Ultraviolet rays in sunlight can kill or inhibit bacteria on the surface of the skin, promote the conversion of dehydrocholesterol in the skin into vitamin D9, and can also enhance the body's disease resistance, promote the body's metabolism, and have a positive impact on the growth of the human body. Development plays an important role. On the other hand, ultraviolet rays are harmful to human skin and hair. Ultraviolet radiation (uV) can cause skin burns and erythema. Promote premature aging of the skin, cause keratitis and cataracts, damage immune cells in the skin, and cause systemic immune function suppression. With the increasing popularity of refrigeration equipment such as refrigerators and air conditioners, the leakage of Freon (cFc) in compressors is also increasing, which intensifies the hole in the ozone layer. The intensity of ultraviolet radiation received by the ground tends to increase. Therefore, the research on ultraviolet rays, sunscreen agents and their products has also attracted the attention of many scholars.

1 Ultraviolet rays and their effects on the human body

1.1 Ultraviolet rays

Sunlight consists of many wavelengths of the electromagnetic spectrum. When sunlight penetrates the Earth's atmosphere, some wavelengths of light are filtered out, and the remaining radiation reaches the Earth's surface as ultraviolet and infrared light. UV rays interact with skin cells and cause a wide range of damaging effects, see Table 1.

1.2 Damage of ultraviolet rays to skin

UVR is an immunosuppressive factor, and damage to immune function may lead to the occurrence of skin tumors. Toewa et al. first observed that ultraviolet radiation changed the function of antigen-presenting cells (APC)-Langerhans cells (Lc). In normal skin tissue, Lc forms a network structure in the epidermis. One of its functions is to absorb foreign antigens, travel to local lymph nodes, and present the antigens to T cells. Ultraviolet radiation changes the morphology of Lc in the epidermis, destroys the network structure, reduces the amount of Lc, and changes its function. The increase in inflammatory cells leads to immune tolerance. In addition, uridylic acid is the deamination product of histidine and is abundant in the upper layer of the epidermis. After UV irradiation, it changes from the trans structure to the cis structure thereby inhibiting the function of T cells. Several laboratories have confirmed the immunosuppressive effects of uridylic acid.

The impact of ultraviolet radiation on the skin is also reflected in the photoaging of the skin. People who are overexposed to the sun will look very old, and various vegetations will grow on the photo-aged skin. Deep wrinkles appear, the skin is sagging and saggy, and there are many pigment spots. These phenomena reflect changes in skin structure but are completely different from physiological aging changes. UVB can cause skin erythema, DNA damage and skin tumors. The research results of Sams et al. suggest that UVB can damage connective tissue. They irradiated hairy mice with 30-50 times the minimum erythema dose of UVB, and the result was moderate elastic fiber hyperplasia. After long-term chronic irradiation, the decomposition rate of collagen is greater than the cell synthesis capacity. As a result, the dermis becomes thinner, atrophic and causes visible skin photoaging. Exposure to uVA irradiation can produce erythema and vascular damage. Although the density of elastic fiber deposition is lower than the effect of UVB, the degeneration of elastic fibers can extend deep into the dermis, which is very harmful to people's skin.

1.3 Damage of ultraviolet rays to hair

In addition to affecting the skin, ultraviolet rays also cause hair damage. When hair is exposed to large doses of UV rays. Hair can change color and brown hair tends to fade. Blond hair and red hair turn yellow. This is due to the bleaching effect of photooxidation and photodegradation of amino acids - cystine, tyrosine, tryptophan. Amino acid photodegradation also causes a reduction in hair tone. The most direct way to protect your skin and hair from UV rays is to cover them with clothing, a hat or an umbrella. In addition, scientists have discovered various substances that absorb or block ultraviolet radiation through research.

