But development of dyes in the last century or so

have included chemicals that may be carcinogenic,

that may cause cancer.

Watch to see what the science says about the risk.

"Do Hair Dyes Cause Cancer?"

Since there's typically no way to reverse hair color loss,

the use of hair colorants is a mainstay of management,

a practice documented as far back as 1500 BCE.

While gray hair may carry a distinguished look

and limit women's subjection to a sexualized gaze,

hair color constitutes a multibillion-dollar market

with up to 60 percent of men and women

in Western countries choosing to use coloring products,

many of which to cover gray.

For over a century, aromatic amines

have been the main chemicals used

in commercial permanent, oxidative hair dyes.

The primary problem with these compounds

is that they can be potent contact allergens.

Product labels often recommend a small 48-hour test application

to the skin before use,

but it can take up to a week for a skin allergy to flare up.

They also may cause cancer.

Hair products contain more than 5,000 chemicals,

and so it's hard to narrow it down,

but the aromatic amines, such as para-phenylenediamine,

that are often used in hair dyes

to prevent fading due to washing,

have been picked out as a "probable carcinogen."

Before industry reformulation

in response to mandated cancer warning labels,

9 out of 10 permanent hair dye products

were mutagenic,

meaning capable of causing DNA mutations.

This then appeared to translate into more than ten times

the odds of DNA damage in breast cells

obtained from the breast milk of women

who had used hair dye in the last six months,

compared to not using hair dyes at all.

But does it translate into more cancer?

A meta-analysis of 42 studies found that hairdressers,

particularly those who held their jobs

10 or more years, were at significantly higher risk

of developing bladder cancer later in life.

Hairdressers, beauticians, and barbers

may also suffer more lung cancer,

voice box cancer, and multiple myeloma.

There is some evidence that hairdressers may smoke more,

but the researchers took this into account.

They conclude that salons should be better ventilated,

that gloves should be used.

But how much is that going to help the person

whose head has been soaked in it?

Based on testing for radioactively-traced

hair dye ingredients in the urine,

experiments suggest that exposure to hair dye

may be several hundred-fold higher

in hair dye users than the occupational risk

to the hairdressers.

But thankfully there does not seem to be an excess risk

of bladder cancer among those who just

use hair dye personally.

Furthermore, major changes took place in the 1980s

to make hair dyes safer.

In 1979, the U.S. Food and Drug Administration

started requiring cancer warning labels

on hair dye products,

leading the industry to start reformulating to eliminate

the most carcinogenic ingredients.

A turning point in bladder cancer risk

isn't apparent from the data,

but this may just be a function of the long latency time

between exposure and malignancy for bladder cancer,

which can be 30 or 40 years.

If you look at faster developing cancers,

such as leukemia or follicular lymphoma,

there does seem to be a drop-off in risk after 1980,

though a 2019 meta-analysis, looking at

increased non-Hodgkin's lymphoma risk

without consideration of date range,

concluded "exposure to hair colorants should be reduced

as much as possible."

For prostate cancer, the doubling of odds

associated with hair dye use seems limited

to pre-1980 exposure,

and there appears to be no link to brain tumors

in either time frame.

As a tragically ironic aside,

while the risk associated with hair products may have declined

for white men and women, the opposite trend

seems to have occurred for certain hair products

targeted towards African Americans.

The Black Women's Health Study,

which assessed exposure in the 1990s,

found no association between breast cancer

and the use of hair "relaxers,"

chemical treatments used to straighten hair.

But in the early 2000s,

popular straighteners switched from

non-carcinogenic compounds, like lye,

to chemical cocktails containing formaldehyde.

So now, frequent straightener use

is associated with

about a 30 percent higher breast cancer risk.

Thankfully, there's been a shift towards embracing

more natural hair styles in the African-American community,

resulting in the sales of hair relaxers

falling by 40 percent in recent years.