In fact, dyeing hair is not a patent of modern people. Human hair dyeing has a long history, even dating back to BC 1000 years.
The ancient Egyptians had known to use hot water to extract foam anthocyanins to dye hair orange; The Germans in ancient Europe would mix sheep fat with plant ash juice and dye their white hair black; The Romans dyed their hair with sappan, madder and purple velvet; In the earliest drug monograph "Shen Nong Ben Cao Jing" in the Eastern Han Dynasty in China, some plants that can blacken white hair, such as Artemisia annua, can "blacken hair". Ge Hong, a medical scientist in the Eastern Jin Dynasty, recorded in "Elbow Backup Emergency Prescription" that dyeing hair with vinegar-boiled soybeans can have the effect of "white hair and beard" and "black as paint".
The discovery and synthesis of aniline violet dye by W.H.Perkin in England made it possible to dye hair with stable performance and lasting coloring. The main component of hair dye, p-phenylenediamine (PPD), was successfully synthesized, but it was mainly used as an industrial dye at that time. It was not until 1883 that the French company Monnet developed p-phenylenediamine chemical hair dye, and the hair dye entered the era of rapid development.
What happened to the hair after it was dyed? What effect does dyeing hair have on hair quality?
To know how hair is dyed, we must first understand the composition and structure of hair. In the previous perm article (link/yrhcz/yrhcz _ zpzs/yrh _ 2020/202003/t2020031_ 484676.html), the hair is divided into two parts, the hair follicle is buried in the scalp, and the hair follicle is exposed daily.
Hair shaft consists of medulla, cortex and stratum corneum from inside to outside. The medulla is located in the center of the hair shaft and consists of 2 ~ 3 layers of polygonal keratinocytes.
The cortex closely surrounds the medulla, and the cortical cells are about 2 μ m to 3 μ m in diameter. The cortical cells are composed of many coarse fibers, fine fibers and fibrils. The fibrils are composed of 2 ~ 3 strands of α -helix keratin. Many fibrils form small fibers with a diameter of 8 10-3μm, and then many small fibers form large fibers. These fibers are embedded in the cell matrix composed of high sulfur protein, forming a very compact fiber bundle. The matrix of cortical cells contains pigment particles, which determine our initial hair color.
Hair scales (cuticle) are at the outermost layer of hair shaft, and there are 3 ~ 7 layers of cuticle around hair shaft. Hair scales and hair cortex are rich in high-sulfur proteins, and disulfide bonds, hydrogen bonds and salt bonds formed between amino acids make hair have quite strong tensile properties, which can stably maintain a straight or curly shape.
Lipid is also an important component of hair, which is mainly located in the intercellular spaces between hair cuticle cells and between hair cuticle and cortical cells, and is called cell membrane complex (CMC). The combination of CMC lipids and protein can form lipoproteins, which form a continuous network structure around hair fibers and play an adhesive role between cells.
Knowing the structure of hair, let's take a look at which part of hair color the hair dye changes.
Different hair dyes have different hair dyeing principles. Hair dyes can be divided into three categories according to dye components: inorganic hair dyes (metal hair dyes), synthetic hair dyes (oxidized hair dyes) and plant hair dyes (natural hair dyes).
Inorganic hair dye: a compound dye containing metal salts such as lead, silver, iron and copper. The mechanism of action is that metal ions in hair dye penetrate into hair and react with sulfur in cysteine in hair protein to produce black lead sulfide and silver sulfide, thus dyeing hair black. The ancient Greeks used lead-lined water pipes, and running water slowly dissolved lead. People who often wash their hair with this water have dark hair, but heavy metal lead ions are easy to accumulate in the human body and cause poisoning. At present, the use of this hair dye has basically become history.
Synthetic hair dye: it is also widely used in the market at present. There are many forms such as paste, liquid, powder and bubble, which can be divided into temporary hair dye, semi-permanent hair dye and permanent hair dye according to color persistence.
Temporary hair dyes, generally made of water-soluble macromolecular dyes, cannot penetrate into the cortex and can only be attached to hair scales. Temporary hair dyes are mostly spray-like products, which are generally used for performances, makeup and so on. If you wash it once, it will be removed. Because they are attached to the hair surface, the damage to the hair will be less.
Semi-permanent hair dye, the dye molecule is small, and the main dyes are nitrobenzene diamine, nitrophenol and azo acid dyes. These ingredients can penetrate into the hair surface and partially enter the cortex. After dyeing, it is more washable than temporary hair dye, and the color will fade after 6- 12 washing. The action mechanism of this hair dye is mainly to make the color deposit on the surface and cortex, so it is less irritating.
Permanent hair dyes are mostly composed of two preparations, which are generally packaged in two bottles, one bottle of dye matrix and one bottle of oxidant matrix, which need to be mixed before dyeing. The first agent is a dye, mainly an oxidation dye intermediate (such as p-phenylenediamine), and also contains an alkalizing agent and a coupling agent (such as hydroquinone). The second agent is an oxidant, and the main component is hydrogen peroxide, which is hydrogen peroxide.
When dyeing hair, the alkaline substances in the hair dye will cause the hair to swell. The dye intermediate in the first dose is a small molecule with low viscosity and easy flow, and the hydrogen peroxide in the second dose can penetrate into the hair cortical fibers, and the melanin inherent in the hair is oxidized and decolored by the hydrogen peroxide. Dye intermediates and coupling agents condense under oxidation to form stable colored dye molecules, which can color hair. Because of the large molecular weight of colored substances, it is not easy to pass through hair gaps, so it has high washing fastness and the color can last for 1 ~ 3 months, so the permanent hair dye will not keep the color permanently after dyeing once.