The Science of Cleansing

Why do we need to cleanse?

The initial step in any skincare routine, whether face or body, is cleansing. Cleansing is an important process because it removes dirt, excess sebum or oil, dead skin cells, microorganisms or any products you might have applied during the day.

How do cleansers work? – Introduction to surfactants

Before we talk about the types of cleansers, let’s first discuss what makes cleansers work? And the simple answer is, surfactants.

Surfactants are molecules with two portions: a hydrophilic head drawn to water, and a lipophilic tail, drawn to oil. Surfactants can remove oily substances from your skin because the tails binds to oil and dissolves them, while the heads allow the washing away with water. During cleansing, surfactants form micelles – external hydrophilic groups surrounding an internal lipophilic pocket. These micelles surround oily substances, such as sebum, dispersing the oil in water for removal and rinsing.

Have you experienced that taut/tight feeling your skin can get right after cleansing? One of the most common reasons is the surfactants in your cleanser. Surfactants are unable to differentiate between the skin’s important components (i.e. proteins, natural moisturizing factors [NMF] and lipids) and foreign substances, so both can removed from the surface of the skin. Therefore, cleansers can keep our skin squeaky clean, but may cause damage to our skin.

Luckily for us, not all surfactants are created alike! Some are harsher than others, while others are gentler and less irritating. One of the determinants for this is the charge of the surfactant.

Let’s briefly discuss four types of surfactants based on their charge (positive or negative): anionic, cationic, amphoteric, and non-ionic. The charge is present on the hydrophilic side, while the lipophilic side does not have a charge. It has been shown that cationic and anionic surfactants have the highest likelihood to disrupt the skin barrier and cause irritation; amphoteric is less likely; and non-ionic is the least likely. I’d also like to add that surfactants can be used as detergents  (bubbly, foaming, cleansing-focused ingredients), or emulsifiers (non-foaming ingredients e.g. creams, lotions, oil cleanser), as you will see below.

1. Anionic surfactants (anion: negatively-charged molecule)

These surfactants have a strong negative charge, making them very effective detegents in cleansers. The most common anionic surfactant is soap. One other popular one is the synthetic detergent or “syndet”, sodium lauryl sulfate (SLS). Generally speaking, these surfactants lather well and produce a lot of foam, but tend to be harsh and have a high tendency to cause irritation.

2. Cationic surfactants (cation: positively-charged molecule)

These are also very effective but extremely harsh, seen frequently in household cleaners. Common ingredients are benzalkonium chloride and cetrimonium bromide. Cationic surfactants may have antimicrobial properties, so these could be present in medical or prescription cleansers.

3. Amphoteric surfactants (have both positive and negative charge)

These surfactants are milder and less irritating than the single-charge anionic and cationic surfactants, so these are popular in facial cleansers and gentle shampoos. Common amphoteric surfactants are cocamidopropyl betaine and sodium cocoamphoacetate. These ingredients tend to foam less than the other surfactants.

4. Non-ionic surfactants (no charge)

In the skincare world, these surfactants are often seen as emulsifiers (non-foaming ingredients e.g. creams, lotions, oil cleanser). Common ingredients include the polysorbates, the sorbitans, the PEGs, and the laureth-[number]s, etc.

In summary, we identified four types of surfactants: anionic, cationic, amphoteric, and non-ionic. In terms of foaming detergents, we usually see anionic (more harsh) and amphoteric (less harsh) surfactants, while cationic surfactants can be used for their anti-microbial properties. Non-ionic surfactants are common as emulsifiers. Cleansers can have one surfactant or multiple surfactants.

Clearly, the wrong cleanser can cause skin to be dry, dehydrated and irritated over time. A good cleanser is able to remove unwanted substances while not damaging the skin barrier. Now that we know what might be going into our cleansers, let’s discuss a few types of cleansers.

What are the types of cleansers?

There are many different types of cleansers available in the market unique compositions and specific skin benefits. Let’s discuss the two major types of cleansers:

  1. Soap – one of the oldest personal care products in history. As abovementioned, soap is a simple anionic surfactant that lathers extremely well, but has a high likelihood of disrupting the skin barrier. Soap is used loosely to refer to any cleanser; however, this is not correct as soap denotes a specific chemical entity. Soap is created by combining a plant or animal oil with a highly alkaline ingredient like lye (sodium hydroxide) resulting in a fatty acid salt with detergent properties. That alkaline ingredient is crucial to the soap-making process, and this is why soap or soap-based cleansers tend to have high pHs (9-10). The high pH causes swelling of the stratum corneum (the protective outer layer of the skin), allowing deeper penetration of the soap into the skin, potentially causing irritation and itching. The soap also binds to stratum corneum proteins which reduces the ability of the skin proteins to hold water.
  2. Synthetic cleansers – also called synthetic detergents, or syndets, mix anionic and/or amphoteric surfactants with a number of other mild ingredients to create a gentler cleanser than soap. In general, these are formulated to have a low pH (5.5 – 7) and don’t often foam up as much as soap-based cleansers, but have been shown to penetrate the skin less, preserving its natural barrier function.

