Stearic Acid in Cleansers: What It Does (CAS 57-11-4)
You may have had this experience: picking up a facial cleanser, turning to the ingredient list, seeing the words “Stearic Acid“, and your heart skips a beat — “Acid? Is it the same as acid peeling? Will it feel tight and stinging after use?”
This concern is not strange. In recent years, the term “acid peeling” has appeared too frequently, and many people automatically associate “acid” with exfoliation, peeling, and irritation. However, in the ingredient list, stearic acid is usually not the kind of “acid” used for exfoliation (such as fruit acid, salicylic acid, etc.). It is more like a “structural component” in the formula: making the paste more shaped, the foam finer, the skin feel smoother, and even making the product more stable at different temperatures.
Even more unexpected is that it is supporting the wear resistance of rubber tires, the firmness of plastic pipes, and the stable burning of candles on a huge industrial scale.
From gentle care in the bathroom to hardcore manufacturing in the factory, how exactly does Stearic Acid (CAS 57-11-4) cross such a huge application gap? As a purchaser or formulation engineer, how should you choose the most suitable one among the complex market specifications?
Table of Contents
- Chapter 1: What exactly is Stearic Acid?
- Chapter 2: Application Scenarios of Stearic Acid
- Chapter 3: Why is Stearic Acid so "Universal"?
- Chapter 4: Core Model Analysis
- Chapter 5: Deep Purchasing Decision Guide
- Chapter 6: Frequently Asked Questions (FAQ)
- Conclusion: Choosing the Right One is the Best
- Our Laboratory and References
- References and Data Sources
Chapter 1: What exactly is Stearic Acid?
1.1 What is it
In the international trade of chemical raw materials, the general ID number of stearic acid is CAS 57-11-4 (Note: In the industry, this type of C16/C18 mixed fatty acid is often sold under the trade name stearic acid. CAS labeling may differ under different regulations/registration calibers, and SDS and regulatory registration shall prevail).
From a chemical definition, it is a long-chain saturated fatty acid with the chemical formula C18H36O2, and the scientific name is “Octadecanoic Acid“.
What does “long chain” mean? Its molecular structure is like a long tail, and this tail has strong hydrophobicity (lipophilicity). This allows it to have good compatibility in oils and fats, usually dissolving more obviously under heating conditions, and participating in system structure formation during the cooling process.
What does “saturated” mean? This means that there are no unstable double bonds in its molecular structure. Compared with unsaturated fatty acids that are easy to oxidize (for example, some vegetable oils will have a rancid smell after being left for a long time), stearic acid is very stable, not easy to oxidize, and not easy to deteriorate, which is also the reason why it has become the preferred matrix for many products.
1.2 Is it a pure substance?
This is a detail that is often overlooked in purchasing but is crucial.
In the laboratory, you might be able to buy stearic acid reagents with a purity of 99.9%. But in industrial production, the “stearic acid” we talk about is usually a mixture. It is mainly composed of two saturated fatty acids: C18 (Stearic Acid) and C16 (Palmitic Acid).
Why is this so? Because industrial stearic acid mainly comes from natural oils (such as palm oil or tallow). In nature, C18 and C16 are often born together. According to different separation processes, the ratio of C18 to C16 will change, and this ratio directly determines the physical properties of stearic acid, such as melting point and hardness.
This point is very critical, and we will interpret it in detail in the purchasing guide later.
1.3 Physical perception
If you get a standard sample from Shandong Zhishang New Material, you will see it presenting a white or slightly yellow appearance. Depending on the processing form, it may be pearl-like particles (Beads), or flake-like (Flakes) or powder (Powder).
Touching it with your hand, it has a unique waxy greasy feeling; smelling it closely, high-quality stearic acid has almost no odor, or carries an extremely faint, pleasant fatty scent.
Chapter 2: Application Scenarios of Stearic Acid
2.1 Daily Chemical and Personal Care
2.2 Food and Pharmaceutical Industry
2.3 Rubber and Plastic Industry
2.1 Daily Chemical and Personal Care
Back to the question at the beginning of the article, what exactly is stearic acid doing in skin care products?
The “Skeleton” of cleansing products: In soap-based facial cleansers, stearic acid reacts with alkaline agents to generate stearates (i.e., soap). It is one of the important contributors to the richness and fineness of foam, and also provides that unique “sense of cleanliness” after washing.
The “Stabilizer” of emulsions: In moisturizing creams, it acts as an auxiliary emulsifier to help water and oil “coexist peacefully” and prevent product stratification. At the same time, it can also adjust the viscosity of the product, so that the cream does not flow or feel heavy when applied to the face, presenting a high-grade pearlescent luster.
