Exfoliating Agents: Selection and Formulation Tips

Exfoliation: Importance & Different Ways to Exfoliate

Exfoliation is a cosmetic technique aimed at improving skin appearance by removing dead skin cells from the surface of the skin.

It is the process by which the dead skin cells which accumulate on the topmost layer of skin or stratum corneum are removed or cleared away for the new layer of skin cells to come to the surface and grow.

It is also designed to:

Aid rejuvenation of the skin
Prevent undesirable conditions such as acne scarring or ingrown hairs
Hide fine lines
Add glow and luster to the skin

When you exfoliate, you are mildly abrading your skin and removing the surface layer of dead cells. Removing excess dead skin cells can reveal the younger and healthier-looking skin underneath.

Exfoliating cleansers, scrubs and skin polishes are popular among consumers who look for deep cleansing. Exfoliants are gritty solids of varying particle size which provide sensory signals of cleansing when rubbed into the skin. The abrasive nature of these particles suspended in a suitable base provides a smooth after-feel.

Why is Exfoliation Important?

Exfoliation allows for cell turnover, which, in essence, is the removal of the old to make way for the new. This is also a way to protect the skin and assist it in the anti-aging process. The process goes on constantly, and as the skin cells grow old & die and become saturated with keratin.

As people get older, the process of cell migration from the lower layers to the topmost layers becomes uneven and can even slow down, causing the skin to look dull, uneven, and show signs of wrinkling.

Proper and regular exfoliation allows these dead cells to be removed on a more complete and efficient basis.

This keeps the skin healthy and younger-looking because it promotes more even cell turnover by keeping the newer skin cells in a constant state of motion and preventing the skin from looking and feeling old.

How Does Exfoliation Happen?

Exfoliation happens via 4 different ways:

By itself
With the use of scrubbing particles
With the use of chemical exfoliants
- Some of the most common are the alpha hydroxy acids such as glycolic, salicylic or lactic acids.
- At higher concentrations, these ingredients act as chemical peels and actually remove to topmost layer of skin.
- A chemical peel goes far below the epidermis into the dermis. This method of going deep into the skin stimulates new cell growth on a more rapid level, the same level as when the skin was younger and healthier.
By microdermabrasion also removes the topmost layer of skin cells

Mechanical Exfoliation with Abrasive Materials

Extreme Cases of Exfoliation

The cosmetic procedures dermabrasion and microdermabrasion are both extreme cases of exfoliation where the surface layer of skin is removed as if by sanding.

Dermabrasion:

It is a skin resurfacing technique that is used to treat facial scarring.
Earlier it was used predominantly to improve acne scars, chickenpox marks, and scars resulting from accidents or disease.
Nowadays, dermabrasion is also used to treat deep facial lines ad wrinkles, severe sun damage, pigmentation disorders, and certain types of skin lesions.

Microdermabrasion:
- It is similar to dermabrasion, but as its name suggests, it uses tiny crystals to remove the surface skin layers.
- Microdermabrasion is now possible using home kits that use a vibrating foam applicator to massage a moisturizing cream containing aluminum oxide crystals on the surface of the skin.

Chemical Exfoliating Agents: Types & Examples

Exfoliation is most often achieved through either mechanical or chemical means. Chemical exfoliation involves the use of acids or enzymes to help dissolve away either the ‘glue’ that holds skin cells together (BHA and Enzyme action) or the actual skin cell itself (AHA’s).

Aged cells that remain attached for longer than necessary can give the skin a patchy, grey look, and can also trap dirt underneath them making comedones more likely. Gently removing these cells has an immediate brightening effect on the complexion while also leaving it feeling smoother and cleaner.

Chemical exfoliants include scrubs containing salicylic acid, glycolic acid, fruit enzymes, citric acid, or malic acid, which may be applied in high or low concentrations as recommended by the dermatologist.

AHA’s or Alpha Hydroxy Acids

AHA’s or Alpha Hydroxy Acids can be quite powerful due to their ability to dissolve the whole skin cell, so care must be taken in their selection, formulation and application.

Generally speaking –

a. The smaller the AHA molecule the more mobile it is

b. The lower the pH the faster it can travel across and through the skin and

c. The higher the concentration of the AHA in your formula the more complete the action across the skin surface.

Glycolic acid at a pH of around 3 in a concentration of 10% or more is about as strong as a cosmetic product gets!

Being acidic in nature, AHA’s do pose for formulator, some compatibility challenges including being un-suitable for use with acrylate type thickeners such as carbomers. There are also some difficulties when working with AHA’s in organic formulations as some organic certification bodies don’t allow the use of sodium hydroxide to adjust the pH upwards to a safe level.

