When many people dye their hair, they often look forward to the beauty brought by the new hair color, while smelling the pungent smell of the hair dye, and are faintly worried: Does the hair dye have a risk of cancer?
Today we will talk to you about it~
01
Can hair dye cause cancer?
In fact, as early as the sixties of the last century, researchers began to study:
In 1963, a study found that hairdressers were prone to bladder cancer;
In 1971, British scholars proposed that hair dye can increase women's chances of breast cancer;
In 1977, American scholars confirmed that hairdressers have a higher chance of lung cancer;
In 1978, experts reported that women with frequent hair dyeing had more lymphocyte chromosomal breaks;
Since then, retrospective studies have found that the use of permanent hair dyes increases the risk of bladder cancer, Hodgkin's disease, non-Hodgkin lymphoma, leukemia, breast cancer, multiple myeloma, ovarian and brain cancer, astrocytoma, brain tumors, and more.
But can hair dyes, especially permanent ones, really cause cancer?
This is not the case.
These studies only say that hair dyes increase the risk of certain cancers, and other carcinogenic factors have not been ruled out in the studies, so these studies do not confirm a positive correlation between hair dyes and the development of cancer.
In a 2005 article published in the Journal of the American Medical Association (JAMA), Professor Bahi Takkouche of the University of Santiago de Composte and his collaborators conducted a mata-analysis of the published study and found that hair dyes did not increase the risk of bladder or breast cancer.
In 2020, the British Medical Journal (BMJ), one of the top medical journals in the world, published an article.
The paper's 36-year follow-up study of 120,000 researchers showed no significant correlation between individual use of permanent hair dye and the risk of most cancers and cancer-related death. The study mentioned that even those who were followed up with more than 200 hair dyes over a 36-year period found no evidence that the use of hair dye directly induced cancer.
As the research has deepened, some studies in recent years have shown that the association between hair dye and cancer cannot be proven.
02
Why is there a concern that "hair dye causes cancer"?
This is mainly because hair dyes contain the substance "p-phenylenediamine".
p-phenylenediamine ( p-phenylenediamine ) , also known as Uls D , is an organic compound with the formula C6H8N2 , one of the simplest aromatic diamines , and a widely used intermediate.
Structural formula for p-phenylenediamine. Image from the Internet
The reaction of p-phenylenediamine with oxygen produces a new color. When p-phenylenediamine reacts with a concentration of 3% hydrogen peroxide, it will appear black; Reaction with 5% concentration of ferric chloride can appear brown. At the same time, p-phenylenediamine has a strong affinity for keratin in hair, so that it can better fix the color during oxidation, making the effect of hair dyeing more durable.
With the blessing of p-phenylenediamine, hair dyes have achieved milestone success in color durability, but the presence of p-phenylenediamine has also raised health concerns - p-phenylenediamine is listed as one of the three categories of carcinogens published by the World Health Organization's International Agency for Research on Cancer in the 2017 edition.
But it's not as harmful as we think.
According to the definition of the World Health Organization's International Agency for Research on Cancer, Class 3 carcinogens are "substances that cannot be graded with available evidence, and the carcinogenic evidence in animal and population studies is insufficient, or the evidence in animal experiments is sufficient but the population study is clear that there is no carcinogenic effect, and it is a substance that has basically no carcinogenic harm after research." ”
You will find that common items such as tea and coffee are actually on the list of third class carcinogens.
List of carcinogens of the World Health Organization's International Agency for Research on Cancer. Image source: State Medical Products Administration
Therefore, there is no need to worry too much about the carcinogenicity of p-phenylenediamine.
Our country has strict requirements for the dosage of p-phenylenediamine in hair dyes: the maximum allowable concentration shall not exceed 6%. Therefore, for qualified hair dyes produced by regular manufacturers, there is no need to worry about their carcinogenicity.
03
Dozens of pieces and hundreds of hair dye
What's the difference?
There are various styles of hair dye on the market, and the price ranges from dozens to hundreds, but the higher the price point, the better?
It's not.
Hair dyes on the market can be roughly divided into four categories: plant-based hair dyes, metal salt hair dyes, direct hair dyes and permanent hair dyes.
1. Plant-based hair dyes
Plant-based hair dye is a new type of hair dye that is being researched and developed, and the main component is natural plants or their extracts. But it actually attaches dyeing molecules directly to the surface of the hair, which is difficult to last.
2. Metal salt hair dye
The main raw material is lead acetate. The advantages are good coloration and long color retention time. The disadvantage is that lead, as a harmful substance that can enter the human body, has been included in the list of banned substances in many countries.
Copyright images in the gallery are not authorized to be reproduced
3. Direct hair dye
Direct hair dye can be divided into: temporary hair dye and semi-permanent hair dye.
The dye used in temporary hair dye has large molecules, does not penetrate into the hair fiber, and usually only temporarily adheres to the surface of the hair to achieve the coloring effect.
