Does hair dye cause cancer? What is the difference between hair dyes that cost tens of dollars and hundreds of dollars?

When dyeing their hair, many people often look forward to the beauty brought by the new hair color, while smelling the pungent smell of hair dye and secretly worrying: Does hair dye have a carcinogenic risk?

Today we are here to talk to you about ~

01

Does hair dye cause cancer?

In fact, researchers began to study this issue as early as the 1960s:

In 1963, a study found that hairdressers were more susceptible to bladder cancer;

In 1971, British scholars proposed that hair dyes can increase women's chances of developing breast cancer.

In 1977, American scholars confirmed that hairdressers have a higher chance of developing lung cancer;

In 1978, experts reported that women who dyed their hair frequently had more chromosome breaks in their lymphocytes;

Since then, retrospective studies have found that the use of permanent hair dye increases the risk of bladder cancer, Hodgkin's disease, non-Hodgkin's lymphoma, leukemia, breast cancer, multiple myeloma, ovarian cancer, brain cancer, astrocytoma, brain tumors and other diseases.

But do hair dyes, especially permanent ones, really cause cancer?

This is not the case.

The above studies only say that hair dyes increase the risk of certain cancers, and other carcinogenic factors were not ruled out in the studies. Therefore, these studies cannot prove that hair dyes are positively correlated with the incidence of cancer.

The Journal of the American Medical Association (JAMA) published an article in 2005 stating that Professor Bahi Takkouche of the University of Santiago de Compostela in Spain and his collaborators conducted a meta-analysis of published studies and found that hair dyes did not increase the risk of bladder cancer or breast cancer.

In 2020, an article was published in the British Medical Journal (BMJ), one of the world's top medical journals.

This article, which followed 120,000 researchers for 36 years, showed that there was no significant correlation between personal use of permanent hair dyes and the risk of most cancers and cancer-related deaths. The study mentioned that even for those who dyed their hair more than 200 times in 36 years, no evidence was found that the use of hair dyes directly induced cancer.

As research deepens, some studies in recent years have shown that the correlation between hair dye and cancer cannot be confirmed.

02

Why are there concerns that hair dye causes cancer?

This is mainly because hair dye contains the substance "p-phenylenediamine".

p-Phenylenediamine, also known as Urs D, is an organic compound with the chemical formula C6H8N2. It is one of the simplest aromatic diamines and also an intermediate with wide applications.

Paraphenylenediamine reacts with oxygen to produce new colors. Paraphenylenediamine reacts with 3% hydrogen peroxide to produce black; it reacts with 5% ferric chloride to produce brown. At the same time, paraphenylenediamine has a strong affinity for keratin in hair, which allows it to better fix the color during the oxidation process, making the hair dyeing effect more lasting.

With the addition of p-phenylenediamine, hair dye has achieved a milestone success in color durability, but the presence of p-phenylenediamine has also caused people's health concerns - p-phenylenediamine is listed as a Class III carcinogen published by the 2017 edition of the World Health Organization's International Agency for Research on Cancer.

But its harm is not as great as we imagined.

According to the definition of the World Health Organization's International Agency for Research on Cancer, Class 3 carcinogens are "substances that cannot be classified by existing evidence, and the carcinogenicity evidence from animal and human studies is insufficient, or there is sufficient evidence from animal experiments but human studies have clearly shown that they have no carcinogenic effect, and they are substances that have been studied to have basically no carcinogenic hazard."

You will find that common items around us such as tea and coffee are actually on the list of Class III carcinogens.

List of carcinogens from the World Health Organization's International Agency for Research on Cancer. Image source: National Medical Products Administration

Therefore, there is no need to worry too much about the carcinogenicity of p-phenylenediamine.

Our country has strict requirements on 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, we have no need to worry about their carcinogenicity.

03

What’s the difference between a hair dye that costs dozens of dollars and a hair dye that costs hundreds of dollars?

There are many styles of hair dyes on the market, and the prices range from a few dozen to a few hundred yuan, but are the more expensive hair dyes better?

Actually 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 dye

Plant-based hair dye is a new type of hair dye under research and development, the main ingredients of which are natural plants or their extracts. However, it actually attaches the dye molecules directly to the surface of the hair, which is difficult to last long.

2. Metal salt hair dye

The main raw material is lead acetate. The advantage is good coloring and long-lasting color. 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.

3. Direct hair dye

Direct hair dyes can be divided into two types: temporary hair dyes and semi-permanent hair dyes.

The molecules of dyes used in temporary hair dyes are very large and will not penetrate into the hair fibers. They usually only temporarily adhere to the surface of the hair to achieve the coloring effect.