The “Shaping Agent” of makeup: In lipsticks and foundation sticks, the higher melting point of stearic acid helps the paste maintain its shape, and it will not easily melt or break even under the lukewarm temperature of pockets in summer.
2.2 Food and Pharmaceutical Industry
In these fields, relevant ingredients/additives are sometimes labeled as E570 (Fatty Acids).
Tableting candy and pills: Imagine, why can pills take shape under high-pressure stamping by machines and have a smooth surface? Because stearic acid and its salts (such as magnesium stearate) act as lubricants in them. It prevents powder from sticking to the mold, ensuring that every pill is intact.
Chewing gum and gum base: It acts as a softener, keeping chewing gum with a soft chewing texture, and will not become hard due to long-time storage.
2.3 Rubber and Plastic Industry
If the daily chemical field utilizes its “physical texture”, then the industrial field utilizes its “chemical activity” and “lubricating performance“.
Rubber tires (Activator): This is one of the fields with huge consumption of stearic acid. In the rubber vulcanization process, stearic acid is usually used in conjunction with zinc oxide. It can help zinc oxide dissolve in the rubber system, thereby effectively activating the vulcanization system. Simply put, lacking stearic acid, the vulcanization efficiency and processing performance of tires will be greatly discounted.
PVC Plastic (Processing Aid and Lubricant): Stearic acid and its metal salts (such as calcium/zinc stearate) are often used in PVC processing. Free stearic acid mainly plays the role of “lubricant” in it, reducing the friction between the plastic melt and the metal surface of the machine, preventing the plastic from scorching and decomposing due to local overheating in the machine. At the same time, it can also endow the pipe surface with a smooth and bright appearance.
Chapter 3: Why is Stearic Acid so "Universal"? Three Capabilities Brought by One Molecular Chain
Stearic acid can cross daily chemicals and industry because its structure is very “typical”:
One end is a carboxylic acid group (easier to participate in reactions, form salts with alkali or metal ions);
The other end is a very long hydrocarbon chain (more oily, affecting friction and compatibility).
This type of structure brings three very common capabilities that are easy to implement in practice:
1. Making the system more stable and shaped
2. Making cleaning and foam more controllable
3. Making processing smoother and friction smaller
1. Making the system more stable and shaped
In cream or soap base systems, formulators often need to control two things:
Can the shape you squeeze out “stand up“;
After putting it for a period of time or experiencing temperature changes, is it easy to separate oil, stratify or become thin.
Stearic acid is often related to these goals because it can participate in forming a more “solid” system structure. The “thick, smooth, delicate” feeling you feel on your hands is often the formulation structure at work behind the scenes.
2. Making cleaning and foam more controllable
In soap or certain cleaning systems, the reaction of fatty acids with alkali to generate fatty acid salts is a classic path. Stearates are related to “foam, hardness, molding” in many formulas.
The same logic also explains: why “composition differences of raw materials” affect the final body feeling — because the system structure has a perception of the “fatty acid chain length combination”.
3. Making processing smoother and friction smaller
Long hydrocarbon chains often mean stronger hydrophobicity and certain lubricating characteristics. In scenarios such as plastic processing and rubber mixing, these characteristics are often used to improve processing flow, reduce sticky roll tendency or improve demolding performance (specific effects still depend on the system and formula).
Chapter 4: Core Model Analysis — What do 1801, 1840, 1860 represent?
For purchasing managers, the biggest confusion often comes from the choice of models. The market is full of number codes like “1801”, “1840”, and terms like “Triple Pressed“, “Double Pressed“. What exactly do they represent?
These terms originate from early production processes — separating solid fatty acids and liquid fatty acids through multiple pressings. Although modern factories mostly use advanced distillation and hydrogenation technologies, these traditional names are still retained as industry standards, representing different purity grades. (Note: Naming of various models and indicator boundaries may differ between different manufacturers, and the technical agreement/COA and testing methods confirmed by both parties shall prevail.)
4.1 Stearic Acid 1801 (Triple Pressed)
4.2 Stearic Acid 1840 / 1842 (Double Pressed)
4.3 Stearic Acid 1860 (Single Pressed)
4.1 Stearic Acid 1801 (Triple Pressed)
This is the highest grade of stearic acid.
Features: It has undergone the strictest purification process. Its iodine value is extremely low (usually < 1.0 g/100g), meaning very few unsaturated components and extremely strong oxidation resistance. The color is the whitest and the odor is the smallest.