Solid/bar or liquid cleanser?

Not all solid cleansers are “true” soaps! Some have gentle surfactants and are enriched with moisturizers like glycerin, lanolin, or natural oils.  Check the ingredient list to be sure! Just because a cleansing product is packaged as a bar does not necessarily mean that its ingredients will leave your skin tight and dry. Liquid cleansers often have water as the primary ingredient, mixed with syndets (e.g. sodium lauryl sulfate and cocamidopropyl betaine) and moisturizing ingredients (e.g. petrolatum, vegetable oils, or shea butter), doing the dual action of cleansing and moisturizing.

What should I look for in a cleanser?

. Gentle surfactants

It is best to avoid cleansers with harsh surfactants that may damage the outer layers of the skin. For example, Fatty Acids (Myristic Acid/Palmitic Acid/Oleic Acid) + Potassium Hydroxide (or Sodium hydroxide) are fatty acid/potassium hydroxide combinations commonly seen in a soap-based cleansers. These have a high pH (8-10). Sodium Lauryl Sulfate (SLS) is a popular surfactant that provides good foam. However, studies have shown that this surfactant can interact with skin proteins and cause irritation. This does not mean we should avoid all SLS cleansers! If properly formulated, it can be an effective, budget-friendly option for those who do not have sensitive skin. If you are concerned about the potential of irritation from your cleanser, it is best to look for blends of milder surfactants like the following:

Sodium Laureth Sulfate (SLES): often paired with SLS; SLES is the milder of the two surfactants.

Cocamidopropyl betaine: derived from coconut oil; a common co-surfactant used in gentle, low pH cleansers.

Sodium Lauryl Sarcosinate: made from the salts of amino acids; can provide mild conditioning properties and is one of the most commonly found mild surfactants used in cleansers.

Sodium Cocoyl Isethionate (SCI): also derived from coconut oil, one of the mildest surfactants,; recommended for those with really dry, irritated skin but usually more expensive than other surfactants.

Research studies have shown that mixtures of surfactants such as sodium laureth sufate (SLES) in combination with cocamidopropyl betaine, among others, compared to a single surfactant, make for gentle cleansers. As discussed, surfactants assemble into spherical micelles in solution. Smaller-sized micelles penetrate easily into the skin and have the potential to cause more irritation than larger ones. Mixtures of surfactants are thought to form larger micelles, hence have a lower chance to induce irritation.

 Pro tip: Look for mild surfactants listed in the top half of the ingredient list. Multiple surfactants in the ingredients list of a cleanser is a good sign.

. Moisturizing ingredients

Cleansers that contain moisturizing substances help replace what was stripped from the skin during the cleansing process and prevent the cleanser from removing as much. This is important because the retention of water and maintenance of a hydration balance in the superficial skin layers ensures the skin’s elasticity and flexibility. Check the ingredient list for hydrating ingredients (e.g. glycerin, lanolin, olive oil, cocoa butter) which can help minimize irritation potential.

Pro tip: Cleansers with moisturizing ingredients protect the skin from being stripped of essential factors.

. Low pH

The skin’s pH is acidic (around 5), and many of the biochemical reactions occurring in the skin only work within a narrow pH range. High pH cleansers can alter skin pH for long amounts of time, preventing the skin from repairing itself and reducing its flexibility.

Pro tip: Cleansers with a low ph (<6) are ideal.

. Fragrance-free

Fragrance ingredients are one of the most common causes of contact reactions. These reactions are commonly seen in women with facial or hand eczema and those with a history of reactions to fine fragrance or scented deodorants. To avoid the possibility of irritation or allergies to fragrance mix, it is best to use a fragrance-free cleanser.

Pro tip: Look for cleansers that say “fragrance free” or “hypoallergenic”, particularly if you have dry, sensitive skin.

How long should cleansers stay on skin?

The ability of the cleanser to rinse completely from the skin is important. All soaps and syndets have the potential to be irritating so they must not remain on the skin any longer than necessary.


Skincerely yours,

Dr. Mara Evangelista-Huber

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