Millions of people around the world color their hair every year, whether to cover grey strands or change their appearance. However, questions have lingered for decades about whether chemicals in hair dyes could increase the risk of cancer. Researchers have examined this issue closely, producing a large but sometimes mixed body of evidence. Here is what current research shows, and what health experts say it means for everyday users.

Understanding the Different Types of Hair Dyes

Hair dyes are not all the same. Their chemical composition and how they interact with hair vary widely, and this affects how scientists assess potential risks.

Temporary hair dyes coat the outside of the hair shaft and do not penetrate deeply. They usually wash out after one or two shampoos.

Semi-permanent dyes penetrate the hair shaft but do not permanently alter its structure. Their color typically lasts through five to ten washes.

Permanent dyes, also known as oxidative dyes, cause lasting chemical changes inside the hair shaft. These products remain popular because the color lasts until new hair grows in. They often contain colorless chemicals such as aromatic amines and phenols, which react with hydrogen peroxide to form permanent color. Darker shades generally rely on higher concentrations of these agents.

According to researchers, most cancer-related concerns focus on semi-permanent and permanent dyes, especially darker formulations that contain larger amounts of certain chemicals.

How People Are Exposed

When hair is dyed at home or in salons, small amounts of chemicals can be absorbed through the skin or inhaled from fumes. For most people, exposure is occasional. However, hairdressers, stylists, and barbers face repeated exposure over many years as part of their work.

Because of this, much of the scientific concern has centered on people who handle hair dyes professionally rather than individuals who use them occasionally.

Do Hair Dyes Cause Cancer?

Scientists have studied a possible link between hair dye use and cancer for many years. Research has focused most heavily on bladder cancer, blood-related cancers such as leukemia and lymphoma, and breast cancer.

To evaluate cancer risk, researchers rely on two main approaches: laboratory studies and population-based studies in people. According to cancer experts, neither approach alone is enough to draw firm conclusions, so both are considered together.

Studying hair dyes is particularly challenging. Products can contain thousands of different chemicals, and formulations have changed significantly over time. In the late 1970s, some aromatic amines used in early hair dyes were found to cause cancer in laboratory animals. Manufacturers later modified or removed many of these ingredients. As a result, scientists often distinguish between hair dye use before and after 1980 when analyzing long-term risks.

What Laboratory Studies Show

Laboratory experiments have shown that some chemicals used in hair dyes can cause cancer in animals, especially when given in large doses over long periods. While studies confirm that some dye ingredients can be absorbed through the skin, most lab research has not shown a clear increase in cancer risk from skin application alone.

Experts caution that results from animal studies do not always translate directly to real-world human exposure.

Evidence From Studies in People

Epidemiological studies have produced mixed findings, depending on the type of cancer and the population studied.

For bladder cancer, research involving hairdressers and barbers has found a small but fairly consistent increase in risk. In contrast, studies of people who dye their own hair have not shown a consistent link.

When it comes to leukemia and non-Hodgkin lymphoma, results vary. Some studies report a higher risk of certain subtypes among women who used hair dyes, particularly darker colors or products used before 1980. Other studies, however, have found no increased risk.

Breast cancer research has also been inconclusive. Many studies show no association with hair dye use, while some more recent research suggests a possible link with certain subtypes of breast cancer but not others.

For other cancers, there is not enough evidence to draw firm conclusions.

According to health researchers, the widespread use of hair dyes makes continued study important, especially to clarify long-term risks and the impact of newer formulations.

What Expert Agencies Say

International and national health agencies regularly review the available evidence on cancer risks.

The International Agency for Research on Cancer, which is part of the World Health Organization, has concluded that occupational exposure as a hairdresser or barber is probably carcinogenic to humans, based mainly on bladder cancer data. However, IARC considers personal use of hair dye not classifiable as to its carcinogenicity due to insufficient evidence.

The United States National Toxicology Program has not classified hair dyes as a whole. Still, it lists some chemicals that are or were used in hair dyes as reasonably anticipated to be human carcinogens.

According to the American Cancer Society, these classifications reflect uncertainty rather than proof of harm for personal users.

Regulation of Hair Dyes

In the United States, hair dyes fall under the regulation of the Food and Drug Administration as cosmetic products. By law, manufacturers are responsible for ensuring product safety. The FDA does not approve individual ingredients before products reach the market.

If a cosmetic product is found to be unsafe or mislabeled, the FDA can request a recall and take legal action if necessary. However, many older hair dye ingredients were exempted from early regulatory authority in the 1930s, and some remain in use today.

Should People Limit Their Use?

So far, most studies have not shown a strong or consistent link between personal hair dye use and cancer. Still, experts say more research is needed.

There are no specific medical guidelines advising people to stop using hair dye. General cancer prevention advice, such as not smoking, eating a balanced diet, staying physically active, and attending routine health screenings, remains far more important. Smoking, in particular, is a known risk factor for bladder cancer and certain leukemias.

Some individuals may still choose to limit exposure for other reasons. Hair dyes can trigger severe allergic reactions in some people and may cause hair damage or loss. Some doctors also advise women to avoid hair dye during pregnancy, especially in the first trimester, as a precaution due to limited data.

For those who continue to use hair dye, the FDA recommends following safety instructions carefully. This includes performing a patch test before every use, wearing gloves, rinsing the scalp thoroughly after application, and never using hair dye on eyebrows or eyelashes. Hair should not be dyed if the scalp is irritated or damaged.

Vegetable-based dyes are another option for people concerned about chemical exposure, although they may fade faster or offer less dramatic color changes.

The Bottom Line

According to reports from cancer research agencies, occasional personal use of modern hair dyes has not been clearly linked to cancer. However, occupational exposure appears to carry higher risk, and unanswered questions remain. As scientists continue to study newer formulations, experts recommend informed choices, proper use, and attention to overall health as the most practical approach.