Hair dye linked to breast cancer

The COVID-19 pandemic has seen the virus infect over 17.3 million people worldwide with more than 6.5 million cases still active and 675,000 fatalities. It has laid low the world’s economy – with record breaking drops in GDP and other economic measures. And unemployment is at levels which haven’t been seen in a hundred years.

None of this is good news. But at the same time, news coverage carries stories about people being worried about not being able to get their roots dyed.

Well, not to add misery to misery but a recent article in Chemical and Engineering News discusses a link researchers may have found between permanent hair dye and breast cancer.

To begin the discussion, let’s talk about what is actually involved in colouring hair. To do so, we need to understand the structure of hair. It is simply extruded protein – a lifeless strand composed of keratin. It is no more living tissue than our fingernails, or the horns, hooves, and feathers of other animals.

One of the common misconceptions about hair is it is some form of living tissue replete with DNA. It isn’t. Any DNA associated with hair is only found in the root cell. Each strand grows from a follicle or microscopic sack found beneath our skin. Each strand consists of a core called the ‘cortex’ which contains the colour components of the hair and a transparent covering called the ‘cuticle’.

A good analogy for a strand of hair is a transparent plastic straw. The straw is the cuticle and the empty interior is the cortex. If you use the straw to drink some orange juice, the straw will appear to turn orange. Use it to drink some Coca-Cola and it appears dark brown. For hair, the colour components in the cortex achieve the same effect. The structure of the compounds and their relative frequency or density in the cortex determine your hair colour.

Human hair is coloured by two pigments. Melanin is a dark brown or almost-black substance and phaeomelanin is a similar molecule but lighter in colour with a red-brown or yellow-brown tinge. The colour of a hair depends upon the amount and physical condition of these two pigments. Everything from blond to red to brown to black is determined by the amount and disposition of these two molecules.

If the follicle stops producing the pigments, then the cortex is no longer coloured and will become transparent. As the cuticle is also transparent, the loss of colour results in a translucent strand that shows up as either white or gray. There are some other factors involved, such as how rough the cuticle is, but empty hair is essentially colourless.

To dye gray hair, it is simply a matter of adding colour back into the cortex. To change hair colour, it is a little trickier as the first step involves removing the colour already present. There are many products on the market which are surface dyes. These colouring agents stick to the outside of the cuticle and will disappear with a few washings.

To produce permanent hair colouring, the dyes must pass through the cuticle and into the cortex. To do this, hair dyes strip the cortex and then add a mixture of compounds such as para-phenylenediamine and resorcinol. Then the chemistry happens. The molecules are oxidized, react with one another and link to form the final colouring agent which is now too large to diffuse back out through the cortex. In effect, hair dyes turn hairs into really tiny test tubes where interesting chemistry occurs.

All of the individual compounds used in hair dyes have undergone extensive screening for toxicity and carcinogenicity. Humans have been dying hair since 1907 and many tests have been performed on the compounds to verify their safety. The industry is diligent about meeting safety standards.

It was a bit surprising, then, when two recent studies – one by the US National Institute of Environmental Health Science called “the Sister Study” and the other by Adana Llanos of Rutgers School of Public Health – found a positive correlation between breast cancer and the use of permanent hair dyes. The Sister Study, for example, showed a 45 per cent higher risk of breast cancer for black women and a seven per cent higher risk for white women compared with study participants who did not colour their hair.

The caveat is the Sister Study included 46,000 women, aged 35 to 74, who have a sister who has or had breast cancer. There is already a genetic pre-disposition to breast cancer within the family and the dye may simply be activating the genes rather than causing the cancer. This is why the studies have revealed a correlation and not a causation.

As with most scientific questions, there is a lot more work to be done. But not being able to go to a hair salon during the COVID-19 pandemic for hair dyeing might turn out to be a good thing.