Many American women, as well as a small but increasing number of men, use hair dyes. You may have heard rumors about a link between using hair dye and getting cancer. Many studies have looked at hair dyes as a possible risk factor for various types of cancer. Here we will discuss what the research shows so that you can make choices that are comfortable for you.
Types of hair dyes
Hair dyes vary greatly in their chemical make-up. People are exposed to the chemicals through skin contact. There are 3 main types of hair dye:
Temporary hair dyes
Temporary dyes cover the surface of the hair but do not penetrate into the hair shaft. They generally last for 1 to 2 washings.
Semi-permanent hair dyes
Semi-permanent dyes do penetrate into the hair shaft. They typically last for 5 to 10 washings.
Permanent (oxidative) hair dyes
Permanent dyes cause lasting chemical changes in the hair shaft. They are the most popular types of hair dyes, because the color changes last until the hair is replaced by new growth. They are sometimes referred to as coal-tar dyes because of some of the ingredients they contain. Permanent dyes contain various colorless substances such as aromatic amines and phenols. In the presence of hydrogen peroxide, these substances go through a chemical reaction to become a dye. Darker hair dyes tend to use higher concentrations of coloring agents.
Concern about cancer risk is largely limited to the semi-permanent dyes and the permanent dyes. Because darker dyes have higher concentrations of some chemicals that may cause cancer, these products are of greatest potential concern.
Do hair dyes cause cancer?
Researchers use 2 main types of studies to try to determine if a substance or exposure causes cancer. (A substance that causes cancer or helps cancer grow is called a carcinogen.)
In studies done in the lab, animals are exposed to a substance (often in very large doses) to see if it causes tumors or other health problems. It's not always clear if the results from these types of studies will apply to humans, but lab studies are the best way to detect the potential for a substance to cause cancer in humans before widespread exposure occurs.
Another type of study looks at cancer rates in different groups of people. Such a study might compare the cancer rate in a group exposed to a substance versus the rate in a group not exposed to it, or compare it to what the expected cancer rate would be in the general population. But studies in people can sometimes be hard to interpret, because there may be other factors affecting the results that are hard to account for.
In most cases neither type of study provides definitive evidence on its own, so researchers usually look at both human and lab-based studies.
Studying something like hair dyes can be even more complicated because they may contain any of thousands of different chemicals. On top of this, the ingredients in hair dyes have changed over the years. Early hair dyes contained chemicals, including some aromatic amines, which were found in the late 1970s to cause cancer in lab animals, so hair dye manufacturers changed some of the chemicals in their products. Studying exposure to hair dyes from decades ago may not be the same as studying current exposures. In fact, many studies classify personal hair dye use based on whether it took place before or after 1980.
Studies done in the lab
Some of the ingredients used in hair dyes (including certain aromatic amines) have been shown to cause cancer in lab animals, usually when the animals were fed large amounts of the dyes over a long period of time. Although studies have shown that some of the dye applied to an animal's skin is absorbed into the bloodstream, most have not found a link between skin application and cancer risk. It is not clear how these results might relate to people's use of hair dyes.
Studies in people
Most of the studies looking at whether hair dye products increase the risk of cancer have focused on certain cancers such as non-Hodgkin lymphoma, leukemia, bladder cancer, and breast cancer. These studies have looked at 2 groups of people:
- People who use hair dyes regularly
- People who may be exposed to them at work
Most studies of people exposed to hair dyes at work, such as hairdressers and barbers, have found a small but fairly consistent increased risk of bladder cancer. However, studies looking at people who have their hair dyed have not found a consistent increase in bladder cancer risk.
Studies looking at a possible link between personal hair dye use and the risk of blood-related cancers such as leukemia and lymphoma have had mixed results. For example, some studies have found an increased risk of certain types of non-Hodgkin lymphoma (but not others) in women who use hair dyes, especially if they began use before 1980 and/or use darker colors. The same types of results have been found in some studies of leukemia risk. However, other studies have not found an increased risk. If there is an effect of hair dye use on blood-related cancers, it is likely to be small.
Most studies looking at hair dye use and breast cancer have not found an increased risk. For other types of cancer, too few studies have been done to be able to draw any firm conclusions.
