Today, hair dyeing has become a common practice for many. Young people use it to express individuality and showcase fashion, while middle-aged and older adults rely on it to appear more youthful. Simultaneously, media reports about hair dye causing cancer or damaging the liver and kidneys have never ceased. Which hair dyeing habits increase the risk of harm? What methods can reduce the damage from hair dyeing?
Hair dyeing may cause 4 types of harm
"Epidemiological statistics show that 50% of people dye their hair at least once or twice in their lifetime," said Liang Yanhua, Associate Professor of Dermatology at Southern Medical University's Southern Hospital and Associate Researcher at Yale University School of Medicine. The safety of hair dyeing is indeed crucial. Experts indicate that frequent hair dyeing may cause the following four major harms to the human body:
The most alarming harm: Potential carcinogenicity.Researchers at Yale University investigated women who began dyeing their hair before 1980 and found that over one-third developed lymphoma. Another study by the American Cancer Society involving 13,000 women who dyed their hair revealed a 3.8 times higher risk of leukemia compared to non-dyeing women.However, a 40-year Spanish study found that the cancer risk from hair dyes only slightly increased. Yang Shuxia, Associate Chief Physician at Peking University First Hospital's Dermatology Department, explained that while numerous international studies examine hair dye carcinogenicity, the definitive link remains controversial. Nevertheless, since the late 1970s, certain tumor-causing ingredients in hair dyes have been progressively phased out of formulations.
The most common harm: skin allergies. Yang Shuxia noted that p-phenylenediamine (PPD), a primary component in hair dyes, helps fix the color but is also a potent allergen. It can cause skin allergies in sensitive individuals, with contact dermatitis being the most common reaction.In EU countries like France and Germany, p-phenylenediamine has been explicitly banned from hair dyes. Yet in China, its use persists. Yang Shuxia emphasized that as long as hair dyes meet national standards and are used in appropriate amounts as directed, they remain safe.
The most hidden harm: damage to the liver and kidneys.Some products on the market add heavy metals like lead, mercury, and arsenic to enhance coloring effects. The lead content in certain products can be 5–10 times higher than that in paint. Long-term use causes chronic damage to the body, potentially leading to lead poisoning symptoms such as dizziness, limb numbness, and abdominal pain, as well as impairing the function of organs like the liver and kidneys.
The most embarrassing harm: Accelerated hair loss. Many suffer from hair loss precisely due to frequent dyeing. This occurs because certain benzene compounds like p-phenylenediamine in some dyes penetrate the cuticle—a vital component of hair—triggering oxidative reactions that lead to dryness, breakage, and even hair loss.
The most common hair dyeing mistake
Yang Shuxia notes that the harm caused by hair dyeing is closely linked to our dyeing habits. Factors like weather and color choice, seemingly unrelated, can actually amplify the risks.
Dyeing hair during smoggy days increases cancer risk.According to a February report in the authoritative scientific journal Materials, hair dyes contain harmful substances called secondary amines. While these act as dye fixatives to stabilize color, they can penetrate hair and skin, remaining there for weeks, months, or even years. They react with tobacco smoke or air pollutants to form potent carcinogens called nitrosamines. Therefore, dyeing hair during smoggy days may carry a higher cancer risk.
Dyes that are too dark or vibrant. Liang Yanhua noted that a recent U.S. study he reviewed indicates darker hair dyes may carry higher carcinogenic risks. Yang Shuxia added that generally, darker or more vivid dyes contain higher levels of p-phenylenediamine.Dyes containing p-phenylenediamine are favored for their longer-lasting effects but cause greater damage to hair and scalp. Semi-permanent or temporary dyes fade after 5–10 washes but inflict less damage. Combining dyeing with perming causes significant harm.Perming solutions often contain alkaline agents and oxidizing chemicals that strip the hair's protective outer layer, exposing its inner structure. This leads to yellowing, brittleness, loss of elasticity, and dullness. Applying dye to already damaged hair only compounds the damage. Dyeing hair when it's unsuitable. Yang Shuxia advises that the following five groups should avoid hair dyeing to prevent further harm:Those allergic to hair dye; 2. Individuals with damaged scalps, as toxic substances in dye are more readily absorbed into the body; 3. Elderly or frail individuals with impaired liver or kidney function, whose reduced detoxification capacity increases poisoning risks; 4. Pregnant or breastfeeding women; 5. Those with a family history of cancer, who face higher tumor risks and should minimize dyeing.