Typical Composition: About 45% C18 and 55% C16 (the ratio may vary slightly by manufacturer, but the purity is extremely high).
Applicable Scenarios: High-end cosmetics, pharmaceutical excipients, food additives, high-grade light-colored plastic products. For fields with strict requirements on color, odor, and long-term stability, 1801 is a common preferred choice.
4.2 Stearic Acid 1840 / 1842 (Double Pressed)
This is a general-purpose product with balanced performance.
Features: Purity is slightly lower than 1801, iodine value is controlled in a lower range (usually < 4.0), and color is good.
Applicable Scenarios: Ordinary daily chemical products, candles, industrial lubricants, textile auxiliaries. For customers who pursue cost-effectiveness and do not have absolute requirements for extreme whiteness, 1840 is an ideal alternative.
4.3 Stearic Acid 1860 (Single Pressed)
Usually called “Rubber Grade Stearic Acid“.
Features: Allows a slightly higher proportion of unsaturated fatty acids (iodine value is relatively high, possibly between 8.0-15.0), and impurity content is relatively tolerant.
Applicable Scenarios: Rubber tires, dark rubber products, release agents, metal polishing pastes. In these applications, chemical activity is more important than color, and rubber itself is mostly black, so it is not sensitive to the yellowing of raw materials.
Chapter 5: Deep Purchasing Decision Guide — How to Choose, Compare, and Inspect
As Shandong Zhishang New Material Co., Ltd., we deeply know the pain points of purchasing personnel. Facing uneven quotations and dazzling parameter sheets (COA), how to ensure that the raw materials you buy will not cause production accidents?
This chapter will provide you with a combat-level purchasing checklist.
Do not just ask the supplier “how much per ton”, first clarify your application scenario, because different industries define “qualified” completely differently.
Industrial Grade Customers: You focus on physical processing performance. Focus on asking about lubricity, dispersion, and impact on rheological properties. Acceptance standards are usually based on enterprise internal control indicators or industry general standards.
Daily Chemical Grade Customers: You focus on sensory experience. Is the color white enough? Does the smell affect the performance of the fragrance? Is it clear after heating and dissolving?
Food/Pharmaceutical Grade Customers: You focus on compliance and safety. Are there heavy metal residues? Are there solvent residues? Can the supplier provide testing reports that comply with Pharmacopoeia (USP/EP/CP) or food safety regulations?
When getting the supplier’s quality inspection sheet (COA), please focus on the following five core indicators. We not only tell you “what to look at”, but also tell you “why to look at it”.
(1) Iodine Value
What to look at: The lower the value, the better (for high-end products).
Why look at it: This is one of the important indicators for judging the stability of stearic acid. Iodine value represents the number of unsaturated double bonds in the molecule. Double bonds are like “gaps” on the molecule, easily attacked by oxygen.
Risk Warning: If you are making white candles or light-colored plastics and use stearic acid with a high iodine value, the product may inexplicably turn yellow or even produce a rancid smell after being stored on the shelf for a few months.
(2) Acid Value
What to look at: Whether it is within the standard range (e.g., 200-210 mgKOH/g).
Why look at it: This reflects the molecular weight and purity of the product (Note: Some suppliers will also provide saponification value indicators, which need to be understood in combination with the product form).
Risk Warning: In rubber or saponification reactions, the formula calculates the feeding amount based on the acid value. If the acid value fluctuates too much, it will lead to incomplete reaction (product sticky) or excessive reaction (product brittle).
(3) Melting Point / Titer
What to look at: Usually between 52°C – 60°C.
Why look at it: Determines the processing window of the factory (Note: The test methods for the two are different, subject to agreement).
Risk Warning: Too high a melting point may make it difficult to melt during mixing, forming “white spot” defects; too low a melting point may cause raw materials to cake during transportation in summer, or finished lipsticks to soften at high temperatures.
(4) Composition Distribution (C18 / C16 Ratio)
What to look at: Gas Chromatography Analysis (GC) results.
Why look at it: This is a detail that is often concealed. Also being 1801 stearic acid, some manufacturers have a C18 content of 40%, and some are 50%.
Risk Warning: The C18/C16 ratio will significantly affect the freezing point, crystal morphology, and structural strength. If the supplier changes the ratio without notification, even if other indicators are qualified, your final product texture may change drastically (for example, the cream suddenly becomes thin). It is recommended to require the supplier to lock this ratio range.
(5) Color
What to look at: Hazen color number or Lovibond color comparison.
Why look at it: Directly affects the appearance of the final product. For transparent or pure white products, color is a “one-vote veto” indicator.