Many people use hair dyes, so it is important that more studies are done to get a better idea if these dyes affect cancer risk.
What expert agencies say
Several agencies (national and international) study different substances in the environment to determine if they can cause cancer. The American Cancer Society looks to these organizations to evaluate the risks based on evidence from laboratory, animal, and human research studies.
Some of these expert agencies have classified hair dyes or their ingredients as to whether they can cause cancer.
The International Agency for Research on Cancer (IARC) is part of the World Health Organization (WHO). Its major goal is to identify causes of cancer. Based on the data regarding bladder cancer, IARC has concluded that workplace exposure as a hairdresser or barber is "probably carcinogenic to humans." However, the IARC considers personal hair dye use to be "not classifiable as to its carcinogenicity to humans," based on a lack of evidence from studies in people.
The National Toxicology Program (NTP) is formed from parts of several different US government agencies, including the National Institutes of Health (NIH), the Centers for Disease Control and Prevention (CDC), and the Food and Drug Administration (FDA). The NTP has not classified exposure to hair dyes as to its potential to cause cancer. However, it has classified some chemicals that are or were used in hair dyes, such as 4-chloro-o-phenylenediamine, as "reasonably anticipated to be human carcinogens."
(For more information on the classification systems used by these agencies, see our document, Known and Probable Human Carcinogens.)
Do hair dyes cause any other health problems?
Some of the ingredients in hair dyes can cause allergic reactions leading to severe skin and eye irritation in some people. Eye irritation can seriously affect vision and, very rarely, lead to blindness. Hair dyes can also actually cause hair loss in some people.
For these reasons, it is recommended that users test these products on a small area of skin before using them on their hair and scalp. It is also for these reasons that these products should not be used to dye eyebrows.
Are hair dyes regulated?
The Food and Drug Administration (FDA) is responsible for regulating the safety of cosmetics in the United States. The FDA can prevent the sale of any cosmetics found to be harmful. This includes any new ingredients to be used in hair dyes. However, many of the older ingredients in hair dyes (some of which are still in use) were excluded when the FDA was initially given the power to regulate these products back in the 1930s.
Should I limit my exposure to hair dye?
It is not clear how much personal hair dye use might raise cancer risk, if at all. Most studies done thus far have not found a strong link, but further studies are needed to help clarify this issue.
Other than recommendations that apply to everyone (having routine screening exams, eating a healthy diet, being physically active, etc.), there is no specific medical advice for current or former hair dye users. Smoking is a known risk factor for bladder cancer and some types of leukemia (as well as many other cancers and other diseases), and quitting smoking can improve your health, regardless of whether or not you use hair dyes.
For people who want to dye their hair but are concerned about safety, the FDA has provided some suggestions:
- Consider delaying dyeing your hair until later in life when it starts to turn gray.
- Consider using henna, which is largely plant-based.
- Be sure to do a patch test for allergic reactions before putting the dye in your hair. Do a patch test before every use.
- Carefully follow the directions on the hair dye package.
- Wear gloves when applying hair dye.
- Don't leave the dye on your head any longer than necessary.
- Rinse your scalp thoroughly with water after use.
- Never mix different hair dye products, because you may cause potentially harmful reactions.
- Never dye your eyebrows or eyelashes.
Some newer hair dye products are vegetable based. These products may have some drawbacks, such as not being able to change hair color drastically or having the color fade sooner than is seen with permanent dyes (unless they contain some of the same ingredients as the permanent dyes). But they may be another option for some people concerned about hair dye safety.
More information from your American Cancer Society
We have some related information that may also be helpful to you. These materials may be ordered from our toll-free number, 1-800-227-2345.
National organizations and Web sites
In addition to the American Cancer Society, other sources of information and support include*:
National Cancer Institute (NCI)
Toll-free number: 1-800-422-6237 (1-800-4-CANCER)
Web site: www.cancer.gov
Hair dyes and cancer: www.cancer.gov/cancertopics/factsheet/Risk/hair-dyes
No matter who you are, we can help. Contact us anytime, day or night, for information and support. Call us at 1-800-227-2345 or visit www.cancer.org.
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Last Revised: 02/17/2011