Unlike permanent hair dyes, the dyes used in semi-permanent hair dyes can penetrate the hair surface and directly dye the hair without undergoing oxidation.

The advantages of direct hair dyes are that they are safe and cause little damage to hair; the disadvantage is that the color does not last long.

4. Permanent (or oxidative) hair dye

Permanent hair dyes are generally chemically synthesized and consist of intermediates, coupling agents and oxidants. The main ingredients include: p-phenylenediamine and hydrogen peroxide

Permanent hair dyes mainly utilize the oxidative polymerization reaction of p-phenylenediamine to produce macromolecular pigments, thereby achieving the effect of dyeing and fixing the color.

The hair dye we have been discussing above is permanent hair dye. Permanent hair dye is the most widely used hair dye, accounting for about 80% of the market share.

When choosing hair dyes, you should pay attention to the product's ingredient list. Many products on the market that claim to be plant-based hair dyes often only add plant extracts to the hair dyes, and do not change the nature of the ingredients that contain p-phenylenediamine or even certain heavy metals. At the same time, some plant-based hair dyes contain complex and diverse plant ingredients, which can increase the risk of allergies.

It is worth mentioning that some of the “one-wash black” products that are now mainly promoted to the elderly are still hair dyes in essence.

These products may cause more harm than hair dye:

First, many "one-wash black" products are not produced by regular big brands. Most of the "one-wash black" products that claim to be shampoos have not obtained the approval number of special-purpose cosmetics ("national cosmetics special number"), 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 dye your 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. If you want to dye your hair safely, you should still pay attention to the following points:

1. Don’t dye and perm your hair at the same time

Hair dyes, especially permanent hair dyes, can damage hair during the coloring process, leaving it dry and frizzy. The chemicals used in perming often contain oxidants and alkaline substances, which are also extremely damaging to hair. If you perm and dye your hair at the same time, the damage to your hair will be multiplied. If time permits, it is recommended that you separate perming and dyeing to give your hair time to repair.

2. Do an allergy test before dyeing your hair

The hydrogen peroxide, chemical dyes, coupling colorants and other chemical ingredients contained in hair dyes, as well as the plant ingredients added to some hair dyes, are all allergens that are prone to allergic reactions and can easily cause scalp allergies during the hair dyeing process. Therefore, allergy tests must be done before dyeing your hair. You can dilute the hair dye with water and apply it to the inside of your elbow or behind your ear within 48-72 hours before dyeing your hair to observe whether there is an allergic reaction.

3. It is recommended not to wash your hair before dyeing

Because the oil secreted by the scalp can not only protect the scalp from damage by hair dye, but also make the hair color fuller.

4. Choose qualified hair dye

my country's "Regulations on the Supervision of Cosmetics Hygiene" clearly stipulates that hair dye products are one of the nine categories of special-purpose cosmetics, and they must obtain a special-purpose cosmetics approval number before they can be produced and sold. When choosing hair dyes, it is best to choose products produced by regular manufacturers, and pay special attention to whether there is a "national makeup special" logo on the product packaging box. Don't be superstitious about plant-based hair dyes that are very gimmicky.

Especially before going to the barber shop to dye your hair, remember to check the packaging of the hair dye with the barber to confirm whether it is a regular product.

5. Use hair dye products correctly according to the instructions

When using hair dye products, it is recommended to read the instructions carefully. Wear disposable gloves when using them to avoid direct contact with hair dye with your hands. It is not recommended to use hair dye when there is skin damage on the head, neck and hands. It is best to wait until the skin barrier is repaired before dyeing your hair.

6. Don’t dye your hair too frequently

It is recommended that the interval between each hair dyeing should be more than 4 months.

References:

[1] Wu Yan. Classification and analysis methods of hair dyes[J]. Occupation and Health, 2017, 33(16): 2287-2290. DOI: 10.13329/j.cnki.zyyjk.2017.0681.

[2] Wu Peihui. How to use hair dye to maximize benefits and avoid harm [J]. Capital Medicine, 2011, 18(08): 16-17.

[3] “Black laundering” was not approved [J]. Brand and Standardization, 2010(15):46.

[4] Yu Yanqiu, Wang Maozhong. Types of hair dyes and their harm to human body[J]. Enterprise Standardization, 2008(Z1):50-51.

[5] Xiao Ziying, Guangfeng. Aniline hair dyes and human health [J]. China Cosmetics (Industry), 2007(09):90-93.

[6]. Ministry of Health: There is currently insufficient evidence to infer that hair dyeing causes cancer in consumers [J]. Guangxi Quality Supervision Herald, 2006(03):11.

[7] Xiang Hongqin. Hair dyes do 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: Gaixin

Reviewer: Li Feng, Director of Dermatology Department, Union Hospital