Myth: Shampoo contains silicon, which can cause hair loss, alopecia and itchy scalp. Hair is smooth and smooth after washing, because chemical components such as silicon or dimethylsiloxane are added to shampoo, which is used to fill the gaps between hair scales, thus creating a smooth touch. The impermeability and other inertness of silicon itself will also close pores, which will make the scalp itch easily, and may even lead to hair loss and hair loss. Truth: Such remarks have been popular on the Internet for many years, and shredders have received many inquiries about this topic. When we say that shampoo contains "silicon", we don't actually mean that it contains silicon, but dimethyl silicone oil. (Dimethyl) silicone oil is a common name of polydimethylsiloxane (PDMS), which is liquid at room temperature, also known as "silicone". With the increase of polymerization degree, solid PDMS will appear. Regardless of their state, all PDMS are the same substance and have the same structure: the chemical structure of polydimethylsiloxane (PDMS), which determines that PDMS is an "inert" substance, that is, its chemical properties are very stable. Since 1950s, silicone oil has been tested in personal care products, but it can't get out. Since 1970s, PDMS has been living in shampoo and hair care products, taking away the elegance of vegetable oil, cetyl alcohol and other ingredients that have been used for thousands of years. Why should we use silicone oil? Hair is produced by hair follicles in the scalp, and the main component is keratin. Enlarge the hair, and the uneven hairs (hair scales) on it can be clearly seen, like fish scales. Shampooing is to remove dust and excess grease from hair and scalp, but water and anionic surfactants used for decontamination will cause a series of changes in hair: hair absorbs water, swells, moistens and softens, and grease usually attached to the outer layer of hair for lubrication and protection is washed away. If there are damaged and upturned hair scales, it will increase the friction between the hairs, which will lead to tangled hair when combing the hair, and mutual friction will aggravate the damage of the hair scales. That's not all. After the oil is removed by anionic surfactant, it is simply adsorbed on the hair. Wet negatively charged hair can at least stick together under the action of water, and when it dries, it will completely turn against each other, because the same sex repels each other. If you use a plastic comb to comb some static electricity, it will be lively and the static electricity problem caused by anionic surfactants can be easily solved. We just add some cations, such as quaternary ammonium salt, to the conditioner. But this still can't solve a series of hair quality problems caused by damaged hair scales. It is inevitable that you don't comb your hair-except for combing your hair, the chemical reagents used in dyeing, the high temperature and ultraviolet rays in the sun, which do great harm to your hair. At this time, grease comes in handy: lubrication reduces the chance of hair damage during combing. From the osmanthus oil on the dressing table of ancient girls to the conditioner put on the shelf decades ago, the protagonist is oil. The function of PDMS is to attach to hair, fill the damaged part of hair scales and make the hair surface smoother, which is also the "repair" function often mentioned in advertisements. Hair after "repair" is bright, easy to comb and firmer. [1] Hair without conditioner treatment is angular and the damaged parts are clearly visible; PDMS with smooth surface after treatment has another advantage: the formed protective layer can obviously keep the moisture content in the hair stable-compared with the hair with shampoo alone, the hair with conditioner can reduce the water loss under low humidity conditions and prevent the hair from excessively absorbing water under high humidity conditions. Too wet or too dry hair can cause difficulties in combing and hair style changes. Does silicone oil in toiletries affect the health of head skin? The hair care effect of PDMS is obvious to all, especially for long hair or hair dyeing, which is very harmful to hair scales. However, because it is attached to the hair to fill the damaged hair scales, some people have begun to worry about whether it will also deposit on the scalp, causing redness, inflammation, acne and hair loss. First of all, CIR experts believe that it is safe for cosmetics [2] and has no irritation to the skin. Although it can form a hydrophobic film on the skin, it is also breathable. In the process of searching the literature, I didn't find any information about acne, acne, hair loss and allergies. Instead, it is often used in products such as acne or oil-free. This is also its advantage over traditional oils and fats. We can retrieve a doctor's suspicion that PDMS may cause scalp pore blockage [3], but the doctor himself failed to provide reliable evidence to support his view. This is obviously not a mainstream view-there is still no literature report on pore plugging caused by PDMS. Most shampoos add a small amount of PDMS, hoping to achieve certain hair care effect while cleaning hair. But in fact, the hair care function of this kind of products is very limited (it is still very short-tempered after using hair! ), the possibility of remaining on the scalp to block pores is also very low. Because the content of PDMS added in shampoo is very small (below 1%), it is almost consumed under the action of cleaning surfactant and a lot of water. Hair conditioners and hair masks containing more silicone oil are always not recommended for scalp use, as long as they are applied to hair tips and above. First, it can reduce the dosage, second, the hair scales at the hair roots are less damaged, so it is unnecessary to use these products, and third, it can reduce the greasy feeling and heavy collapse feeling of the hair roots. In addition, the improvement of PDMS structure, such as etherification or adding amino group, can greatly improve the binding ability of silicone oil to hair and increase its water solubility. This kind of products can be attached to hair more effectively, while leaving less residue in other parts such as skin. Friends who have been troubled by the saying that silicone oil blocks pores should not worry too much. It should be noted that adding PDMS to shampoo products sometimes does have some minor disadvantages. For example, people with short hair rarely need hair care. If they choose products containing PDMS, they will bear additional costs, some of which are "uneconomical". In addition, because PDMS will be adsorbed on the hair, it will make the hair thicker and heavier, and at the same time reduce the static electricity between the hair, so the hair usually looks flat and not fluffy after drying. This is not a good phenomenon for people with soft hair [4]. In this case, we still have PDMS shampoo to choose from. Conclusion: PDMS can smooth hair scales and reduce hair friction injury, with obvious short-term or long-term benefits. On the contrary, it is speculated that its harm to scalp has not been confirmed.