5cst silicone oil in cosmetics （HC-YM6292） ------deciphering the aesthetics of science and technology of "invisible skin care film

Ⅰ. Characterization of 5cst Silicone Oil

5cst Silicone Oil, as a low viscosity Polydimethylsiloxane (PDMS) with a viscosity of 5 centistokes, has a wide range of applications in the cosmetic field due to its excellent properties. 5cst Silicone Oil, due to its unique physicochemical properties, is able to enhance the skinfeel of the product, improve the spreadability of the product, and give products specific functionality. It has the following core properties:

Light texture: molecular weight of about 500-650, texture as refreshing as water, completely non-greasy feeling;

Breathable film: It can form a breathable film of 0.1-0.3μm on the skin surface without affecting the evaporation of sweat;

Chemically inert: pH stable (3-9), high temperature resistant (-40℃~200℃), does not react with most components;

Excellent spreadability: surface tension is as low as 21mN/m, 1/3 of water, realizing the effect of "one wipe is even".

Technical indicators：

Safety and Regulatory Compliance

Toxicologic data:

Acute oral toxicity LD50 >5000 mg/kg (rat), non-sensitizing (negative HRIPT test);

The EU SCCS recognizes the maximum safe use of 5cst silicone oils in cosmetics at 15%.

Environmental Challenges:

Biodegradability is only 3% (OECD 301B test) and needs to be used with degradable silicone (e.g., phenyltrisiloxane).

Ⅱ. 5cst silicone oil plays a "role"：

First of all, 5cst Silicone oil is widely used in skin care products for its excellent lubricity and spreadability. Its low viscosity allows it to spread quickly and evenly over the skin's surface, forming a thin, light, breathable protective film that reduces water loss and moisturizes the skin. At the same time, this silicone oil film can fill in the fine texture of the skin surface, making the skin feel smoother and more delicate to the touch and improving the visual effect. Especially in creams and lotions, 5cst silicone oil can effectively reduce the greasiness of the product, bringing a refreshing and comfortable experience.

Secondly, 5cst Silicone oil also plays an important role in makeup products. In primers such as foundations and BB creams, it serves as a dispersant to help evenly disperse pigments, thereby improving product coverage and reducing the phenomenon of powder sticking. In addition, the waterproof nature of silicone oil enhances the hold of the product, making the makeup last longer. In lipsticks, lip glazes and other lip products, 5cst silicone oil can give the product a silky texture and enhance its coloring effect.

In addition to improving skin feel and enhancing makeup effects, 5cst silicone oil can also be used as a functional ingredient to give cosmetics specific benefits. For example, in sunscreen products, it can be used as a film-forming agent to help sunscreens adhere better to the surface of the skin, thus improving sun protection. In anti-aging products, silicone oil can be used as an antioxidant to help fight free radicals and slow down skin aging.

Ⅲ. The five major application scenarios of 5cst silicone oil in cosmetics

1. Primers: creating a "second skin"---Foundation/air cushion:

Function: Fill the gaps in the stratum corneum, smooth pores and fine lines, make the powder evenly distributed (particle size matching degree of more than 90%);

Formulation Case: Estee Lauder DW Foundation uses a 5cst silicone oil + silica complex system that extends makeup holding time to 16 hours.

Makeup primer:

Forms a network of directionally aligned silicone to enhance subsequent makeup adhesion and minimize creasing.

2. Sunscreen products: the invisible shield---Chemical sunscreen enhancement:

Solubilizes oil-soluble sunscreens such as Avobenzone and improves photostability (40% reduction in the attenuation rate of UVA protection);

Experimental data: sunscreen with 5% 5cst silicone oil added boosted SPF by 15% (J. Cosmet. Sci., 2021).

Physical sunscreen soft focus:

Coated titanium dioxide particles to reduce the "false white" phenomenon and optimize the particle size distribution from 1.2μm to 0.8μm.

3. Skin care serums: "express delivery" of potent ingredients---Promoting osmotic systems:

Complexed with cyclopentasiloxane (D5) (3:7) to form a "silicon channel" that increases retinol transdermal permeability by a factor of 3;

Case in point: the Thule CE Essence wraps 15% Vitamin C in 5cst silicone to prevent oxidative discoloration.

Slow-release technology:

Silicone oil was added to the microencapsulated walls to control the rate of nicotinamide release to 0.2 mg/cm²/h.

4. Hair care products: the invisible armor of hair---Shampoo:

Repair of scales: at pH 4.5, the silicone film binds to keratin through hydrogen bonding, reducing the coefficient of friction by 60%;

Hair care essential oils:

Thermal protection: Silicon film can control the hair core temperature within 180℃ when blowing at 230℃ (infrared thermal imaging data).

5. Innovative dosage form: overturning traditional texture---Water Sense Makeup Remover:

5cst silicone oil as a continuous phase with PEG-20 glyceryl triisostearate to achieve "second emulsification in water";

Solid Essence Stick:

Compound with beeswax (ratio 1:4), melting point control at 36 ℃, touch the skin immediately melt non-sticky.

IV. Key technical points in formulation design

1. Compatibility management---Pairing with actives:

Avoid pairing with highly polar ingredients (e.g., sodium hyaluronate), and silanization-treated ingredients are recommended;

The compatibility concentration with vitamin E acetate should be <8%, otherwise it is easy to precipitate crystals.

Emulsification system selection:

PEG/PPG type emulsifiers (e.g. PEG-10 polydimethylsiloxane) are recommended, with HLB values controlled at 4-6.

2. Stability optimization---Anti-layering techniques:

The viscosity was increased from 5 cst to 1200 cst (rest recovery) by adding 0.5% fumed silica (Aerosil R972) as a thixotropic agent; 

Anti-yellowing program:

With 0.01% BHT (butylated hydroxytoluene) + 0.1% tocopherol, the color difference value ΔE<1.5 in the accelerated test at 45℃.

3. Sensory experience design---Refreshing metrics:

The "stickiness index" of 5cst silicone oil was 2.1, which is much lower than that of mineral oil (8.7), as measured by a sensory evaluator;

Gloss level regulation:

By adjusting the silicone/mica ratio (1:3 recommended), a precise adjustment from matte to satin can be realized.

V. Future Trends: Three Major Breakthrough Directions in Silicone Oil Technology

Smart Response Silicone Oil:

pH-sensitive silicone oils (e.g., amino modifiers) that automatically enhance adsorption at sebum pH 5.5;

Green synthesis process:

Enzyme-catalyzed production of silicone oil with 70% lower energy consumption (BASF has achieved pilot testing);

Bionic structural design:

Branched chain silicone oils that mimic skin lipids (e.g., C30-45 alkyl dimethicones), with a 50% improvement in skin friendliness.

Conclusion:

As the "liquid optical lens" of the cosmetic industry, 5cst silicone oil is redefining the boundaries of skincare and beauty through the regulation of texture at the molecular level. From the "zero powder" revolution of foundation to the "invisible shield" of sunscreen, its application has transcended the role of a traditional lubricant to become the core engine of formulation innovation. With the breakthroughs in green chemistry and molecular bionics, this classic ingredient will continue to release its technological charm.

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