The Science Behind Surfactants

Surfactants are among the most versatile raw materials in cosmetic formulations. But with that versatility comes complexity. Not all surfactants clean the same way. Some emulsify, some solubilize, some foam and some do none of the above.

Let’s break down what surfactants really are, what they do in your products, and how to choose the right one based on performance and compatibility.

What Is a Surfactant?

A surfactant (short for “surface-active agent”) is a molecule with two distinct parts:

• A hydrophilic (water-attracting) head

• A lipophilic (oil-attracting) tail

This dual nature allows surfactants to interact with both water and oil, making them essential for:

• Lifting dirt and oils from skin and hair

• Creating emulsions

• Solubilizing oils or actives into water

• Generating foam or lather (in some cases)

Main Roles of Surfactants in Formulas

1. Cleansing

This is the most familiar role, especially in shampoos, body washes and facial cleansers. Surfactants surround oil and dirt, forming micelles that trap it, suspend it in water, and allow it to be rinsed away.

2. Emulsifying

Some surfactants (or surfactant blends) can stabilize emulsions, particularly in oil-in-water systems. These are often used alongside co-emulsifiers and thickeners for long-term stability.

3. Solubilizing

When you need to incorporate a small amount of oil, essential oil, or fragrance into a water-based product, you’ll often reach for a solubilizing surfactant—one that forms clear or translucent microemulsions.

4. Foaming

Not all surfactants foam, but some (especially anionic types) create rich lather. While foam doesn’t equal cleansing, it affects user perception—especially in rinse-off products.

Types of Surfactants (Based on Charge)

Understanding surfactant charge is critical for performance and compatibility.

Most modern cleansers use blends of these to balance cleansing power, foaming, mildness, and feel.

Choosing the Right Surfactant for Your Formula

Start by asking a few key questions:

1. What is the product format?

• Rinse-off (e.g., cleanser, shampoo): Prioritize cleansing power and foam aesthetics

• Leave-on (e.g., micellar water): Use ultra-mild, low-foaming systems

2. What’s your pH target?

Surfactant charge and solubility shift with pH. Some amphoterics and anionics become unstable or irritating outside certain pH windows.

3. Who is it for?

Children’s, sensitive skin, or barrier-repair products should use mild surfactant systems like nonionics and amphoterics, often paired with moisturizers or conditioning agents.

4. Do you need solubilization or emulsification?

Use surfactants designed for that function like PEG-40 hydrogenated castor oil for fragrance solubilization or polysorbate 80 for oil solubilization.

Common Surfactants by Use

For Cleansing:

• Sodium cocoyl isethionate (SCI) – Mild, good foam

• Cocamidopropyl betaine – Amphoteric, foam booster, mild

• Disodium laureth sulfosuccinate – Ultra-mild anionic

For Solubilizing:

• PEG-40 hydrogenated castor oil

• Polysorbate 20 or 80

• Caprylyl/capryl glucoside

For Emulsifying (Surfactant-based systems):

• Ceteareth-20

• Sodium stearoyl lactylate

• Sorbitan stearate with polysorbate 60 (HLB pair)

Final Note: Mild Doesn’t Mean Ineffective

There’s a tendency to equate “gentle” with “weak.” But well-formulated surfactant systems can cleanse effectively without stripping the skin barrier.

Choose surfactants that do their job without overdoing it, especially when combined with skin-conditioning agents or barrier-repair ingredients.