2 Sunscreen in the field of cosmetic crystals

2.1 Sunscreen agents

At present, sunscreen agents widely used internationally can be roughly divided into different types according to their different mechanisms. There are two types, namely UV absorbers and UV scatterers. UV scattering desks mainly use certain inorganic substances to scatter or reflect UV light to reduce UV damage to the skin, such as kaolin, zinc oxide, talc, titanium oxide and new organic powders. They mainly form a barrier layer on the skin surface to prevent ultraviolet rays from directly irradiating the skin. However, this substance has the disadvantages of large dosage and poor sun protection effect. Excessive use can easily clog pores and cause new skin diseases and other adverse consequences. The current sunscreen refers to an ultraviolet absorber that absorbs ultraviolet rays.

The light energy their molecules absorb from ultraviolet rays is equal to the energy required to cause "photochemical excitation" of the molecules. This can convert the light energy into heat energy or harmless visible light and emit it, thereby effectively preventing ultraviolet rays from damaging the skin. Darkening and sunburn effects. Sunscreens can be divided into the following types:

2.1.1 Para-aminobenzoic acid (PABA) derivatives

P-aminobenzoic acid derivatives can effectively absorb 280-300 nm Ultraviolet rays are the earliest type of ultraviolet absorbers used. As UVB absorbers, they are irritating to the skin. Later, after improvement, its homologues--p-dimethylaminobenzoic acid appeared. They are mainly used as ultraviolet absorbers in sunscreen cosmetics to prevent ultraviolet erythema and dermatitis. Important foreign products include: para-aminobenzoic acid, glyceryl para-aminobenzoate, ethoxyethyl para-aminobenzoate and amyl para-aminobenzoate, etc. Commonly used UV absorber products in China include: 4-aminobenzoic acid, para-aminobenzoic acid monoglyceride, menthyl para-aminobenzoate, isobutyl para-aminobenzoate, and dimethyl octyl para-aminobenzoate. , p-Dimethylaminobenzoic acid, 2. Ethyl ethyl ester, etc. Among them, amyl p-dimethylaminobenzoate, glycerol p-aminobenzoate, etc. are all good UVB absorbers.

However, according to the American Skin Cancer Foundation, an analysis of cosmetics made from this type of ultraviolet absorber found that they may contain carcinogens, which may be the decomposition of ultraviolet absorbers. product. Therefore, it is now available in limited quantities.

2.1.2 Anthranilate derivatives

Anthranilate derivatives can protect against ultraviolet rays of 290-380nm and have the ability to protect against both UVA and UVB rays , is an effective UV absorber. It is cheap, but has low absorption rate and can be irritating to the skin. The main types of UV absorber products produced abroad include: menthyl anthranilate and high-menthol anthranilate. Moreover, octyl, N-dimethyl para-aminobenzoate, as a UVB absorber, can effectively prevent actinic carcinogenesis.

2.1.3 Cinnamate esters

Cinnamate esters can protect against ultraviolet rays of 280-310 nm and have high absorption rates, so they are widely used. ParsoMCX (octyl methoxycinnamate) is currently the most versatile sunscreen agent in the world. It has an excellent UV absorption curve, good safety, and good solubility in oily raw materials. Almost an ideal sunscreen.

The most widely used sunscreen or UV absorber in sunscreen cosmetics is undoubtedly isooctyl methoxycinnamate (ocMMethoxveinnamate), hereinafter referred to as OMC, the serial number of the EU Colipa sunscreen $28, below it is called Colipa$28, but its light resistance or photostability is not very high. Usually, after 10MED of sunlight radiation, about 70% of the active ingredients are photodegraded. So usually a higher dose needs to be added to the formula to make it work effectively. At the same time, in order to reduce the excessive irritation reaction of users with sensitive skin under the stimulation of sunlight after applying sunscreen cosmetics. It is necessary to add excess irritation-reducing ingredients to minimize product-related irritation complaints.

