye at work — like at a salon for hairdressers — as “probably carcinogenic.” 

• National Toxicology Program (NTP): The NTP hasn’t classified hair dyes as causing cancer. But it states that some of the chemicals in hair dyes are “reasonably anticipated to be human carcinogens.”

Which types of cancer have been linked with hair dye or relaxers?

The strongest link between cancer and hair dye has been with bladder cancer in people exposed to semipermanent and permanent hair dye at work (like hairdressers). 

But hair dyes have also been linked to other cancers such as leukemia and lymphoma. Breast cancer has been linked to the use of both hair dye and straighteners/relaxers.

Most studies have looked at the risk for people who use hair dye for personal use. Others have evaluated the risk for people who work with hair dye as part of their job — like hairdressers and barbers. 

Let’s take a look at some of the research on hair dye and its links to specific types of cancer. 

Bladder cancer and hair dye

Hairdressers and barbers exposed to hair dye at work have an increased risk of bladder cancer. A recent, well-designed study that combined the results of 42 separate studies found that this risk was especially high in hairdressers who had worked for 10 years or more. 

Studies looking at the impact of personal hair dye use and bladder cancer haven’t shown such clear results. For example, one large study that combined the results of 17 smaller studies did not show an increased risk of bladder cancer in people who used hair dye. A smaller study that looked at about 1,500 people found that using permanent hair dye at least once a month increased the risk of bladder cancer. The risk increased even more in women who had used   permanent hair dye monthly for 15 years or more.

Breast cancer and hair dye 

Scientists have been studying a possible link between hair dye use and breast cancer for a long time. And the results of the data are mixed:

• Some data from a well-designed study that combined the results of 14 separate studies on this question didn’t show a link between hair dye and breast cancer. 

• But another study of more than 100,000 (mainly white) women showed a slightly higher risk of breast and ovarian cancers linked to longer personal use of hair dye. 

• Then, there is data from this study that combined the results of 14 similar studies, which linked hair dye to an increased risk of breast cancer in women regardless of race.

• Separately, a large study of women with a sister affected by breast cancer also linked hair dye and hair relaxer use to a higher risk of breast cancer. In this study, the risk was higher for Black women, especially if they used hair dye every 5 to 8 weeks. 

Leukemia or lymphoma and hair dye 

Certain blood cancers, like leukemia and lymphoma, have also been linked to hair dye. But again, the scientific evidence is mixed: 

• A 14-year study of almost 100,000 women did not find any links between hair dye use and the risk of getting leukemia or lymphoma. 

• But a newer study that combined data from 4 separate studies on 10,000 women found different results: Women who began coloring their hair before 1980 had a slightly increased risk of developing lymphoma compared to women who didn’t. This could be because some older hair dyes contained chemicals known to cause cancer. 

What types of hair dye have been associated with cancer risk?

Different types of hair dyes work differently. Permanent hair dyes (also called oxidative) are the most common — they constitute about 80% of all hair dyes. Both semipermanent and permanent hair dyes have been linked to cancer. 

• Temporary dyes: These cover the hair surface, but they don’t go into the hair shaft. They usually last for 1 to 2 washings.

• Semipermanent dyes: These stain the hair directly and usually last about 5 to 10 washings.

• Permanent hair dyes: These permanently change the hair shaft. They do this with different chemicals called “primary intermediates” and “couplers,” which form pigment when they’re exposed to hydrogen peroxide. Darker colors use higher amounts of intermediates. 

There aren’t specific dyes that cause cancer. But darker dyes have more chemicals that may be associated with cancer, so they may be a bigger concern.

Does DIY hair dye increase your cancer risk?

Yes. If you use semipermanent or permanent hair dyes, you’re exposed to chemicals that may be associated with an increased risk of cancer. 

What can you do to lower your risk of cancer when using hair dyes?

If you’re worried about the possible risk of using hair dye and developing cancer, here are some steps you can take:

• Use temporary hair dyes.

• Use hair dyes that have fewer potentially harmful chemicals.

• Color your hair less often or not at all (and embrace your gray).

• Follow directions when using semipermanent and permanent dyes (e.g., wear gloves and don’t use products longer than advised).

Why trust our experts?

Written by:

Maria Robinson, MD, MBA

Maria Robinson, MD, MBA, is a board-certified dermatologist and dermatopathologist who has practiced dermatology and dermatopathology for over 10 years across private practice, academic, and telehealth settings. She is a fellow of the American Academy of Dermatology and the American Society of Dermatopathology.

Edited by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. An experienced and dedicated pulmonologist and hospitalist, she spent a decade practicing and teaching clinical medicine at academic hospitals throughout London before transitioning to a career in health education and health technology.

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