It turns out that the so-called "bleach" is mostly highly toxic, and the most toxic component is mercury (mercury), and the principle of bleaching is to sink melanin in epidermis into dermis, rather than let melanin disappear. So whitening is only a superficial phenomenon. But the skin is constantly metabolized, so it won't be long before the skin color will become its original appearance again. If bleaching continues, melanin will sink again, and when melanin accumulates to a certain extent, it will turn black, making the skin darker than before. If this happens for a long time, it will make the skin suffer from "melanosis". Whitening at this time is not anti-disfigurement.
This is not the most serious consequence. If you use bleach in large quantities for a long time, the poison in alkali will damage your skin, bones, internal organs and even your brain!
Melanin in the skin is synthesized by melanocytes. In melanocytes, tyrosinase synthesizes tyrosine into a substance called dopa. "Dopa" reacts with cysteine to produce melanin. Therefore, tyrosinase is the most critical factor in melanin synthesis. Subsequently, melanin is transported to epidermal cells and piled up like bricks to protect DNA from ultraviolet rays. Ultraviolet light can activate the activity of tyrosinase and promote the synthesis of more melanin. Therefore, the synthesis of skin melanin is a self-protection mechanism of human body.
Tyrosinase is the key to synthesize melanin, so at present, most skin whitening products add tyrosinase inhibitors to cosmetics to destroy tyrosinase activity and achieve the purpose of reducing melanin.
Hydroquinone was once the most widely used whitening agent because of its low price and good effect. Later, it was found that it was induced leukemia. Since 200 1, the use of hydroquinone in cosmetics has been banned in Europe. In addition, there are some chemicals that can also inhibit tyrosinase, some of which need mercury as a catalyst. Cosmetic companies are also committed to finding all kinds of "pure natural" whitening agents. According to their research report, some plant extracts also have the effect of inhibiting tyrosinase activity.
"High-tech" is also used in whitening. In 2007, a French company developed a whitening product containing antisense oligonucleotides. According to the research papers of the company, whitening products containing antisense oligonucleotides can inhibit the expression of tyrosinase gene in skin cells, and the whitening effect can reach 30%. However, antisense oligonucleotides are generally not easy to enter cells. The real effect of this external application of "gene therapy" is questionable.
Usually, the content of tyrosinase inhibitor in whitening cosmetics for external use is limited, and the "bleaching" effect is limited and the duration is not long. On the other hand, oral tyrosinase inhibitors take effect slowly.
There is also a treatment called "chemical exfoliation", which can quickly remove melanin. Chemical exfoliation is to smear chemical reagents on the skin surface, corrode and exfoliate the skin, destroy the cells containing melanosome in the basement membrane of the skin, and make the skin thinner and whiter after regeneration.
Generally, α hydroxy acid (also called fruit acid, AHA) is used for mild peeling, and the effect is relatively mild. Fruit acid peels off the outermost stratum corneum of the skin, which has a certain effect on wrinkle removal and freckle removal. However, trichloroacetic acid (TCA) used for moderate exfoliation will corrode and destroy the skin in a short time, causing great trauma, so it needs the doctor's operation in clinic. Deep skin exfoliation is carried out with strong corrosive phenol reagent. If the whole face peels off, it usually takes 2 hours for external application, and the patient needs to take painkillers. Some patients even need ECG monitoring at the same time, because phenol is in danger of inducing arrhythmia and other complications.
The effect of mild and moderate peeling usually lasts only a few days to weeks, while the bleaching effect of deep peeling can last for months or even years. However, phenol used in deep stripping is a highly toxic chemical and carcinogen.
There are also some physical methods to exfoliate skin, such as laser and cryosurgery. But they are generally only suitable for removing spots and moles, and wounds sometimes leave scars.