In the past few years. Some Nordic media once reported that certain UV absorbers used in cosmetics, such as OMC, benzophenone, 3 and 4, methylbenzylidene camphor, etc., may have aphrodisiac activity (Estrogenic Activity) and are not suitable for use in children's cosmetic crystals. , and caused a certain degree of panic among consumers in Europe. The European Scientific Committee on Cosmetics and Non-Food, which is responsible for the safety of cosmetics in the EU, has concluded after careful research that the above three suspected problematic UV absorbers have only weak aphrodisiac effects and are not compatible with many other commonly used cosmetic raw materials and certain drugs. The effect strength is about the same, and its use in cosmetics will not affect the health of consumers.

2.1.4 Salicylates

Salicylates are the earliest type of UV absorbers, which can form oxygen bonds within the molecule. Its own ability to absorb ultraviolet rays is very low, and the wavelength range it absorbs is extremely narrow (less than 340 Iiin), and it can prevent ultraviolet rays from 280-330nm.

However, after absorbing a certain amount of energy, due to molecular rearrangement, a benzophenone structure with strong UV protection ability is formed, resulting in strong photostability. As shown below.

Compounds with the above structural formula are also called pioneer UV absorbers. Their sun protection effect is not very high, but their prices are low, their preparation process is simple, and their toxicity is low. Can be used with other sunscreens.

The EU currently only allows the use of 3.3.5, trimethylcyclohexanol salicylate and isoctyl salicylate (c15H22O3). The previously allowed use of isopropyl benzyl salicylate is Use has been discontinued due to toxicological and other issues. The US FDA has relaxed restrictions on salicylic acid compounds: allowing the use of 3, 3, 5, trimethylcyclohexanol salicylate, isooctyl salicylate and triethanolamine salicylate.

Generally speaking, the absorption efficiency of salicylic acid compounds for short-wave UVB is quite low, which will inevitably lead to formulators increasing the dosage in order to achieve a certain SPF value. The photostability of this type of compound itself is very low. Its photodegradation products can cause major problems to the skin.

2.1.5 Benzophenone Compounds

Benzophenone-based sunscreens have strong absorption effects on almost the entire ultraviolet range because of the presence of molecules in their structure. Internal hydrogen bonding is an integrated ring formed by the intramolecular hydrogen bonding between the hydroxyl hydrogen on the benzene ring and the adjacent carbonyl oxygen. When ultraviolet light energy is absorbed, the molecules undergo thermal vibration, the hydrogen bonds are destroyed, and the integration ring is opened, thus converting harmful ultraviolet light into harmless heat energy and releasing it. In addition, after benzophenones absorb ultraviolet light, not only the hydrogen bond is destroyed, but the carbonyl group is excited, tautomerism occurs, and the enol structure is generated, which also consumes part of the energy. For example:

The strength of intramolecular hydrogen bonds is related to its photostability effect. The stronger the hydrogen bond, the greater the energy required to destroy it, and the more ultraviolet light energy is consumed by absorption, and the effect is The better; vice versa. This type of sunscreen is highly heat and light stable. However, it is unstable to oxidation, so when formulating colored cosmetics, antioxidants must be added to the formula. This type of sunscreen has good affinity to the skin and mucous membranes, will not cause photosensitivity reactions, and has low toxicity. For example, 2,hydroxy-4-methoxybenzophenone is an effective broad-spectrum UV absorber. It is more commonly used abroad. 2.2’ Monodihydroxy, 4.4’, Dimethoxybenzophenone have roughly the same sun protection effect in the ultraviolet A zone and ultraviolet B zone. It has high thermal and light stability. Tetrahydroxybenzophenone is a broad-spectrum UV absorber characterized by its highest potency in the tanning zone and its greatest thermal and light stability in its class. This type of sunscreen has ortho and para positions. The ortho position shows the absorption peak of UVA. Parallel position shows the absorption peak of UVB, so the range of UV absorption is wider than other sunscreens, and they are safe, and only a few people will have temporary allergic reactions. Therefore this is a widely used UV absorber.

