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How to Select Natural Surfactants

A surfactant is a surface active agent, known for having the ability to clean dirt and to create foam.

Surfactants are described for the role they play in a formulation, for instance, foam is the finished product, the surfactants used may be referred to as “foaming agents.” Surfactants used in body and hair care may be termed “detergents” or “soaps.” Foaming is not necessarily related to cleansing, a product does or does not foam a lot, has no direct connection on how well the product function as a cleansing agent. However, often the consumers believe in how well a product cleans, is to see a relatively high level of foam to think that the product is cleaning or working effectively. Contrary to this popular belief, you do not need a lot of foam to clean a surface properly. Foam is just air trapped by the surfactant. Technically, we only need enough surfactant to lift all the oil and dirt from the surface. 

How a Surfactant Works

Surfactants consist of two separate components – the hydrophilic or water-loving head, and the hydrophobic or water-hating tail.

This is a simplistic diagram to give you an overview of how a surfactant looks like. Some surfactants may have multiple or more complex head or tail groups. 

Dirt attached to the skin is often oil-soluble, so when soap or cleansing product is applied to the skin, the surfactant lowers the surface tension of the water. The hydrophobic tail of the surfactant is then attached themselves to the dirt and the oil, assemble in a geometric pattern which is called micelle. As dirt and grease are completed surrounded by the hydrophobic tails, the micelles with the oil, dirt, and surfactant are removed with water during the rinse. 

There are 4 types of surfactants based on their interfaces and charges: nonionic, anionic, cationic, amphoteric.

A nonionic surfactant has no charge groups in its head. If the charge is negative, the surfactant is more specifically called anionic. If the charge is positive, it is called cationic. Amphoteric surfactants which have either a positive or negative charge depending on the pH environment.

Picture Source: ipcol.com 

Generally, formulators will need to have idea of each group of natural surfactants and how they will play a role in the cleansing products.

1. Anionic Surfactants:

Anionic surfactants are the most commonly used surfactants because they deliver high foaming, high cleansing, and high washing capabilities in a finished product. Anionic surfactants have a negatively charged water-loving head, applied as primary or secondary surfactants in cleansing products (rinse-off). However, it can be harsh on the skin, so it is good to combine with other types of milder surfactants or add amphoteric surfactants to balance out the anionic surfactants. 

Most commonly used anionic surfactants, SLS (Sodium lauryl sulfate or Sodium Laureth Sulfate). It can be found in everything from shampoos and shower gels. 

Common Uses: 

All cleansing & foaming products: shampoo, shower gel, micellar water, bath foam, shaving cream, etc

Examples of Natural Anionic Surfactants:

  • Disodium Coco-Glucoside Citrate
  • Sodium Coco-Glucoside Tartrate
  • Sodium Cocoyl Glutamate
  • Di-sodium Cocoyl Glutamate
  • Sodium Lauroyl Sarcosinate
  • Sodium Myristoyl Sarcosinate
  • Oat amino acid surfactants
  • Apple amino acid surfactants
  • Silk amino acid surfactants
  • Barley amino acid surfactants
  • Wheat amino acid surfactants

2. Amphoteric Surfactants

Amphoteric surfactants can carry either a positive or negative charge depending on the pH of the product. It is widely used because of their adaptability. If you want to formulate a product with nourishing and conditioning properties, choose an amphoteric surfactant to give the final product a lower pH. However, with a higher pH, the amphoteric surfactant will work more like an anionic surfactant, will deliver high foaming and cleansing capabilities. When used alone, amphoteric surfactants will give you a gentle cleansing product. When an amphoteric surfactant is coupled with an anionic surfactant, the amphoteric surfactant reduces the harshness of the anionic surfactants and help to stabilize their foam. They tend to be very mild surfactants, can be used alone or combined with any other of the surfactant groups.

Common Uses: 

All cleansing and foaming products, conditioning and anti-frizz & detanglers

Examples of Natural Amphoteric Surfactants:

  • Cocamidopropyl betaine
  • Sodium Cocoamphoacetate
  • Sodium Lauramphoacetate

3. Cationic Surfactants

Cationic surfactants are the opposite of anionic surfactants. They have a positively charged water-loving head. When used alone, do not have high foaming capabilities. These surfactants are often used where foaming is not necessary, such as in hair conditioners. Their positive charge is attracted to the negative charge in hair, this reduces the amount of electrostatic charge in hair, making your hair more manageable and helps prevent damage. Cationic surfactants work well with both amphoteric (either a positive or negative charge) and nonionic surfactants (no charge). Cationic surfactants are not usually compatible with anionic surfactants because of the opposing charge will not combine.

Common Uses: 

Hair conditioner, co-wash, cleansing conditioner, conditioning shampoo, conditioning balm, anti-frizz, and detanglers

Example of Natural Cationic Surfactant:

Only non-quaternary cationic surfactant which is accepted in natural formulations.

4. Nonionic Surfactants

Nonionic surfactants do not have an ionic charge in their water-loving heads. These surfactants are excellent as an emollient, softening, and soothing skin can stabilize foam in the formulation. These surfactants have no foaming capabilities and are rarely used as the main surfactant, usually used as complementary or secondary surfactants. Because they don’t carry a charge, they are the most compatible with other types of surfactants. Nonionic surfactants are gentler when cleaning, can also be used in formulations to reduce irritants, due to their gentle cleansing ability.

The second most commonly used surfactants are nonionic surfactants. They don’t ionize in water or aqueous solutions. Because they don’t carry a charge, they are the most compatible with other types of surfactants. Recently, sugar-based nonionic surfactants have been developed to offer a safer, non-toxic alternative to some of the more harsh surfactants on the market up until now.

Common Uses: 

Almost all products from shampoo to conditioner and everything in between

Examples of Natural Nonionic Surfactants:

  • Soapwort
  • Soap nut
  • Yucca Schidigera extract
  • Quillaja saponaria extract
  • Coco glucoside
  • Decyl glucoside
  • Lauryl glucoside

 

Often, it is hardly seen finished products use only one single surfactant. 2 or more surfactants are usually blended to:

A. Reduce the sensitization and enhance mildness

B. Improve foam volume, texture, and stability

C. Enhance the viscosity and texture of the product

Summary Table

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