Acids can also react with metal oxides (iron oxides) shifting their color and will reduce carbonates (pearl extract, sodium bicarbonate) to their salt plus water and gas (carbon dioxide).

One other important point to note when working with AHA’s is the fact that the use of formulations containing AHA’s will leave the skin more sensitive to sunlight. There are specific laws regulating how this risk is worded to the public, but as a formulator, care should be taken to balance the benefits of the AHA product with the risk of leaving premature skin-cells exposed to UV.

BHA salicylic acid

The BHA salicylic acid has a more specialized action dissolving away the glue that holds skin cells together in sheets.

Salicylic acid use is restricted in cosmetic formulations due to its potential to be toxic within the body, and as such, we stick to concentrations of 2% or lower for adult formulations.

Salicylic acid is best formulated into the oil component of a formula, or in an oil-free environment can be pre-neutralized to a salt with sodium hydroxide before addition.

Enzymes

The final class of chemical exfoliants, enzymes are attractive to the formulator as they look much more natural on an INCI listing! The two of the more common enzymes used in cosmetic formulations are:

Bromelain and
Papain

These work in a similar way to the BHA by dissolving away the glue that binds the cells together. While these ingredients sound the best in terms of naturalness and purity, they are the most likely to cause a skin reaction.

Enzymes are biologically active, and as such, these are not a good first choice for people with damaged or aged skin. The other down-side of enzyme technology is their bio-burden.

AHA and BHA's, if formulated into a stable base, are unlikely to raise the risk of a formula, whereas enzymes can due to their reactivity (potential to degrade) and their carbon content.

These factors can be successfully formulated around, and enzyme exfoliant products do have their place in the cosmetic market but it is important that the formulator and brand owner doesn’t overlook these points when putting a product together.

Physical Exfoliating Agents: Types & Examples

On top of regulation & marketing considerations, you need to pay attention to the following criteria when selecting your exfoliants:

Particle Size: Smaller particles will be preferred in facial applications, while larger particles are best suited for body scrubs.
Level of Exfoliation or Particle Abrasiveness: It depends on the hardness of the material used, the shape & edge of the particles.
The sensitivity to oxidation & microbial issues as well as other formulation incompatibilities.

Plastic Microbeads

Up to now, plastic microbeads have largely dominated the market. There are four main reasons why a brand might have come to decision to use plastic microbeads in a cosmetic product:

They are cheaper than pretty much every other option. Cheaper by a huge margin, quite possibly only 1/10th of the cost.
They present a much lower micro bio-burden than the vast majority of their natural equivalents, especially the nutshell equivalents.
Nobody is allergic to plastic.
They can be colored, shaped, sized, and weighted to order - hard or soft, big or small.

But times are rapidly changing, and what was once a great idea now looks negligent and completely unappealing. Governments around the world have spoken, bringing in legislation to ban these tiny bits of plastic from cosmetic products, products that end up directly in our waterways and beads that ultimately wash into our seas.

There are plenty of alternatives, each having pros & cons. The challenge is to achieve microbially stable formulations with natural particulates without using ‘strong’ preservatives such as the parabens and formaldehyde donors.

» Related Read: Choosing Greener Alternatives to Plastic Microbeads

Jojoba Beads

Jojoba beads were early onto the market and remain popular, with many manufacturers now offering exfoliants based on Jojoba esters or hydrogenated jojoba oil.

Jojoba beads have many advantages in a cosmetic product being naturally moisturizing and skin-compatible while also having a high tolerance to oxidation making them very stable.

The beads are perfectly spherical for a gentle scrub with a low irritancy potential, which is ideal for incorporating into products for sensitive, aged, or problem skin. However, jojoba isn’t the most cost-effective oil and as such jojoba beads won’t suit every application.

Lower Cost Alternatives to Jojoba Beads:

Ecobeads® from Floratech – A blend of jojoba, palm and candelilla. This makes the blend more cost-effective, but the palm content may raise question marks amongst the market even if it is sustainably sourced (trust in the supply chain for Palm remains relatively low).
Castor Oil from Worlee
Rapeseed Oil derivative from Koster Keunen

Polylactic Acid (PLA) Beads

Another interesting exfoliant is the Ecoscrub® from Micro Powders. This is based on polylactic acid, a biopolymer that is usually manufactured from corn or sugar-beet.

Bioplastics is a term that applies to both biodegradable petroleum-based plastics and plant-derived plastics that aren’t necessarily biodegradable as well as mixtures of the two.