2.1.6 Camphor derivatives

3-Phenyldecyl camphor can effectively absorb ultraviolet rays in the sunburn range, but can completely pass through the ultraviolet rays in the tanning range. For example, 3-(4-methylbenzyl) camphor can be used in various tanning agents and sunscreen agents. This type of sunscreen agent is stable during storage, has no irritation to the skin, no photosensitivity and variability, and has low toxicity, but is not easy to absorbed through the skin. Among them, benzylidene camphor was determined to be a better framework structure for photostable UV absorbers. The biggest advantage of this structure is that it undergoes a photoisomerization process under ultraviolet irradiation. That is, it can absorb ultraviolet energy. The ultraviolet rays are released as imperceptible heat by simply rotating the double bond connecting the benzene ring and the norbornane ring. This patronic anti-isomerization swing can be reversed, which ensures both photostability and safety of use.

2.1.7 Methane derivatives

It is a type of highly efficient UVA ultraviolet absorber that can be made into a sunscreen with SPF value. In foreign countries, such products are mainly 4-isopropylbenzoylmethane and 4-tert-butyl 4-methylaminobenzoylmethane. Another example is the product developed by the German company Givandan in recent years with the trade name Parsol 1789.

The name of DTFA is: Butyl methoxydlbenzeyl methane, which is called 4-butyl-4-methoxybenzoylmethane. The molecular formula is C20H22O3. It is a slightly yellow crystal grain with a slight aroma. Its main function is to prevent sun tanning. Kmax is 357 nm, the ultraviolet absorption band is 332. 385 nm, the sun protection factor SPF value has an increasing relationship with its dosage, and the SPF value can reach 9-10. Previously, the most effective of only a handful of UVA absorbers available was Pars01 1789.

Some plants contain chemical components that can absorb ultraviolet rays, and their extracts also have sunscreen properties, such as aloe vera, burdock, coix seed and Houttuynia cordata, as well as walnuts and rice bran oil, which also have high sunscreen properties. Sunscreen effect and good safety for skin. Will not cause adverse skin reactions. In addition, vitamin A can prevent connective tissue atrophy, speed up the repair of damage caused by ultraviolet light, improve skin composition, prevent connective tissue breakage and promote the synthesis of glycosaminoglycans. Vitamin E is an ideal antioxidant and anti-aging agent, which can inhibit the oxidation of unsaturated lipids and resist the damage of ultraviolet rays to the skin.

2.1.8 Inorganic sunscreen preparations

According to Cbandler M, manager of research and development of quality personal care products at Unlqema, “The latest research results that maintain the company’s product promise include transparency of inorganic TIO2. Suspensions that can be used in moisturizers, repair solutions and beach tanning products.” He specifically mentioned Solaveil CT-100 as the latest TiO2 dispersion with excellent transparency in the formulation.

Unlqema's innovations also include Arise vorsaex emulsion stabilizer technology for sunscreen sprays, inverse emulsification technology that maximizes the activity of Ar]acel P135 and is water-resistant, and Arlace 2121 liquid crystal stabilization The agent can achieve a particularly attractive and differentiated skin feel.

Thomson highlighted that "a recently completed study showed that Taiwan's microfine ZnO sunscreen formula has long-lasting UVA and UVB protection. This is because fine ZnO is completely photostable in the sun. This This fact can provide an important long-lasting protection function for products. ”

Thomson also said that in addition to inorganic fine ZnO, BASF has developed a new organic UVA filter that is effective in sunlight. It is also completely photostable and was launched at the International Cosmetics Fair under the trade name Uvinul A Plus. This new patented technology has many advantages over traditional organic filters Avobe nzono; Uvinul A Plus is completely photostable, does not require stabilization and is compatible with OMC and ZnO. Through practical patents, it can be combined with other common UV filters and has broad application prospects.

2.2 Sunscreen products

The use of different types of sunscreen agents in formulas (or the use of composite sunscreen agents) has become an important part of the development of today's sunscreen cosmetic crystal formula technology. This includes the combined use of UVB and UVA sunscreens, the combined use of UVB and UVA sunscreens, and the combined use of absorbers and scattering agents to better leverage the synergistic effect between sunscreen monomers. At the same time, it has become a new trend to use ultraviolet absorbers, ultra-fine scattering agents and some natural sunscreen ingredients such as aloe vera and marine life extracts in formulas. In order to reduce the skin problems that may be caused by some chemical absorbers, some formulators Add some anti-inflammatory agents to the product, such as A, bisabolol, DP300, etc.

