Are you thinking of dyeing your hair? 5 reasons to reconsider

Author: Zhang Like, Professor at Capital Medical University.

As the year-end approaches, hair dyeing becomes increasingly popular. However, individuals with sensitive skin, existing injuries, or pregnant women should undergo allergy testing before using hair dye.

Hair dye consists of various ingredients, typically including: 1. Coloring Agents: These are the main ingredients responsible for the dye’s color, derived from either natural sources or synthetic chemicals. 2. Developers: Often containing hydrogen peroxide, these substances activate the coloring agents and allow the dye to penetrate the hair shaft. 3. Ammonia or Ammonia Substitutes: These chemicals open the hair cuticle for better dye infiltration. 4. Conditioning Agents: Ingredients such as oils and silicones that help protect the hair and reduce damage during the dyeing process. 5. Fragrance: Added to provide a pleasant scent, although some individuals may be sensitive to these additives. 6. Preservatives: Ensure ongoing effectiveness and safety of the product. 7. Thickeners and Stabilizers: These ingredients maintain the consistency and stability of the dye formulation.

The most widely used type of hair dye is permanent hair color.

Hair dye can be classified into three categories: temporary hair dye, semi-permanent hair dye, and permanent hair dye.

Temporary hair dye particles are relatively large and cannot penetrate the skin to reach the hair roots. They adhere to the hair surface, creating a colored coating layer. Exposure to water causes these dyes to fade quickly, making them suitable for short-term styling. They are commonly available as sprays or hair waxes and typically cause minimal scalp irritation.

Semi-permanent hair dyes utilize alkaline disperse dyes with smaller molecules that exhibit a strong affinity for hair, allowing partial penetration of the hair strands. The color lasts for a few weeks, develops pigments through an oxidation reaction, and does not require hydrogen peroxide, resulting in relatively low damage to hair quality.

3. Permanent hair dye offers the longest-lasting color post-application. It usually consists of two tubes, A and B, where Tube A contains dye intermediates and Tube B contains the oxidizing agent. When mixed and applied to the hair, they undergo a chemical reaction to form large molecular pigments.

Certain ingredients in hair dye can trigger allergies in individuals.

Para-phenylenediamine is classified as an aromatic amine.

It is a primary cause of allergic reactions associated with hair dye.

Para-phenylenediamine, or Ursol D, is an organic compound with the chemical formula C6H8N2. As one of the simplest aromatic diamines, it is a widely used intermediate in various applications.

Source: College of Life Sciences, Jilin University.

Para-phenylenediamine undergoes a reaction with oxygen to produce different colors. When it reacts with 3% hydrogen peroxide, it appears black, and with 5% ferric chloride, it turns brown. Moreover, para-phenylenediamine binds strongly to keratin in hair, enhancing color retention during the oxidation process and ensuring a longer-lasting hair dye effect.

Dyeing methods utilizing para-phenylenediamine and its derivatives.

Source: China Food and Drug Administration Website.

Contact with para-phenylenediamine can result in inflammation of the eyes, skin, and respiratory tract, including the throat. It can also lead to allergic reactions affecting the skin and respiratory system, often manifesting as redness and itching on the scalp and face/neck area. In more severe instances, blisters, oozing, periorbital edema, and intense itching may occur based on erythema. In extreme cases, systemic allergic reactions may develop.

Does hair dye really cause cancer?

Para-phenylenediamine is classified as a Group 3 carcinogen.

However, the evidence regarding its carcinogenic effects in humans remains unclear.

According to the International Agency for Research on Cancer of the World Health Organization, Group 3 carcinogens are defined as "substances for which there is insufficient evidence to classify them. Although there may be sufficient evidence from animal studies, human studies do not demonstrate a clear carcinogenic effect. These substances present minimal carcinogenic risk based on research findings."

The International Agency for Research on Cancer maintains a list of carcinogens, which includes substances such as tea and coffee.

Source: National Medical Products Administration.

The link between hair dyeing and perming practices and cancer risk varies based on individual differences, the quality of dye and perm agents, and the frequency of treatments. In our country, strict regulations govern the amount of para-phenylenediamine present in hair dye products. As stated in GB7916-1987 "Cosmetic Hygiene Standards," the maximum permissible concentration must not exceed 6%.

Certain individuals should avoid casual hair dyeing.

Individuals allergic to hair dye.

Chemical components and some plant ingredients in hair dye can act as allergens triggering allergic reactions. Therefore, individuals with sensitive skin should conduct an allergy test before dyeing their hair. They can dilute the dye with water and apply it to the inner elbow or behind the ear 48 to 72 hours prior to dyeing and monitor for any allergic reactions.

Individuals with scalp injuries.

If you have skin lesions, such as eczema or ulcers, or suffer from a skin disease, dyeing hair may introduce a significant amount of toxic substances from the dye into the body.

Elderly individuals who are frail and have liver or kidney dysfunction.

Such individuals may have weak immune systems, and older adults often exhibit more gray hair. Compared to healthy black hair, gray hair lacks pigment and has tightly closed cuticles, making it difficult for synthetic pigments to penetrate. Most hair dye products designed for gray hair contain a higher pigment concentration.

Source: Dingxiang Life Research.

To ensure that pigments penetrate effectively and deposit onto the hair, formulas often include significant amounts of ammonia to open the cuticles, which can adversely affect health.

Pregnant and breastfeeding women.

Pregnant women typically have more sensitive bodies, making them more prone to allergic reactions.