Most of us don’t give much thought to the possible health risks of using hair dyes. They’re so ubiquitous – a third of women over age 18 color their hair, as well as about 10 percent of men over 40 – that we take their safety for granted. If these products were risky, we wouldn’t be able to buy them at every supermarket and corner drugstore – right?

Unfortunately, it’s not that simple. There are some 5,000 chemicals in today’s hair color products, and many of these ingredients have been around for decades – long before the FDA started keeping tabs. Because the use of hair dyes is so widespread, scientists have been trying for many years to sort out the ingredients to determine which, if any, are harmful to humans.

Early hair dye formulations contained chemicals known as aromatic amines that were found to cause cancer in animals. In the mid- to late 1970s, however, manufacturers changed the components in dye products to eliminate some of these components. Testing continues, and the results are often conflicting. Due to the very large number of chemicals in commercial hair dyes, variables in testing and differences in study designs, it can be extremely difficult to reach definitive conclusions.

There are three main types of hair dyes:

1. Temporary – these cover the surface of the hair but don’t penetrate into the hair shaft. They generally last for one to two washings.
2. Semi-permanent – penetrate the hair shaft and last for five to 10 washings.
3. Permanent (oxidative) – these 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.

Over the years, some studies have found an increased risk of bladder cancer among hairdressers and barbers. A 2008 report of the Working Group of the International Agency for Research on Cancer (IARC) concluded that some of the chemicals these workers are exposed to occupationally are “probably carcinogenic to humans.”

What about those of us who aren’t exposed to hair dye chemicals in the workplace, but only occasionally at home? Some studies have linked the personal use of hair dyes with increased risks of certain cancers of the blood and bone marrow, such as non-Hodgkin lymphoma (NHL) and leukemia; however, other studies have not shown such links. Studies of breast and bladder cancer have also produced conflicting results. Relatively few studies have been published about the association of hair dye use with the risk of other cancers. Based on its review of the evidence, IARC concluded that personal use of hair dyes is “not classifiable as to its carcinogenicity to humans.” In other words – they’re not drawing any conclusions either way … at least for now.

If you want to dye your hair but are concerned about safety, the FDA offers these suggestions:

• Consider delaying dyeing your hair until later in life when it starts to turn gray.
• Consider using henna, which is largely plant-based.
• 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 of the newer hair dye products are vegetable-based. From a results standpoint, these products may not be as effective; for example, they may fade sooner than conventional products or the desired shade may be a little off. However, for those who want a safer option, this may be the way to go.