In addition, different types of sunscreens should be used for different dosage forms of cosmetics. When preparing sunscreen lotions and gels, water-soluble and alcohol-soluble UV absorbers must be used; when preparing sunscreen oils, oil-soluble UV absorbers must be used. For certain beauty cosmetics. UV scattering agents can be used; cream cosmetics are best to use compound UV absorbers that are both oil-soluble and water-soluble to ensure that the active ingredients can be evenly distributed on the skin.

The higher the sun protection factor (SPP value is the ratio of the energy required to produce minimal erythema on skin protected by sunscreen products to the energy required to produce the same degree of erythema on unprotected skin), the higher the sun protection factor. The better the shielding effect of solar ultraviolet rays; however, the higher the concentration of organic ultraviolet absorbers added, the greater the possibility of causing skin allergies, and the more negative effects it will bring. Dermatologists believe that under normal circumstances, using sunscreen products with an SPF value of 15 is enough. The maximum should not exceed 30.

Tu Guorong and others from the Northwest Institute of Nuclear Technology screened and extracted dozens of plants with ultraviolet absorption, such as comfrey, sophora japonica and cinnamon. A variety of extracted natural flavonoids have good absorption of ultraviolet light. At the same time, they also have anti-inflammatory and anti-allergic functions by inhibiting lipid oxidation.

Recently, Ciba Refinement Co., Ltd. of Switzerland has launched a new type of UVA ultraviolet absorber, Telaisic M. TLC M has dual physical sunscreen effects, and its high photostability gives it high safety in practical applications.

In addition, when choosing a sunscreen, you should also select and prepare a suitable matrix. A good matrix will better exert the sunscreen effect of the sunscreen. For absorbable sunscreens, it is very important to choose a good anti-sunscreen carrier. A carrier that is easy to spread, has good affinity with the skin and has strong water resistance will undoubtedly be more suitable for the role of sunscreen. Some special structures The addition of high molecular polymers can improve the actual sun protection ability of the product. For scattering sunscreens, choosing the appropriate matrix is ??equally important. Studies have shown that the refractive index of inorganic powder has a great relationship with the scattering of light. The greater the ratio of the refractive index of the powder to the refractive index of the matrix, the greater the amount of ultraviolet light reflected from the surface of the powder. Therefore, people began to pay attention to using inorganic sunscreen agents such as titanium dioxide and zinc oxide while trying to use matrix materials with low refractive index in the formula.

3 Outlook

As people’s understanding of the hazards and benefits of ultraviolet rays continues to deepen; from the perspective of the development of new sunscreen technologies and new raw materials, a number of promising studies are underway Developed worldwide, they are: research on the efficiency of ultrafine inorganic particles scattering and absorbing ultraviolet rays and their applications; research on amino acid UVA absorbers and marine organisms rich in amino acids and high concentrations of tyrosine for sunscreen cosmetics; Melanin (including natural, biological and synthetic) with good sunscreen properties is used in the research of sunscreen products. The application of UV absorbers in sunscreen cosmetics will definitely be further expanded. New UV absorbers that are photostable, have low dermal permeability and have high absorption in the whole wavelength range will definitely bring about innovation and progress in formulation technology. We used a UV energy meter to measure the change in the energy of ultraviolet rays when they reach the ground in an intolerable environment. We found that even on cloudy or cloudy days, ultraviolet rays with strong energy reach the ground. The energy of ultraviolet rays reaching the ground in spring is no more than that in summer. Much lower; UV can penetrate more clothes, glass and water to reach human skin. Sun protection is not only needed in hot summers and not only for the skin. Sun protection will be a long-term topic surrounding the development of modern cosmetics technology and market.