Unlike permanent hair dye, the dye used in semi-permanent hair dye can enter the hair through the surface of the hair without oxidation.
The advantages of direct hair dye are safety and little damage to the hair; The disadvantage is the short color maintenance time.
4. Permanent (or oxidizing) hair dyes
Permanent hair dyes are generally chemically synthesized and consist of intermediaries, couplings and oxidants, and the main components include: p-phenylenediamine and hydrogen peroxide
Permanent hair dye mainly uses the oxidative polymerization reaction of p-phenylenediamine to produce macromolecular pigments, so as to achieve the effect of dyeing and fixation.
The hair dye we've been talking about above is a permanent hair dye. Permanent hair dye is the most widely used hair dye, accounting for about 80% of the market share.
When choosing a hair dye, pay attention to the ingredient list of the screening product. Many products on the market that claim their own plant hair dye often only add plant extracts to the hair dye, and do not change the essence of their own p-phenylenediamine, and even some heavy metal components. At the same time, some plant hair dyes add complex and diverse plant ingredients, which can also increase the risk of allergies.
Copyright images in the gallery are not authorized to be reproduced
It is worth mentioning that some of the "one-wash" products that are mainly targeted at elders are still hair dyes in essence.
These products can cause more harm than hair dyes:
First, many "one wash" products are not produced by regular big brands, and most of the "one wash" products that call themselves shampoos have not obtained the approval number of special-purpose cosmetics ("national makeup special characters"), and the product quality is worrying;
Second, these products often require a high frequency of use, and frequent use often increases the risk of allergies and physical damage.
04
How to color hair safely?
Although there is no definite positive correlation between hair dye and the incidence of cancer, some other harms of hair dye to the human body cannot be ignored. To color your hair safely, you should still pay attention to the following points:
1. Do not dye and perm your hair at the same time
Hair dyes, especially permanent ones, can damage hair during the coloring process, leaving hair dry and frizzy. The potions used in perms mostly contain oxidants and alkaline substances, which are also extremely damaging to the hair. If you perm and dye synchronously, the damage to hair quality is multiplied. If time permits, it is recommended to separate perm from coloring to give time for hair repair.
2. Do an allergy test before coloring your hair
Chemical components such as hydrogen peroxide, chemical dyes, coupled hair colorants contained in hair dye, as well as plant ingredients added to some hair dye, are allergens that are prone to allergic reactions and are easy to cause scalp allergies in the process of hair dyeing. Therefore, be sure to do an allergy test before dyeing your hair. The hair dye can be diluted with water within 48-72 hours before dyeing the hair and applied to the inside of the elbow or behind the ear to observe for allergic reactions.
A brand of hair dye recommends that consumers do an allergy test before use. Image source: A shopping website
3. It is recommended not to wash your hair before coloring your hair
Because the oil secreted by the scalp can not only protect the scalp from hair dye, but also make the hair coloration fuller.
4. To choose a qualified hair dye
The mainland's Regulations on Hygiene Supervision of Cosmetics clearly stipulate that hair dyeing products are one of the nine categories of special-purpose cosmetics, and must obtain an approval number for special-purpose cosmetics before they can be produced and sold. When choosing a hair dye, it is best to choose products produced by regular manufacturers, pay attention to whether there is a "national makeup special word" logo on the product packaging box, and do not superstitious plant hair dye with a large gimmick.
Especially before going to the barbershop to dye your hair, you must also remember to check the packaging of the hair dye with the barber to confirm whether it is a regular product.
5. Use hair coloring products correctly according to the instructions
When using hair coloring products, it is recommended to read the instructions carefully. Wear disposable gloves when using and avoid direct contact with hair dye. It is not recommended to use hair dye when there is skin damage on the head, neck and hands, and it is best to wait until the skin barrier is repaired.
6. Don't dye your hair too often
It is recommended to color each hair at an interval of more than 4 months.
Bibliography:
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[2] Wu Peihui. Capital Medicine,2011,18(08):16-17.)
[3] "One black wash" has not been approved[J].Brand and Standardization,2010(15):46.)
[4] YU Yanqiu,WANG Maozhong. The types of hair dye and its harm to human body[J].Enterprise Standardization,2008(Z1):50-51.)
[5] XIAO Ziying, GUANGFENG. Aniline hair dye and human health[J].China Cosmetics (Industry),2007(09):90-93.)
Guangxi Quality Supervision Herald,2006(03):11.)
[7] Xiang Hongqin. Hair dye does not increase the risk of bladder cancer or breast cancer[J].Foreign Medical Information,2005(10):14-15.)
[8] BMJ 2020; 370 doi: https://doi.org/10.1136/bmj.m2942 (Published 02 September 2020)
Author: Gai Xin
Review: Li Feng, Director of the Department of Dermatology, Union Medical College Hospital