In addition to parameters, the background of raw materials is also the focus of modern supply chains.
Plant Source vs Animal Source:
Currently, the international mainstream trend favors plant sources (palm oil based).
Advantages: Plant-source stearic acid usually smells fresher and is easier to obtain Halal and Kosher certifications, helping your end products export to Southeast Asian or Middle Eastern markets. Animal-source products still have applications in certain specific markets (such as certain specific types of candles), but global compliance is not only limited but also involves epidemic prevention barriers such as mad cow disease.
Particle Type Selection:
Beads/Microbeads: Good fluidity, no dust, suitable for automated feeding systems, currently the most popular form.
Powder: Fast mixing and dispersion speed, but large dust, workshop environment is difficult to control, and there is a risk of dust explosion, requiring cautious operation.
Flakes: Traditional form, medium dissolution speed.
Professional suppliers sell not only raw materials but also a full set of compliance guarantees. Before placing an order, please confirm whether the supplier can provide the following “Delivery List”:
COA (Certificate of Analysis): Must be provided with every batch of goods, and data must be true.
SDS (Safety Data Sheet): Detailed data sheet covering safe operation, storage, and emergency handling, which is a document that the factory safety supervision department must check.
Compliance Statement:
REACH SVHC: If your product is exported to the EU, this is mandatory.
RoHS: The electrical and electronic industry must confirm that it does not contain specific hazardous substances.
RSPO (Sustainable Palm Oil): For multinational corporate customers, proving that raw materials have not destroyed rainforests is the ticket to enter the supply chain.
Traceability Statement: Can the raw material origin and production batch be traced? This is an important part of the quality management system (ISO 9001).
Chapter 6: Frequently Asked Questions (FAQ)
A: Most specifications are usually not managed as hazardous goods under common regulatory systems, but should still be subject to the transportation information in the SDS and carrier requirements. It is stable in nature, but attention should be paid to moisture prevention, sun protection, and staying away from fire sources during storage. Although it is not flammable, powder state reaching a certain concentration in the air may have a dust explosion risk when encountering an open flame, so the warehouse should maintain good ventilation and dust removal.
A: This is usually because the C16/C18 carbon chain distribution has fluctuated, or the crystal structure is different during the cooling process. General COAs often only list macroscopic indicators such as acid value and iodine value, and may not necessarily list detailed carbon chain ratios. If you have extremely high requirements for process stability, it is recommended to communicate with us to lock specific carbon chain distribution ratios.
A: Under dry and cool storage conditions, stearic acid is very stable, and the shelf life is usually two years. The so-called “expiration” mainly refers to slight oxidation that may cause color yellowing or slight changes in acid value. If used for rubber products that are not sensitive to color, it can often still be used after re-testing indicators are qualified; but if used for cosmetics or medicine, it is recommended to strictly abide by shelf life regulations.
A: It is recommended to choose 1840 or 1842 grade plant-source stearic acid. This grade achieves a good balance between cost and whiteness. At the same time, the plant-source identity can help you avoid regulatory restrictions on animal-source ingredients in European and American markets.
Conclusion: Choosing the Right One is the Best
From the perspective of molecular structure, stearic acid may just be simple C18H36O2, but in practical application, it is an important bridge connecting natural resources and modern industrial civilization.
Whether you are a formulation engineer developing a new gentle cleanser or a purchasing manager shouldering the heavy responsibility of maintaining stable production in a tire factory, choosing a stearic acid with stable quality and suitable specifications is crucial. Wrong selection may not only lead to cost waste but also cause risks of production line shutdown or end-product recall.
At Shandong Zhishang New Material Co., Ltd., we not only provide raw materials, we provide solutions based on scenarios. We deeply understand the subtle needs of different industries for indicators, and through source direct procurement and strict quality control systems, ensure that every bag of stearic acid delivered to your hands can become the solid cornerstone of your product quality.
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Our Factory
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References & Data Sources
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1. Product Identification & Basic Information
PubChem: Stearic Acid Compound Summary. National Library of Medicine (NIH). [Link] -
2. Physicochemical Properties
NIST Chemistry WebBook (Octadecanoic acid / Stearic acid, CAS 57-11-4). National Institute of Standards and Technology (NIST). [Link] -
3. Research & Application Studies
Effect of stearic acid on the properties of span 60-agar bigel network. ScienceDirect. [Link] -
4. Industrial & Chemical Context
American Chemical Society (ACS) Molecule of the Week：Sodium stearate. American Chemical Society (ACS). [Link]