The biodegradability of the Ecoscrub® is unknown, but from a sustainability perspective and an investment in green technology angle, this is certainly worth a look.

Natural Particles

Natural particulates allow the formulator to really develop a story for the brand. Many of these plant-derived scrub agents come from sources known for their:

Antioxidants (Grapeseed, Olive, Cranberry)
Skin stimulating effects (Coffee, Guarana)
Moisturizing power (Oats, Sugar) or
Antimicrobial properties (Tea Tree, Sandalwood)

a. Grains

Rice bran and oats come under this category of exfoliants. These are known to offer low to medium exfoliation. These exfoliating agents can be found in a powdered or fine particulate form.

Oxidation: These agents offer a medium to low risk of oxidation.
Microbial Risk: Also, their high surface area and carbon content makes them prone to microbial issues.

b. Fibers

Depending on your choice of fibers, you can achieve various level of exfoliation. These can be found in fibrous or irregular forms.

Examples: Sandalwood and loofah

Sandalwood (L) and loofah (R)

Oxidation: These exfoliating agents may oxidize
Microbial Risk: Like grains, fibers are also vulnerable to microbial attacks due to their high surface area and carbon content.
Other Risk Factors: It can be difficult to suspend because of their irregular weight and surface area.

An interesting alternative is Celluloscrub™ (cellulose Acetate) from Lessonia. This scrub is less spherical and more granular than the waxy beads and as such, is more abrasive.

Although natural, this modified material presents a lower bio-burden than Loofah or Sandalwood. It can usually be preserved in a cream or gel base using the newer generation preservatives.

c. Botanical

Like fibers, botanicals can deliver various exfoliating power. These are mostly irregular in shape.

Oxidation: Botanicals are also prone to oxidation
Microbial Risk: Their high surface area and high carbon content make them sensitive to microbial issues, even with Tea Tree.
Other Risk Factors: They may pose an allergy risk. These exfoliants may discolor the formulation too.

Examples: Hibiscus, Tea Tree, Guarana and Bitter Orange.

(Left to Right) : Hibiscus, Guarana, Tea Tree, Bitter Orange

d. Nut Shells

Nut Shells like Walnut, Argan, Almond, etc. have a high level of abrasiveness.

Walnut (L), Argan (C), Almond (R)

These exfoliants are irregular in shape with rough edges.

Oxidation: Nut Shells are relatively stable.
Microbial Risk: When compared to others, these exfoliants are highly prone to microbial attack.
Other Risk Factors: They also a pose potential allergen risk.

e. Soft Minerals

This class of natural exfoliants offer soft to medium exfoliation to the skin. Pearls and sodium bicarbonate belong to this category. Like grains these are powdery or very fine granules.

Microbial Risk: They have a relatively low microbial risk. Pearls could pose a risk for spores, but the high pH of bicarbonate makes it less risky.
Other Risk Factors: When in contact with water, they may partially or wholly dissolve. Also, their use is not recommended in acidic environment – they will react.

f. Hard Minerals

Diamond, Pumice, Sands are some hard mineral-based exfoliating agents.

Volcanic ash (L), Pumice (R)

These deliver very high exfoliation to the skin. They are best suited to heavy-duty or deep-cleansing applications, but their chemical non-reactivity and lack of sting-factor would mean they shouldn’t be discounted from every-day formulations.

Physically these could be crystalline to rough depending on how the particulates have been ground. Hard minerals may contain very sharp edges.

Microbial Risk: They have a relatively low microbial risk but may introduce dormant mold spores if not stored carefully.

g. Salts

Salts, as we know, are crystalline, relatively regular, although rock salts do contain smaller, irregular granules. Salts as exfoliants can offer medium to high abrasiveness to the skin.

Examples: Himalayan Rock Salt, Sea salt and Magnesium

Microbial Risk: Salts are less prone to microbial attack and can act as anti-microbial in some formulations.
Other Risk Factors: Salts sting open wounds & dry out the skin. As exfoliants, salts offer limited formulating freedom.

h. Sugars

Sugars are almost like salts in terms of appearance and exfoliation properties.

Examples: Brown, white, coconut, palm sugars

Microbial Risk: They pose very low risk of microbial contamination.
Other Risk Factors: Being moisture sensitive, sugars can give a sticky feeling and low formulating freedom.

i. Seeds and Kernels

Seeds of Strawberry, Apricot, Rosehip, Grapeseed, Olive, Cranberry, Lotus are used as exfoliants too.

strawberry seed

(Lelf to Right) : Strawberry, Rosehip, Cranberry, Grapeseed, Lotus

These deliver low to medium level of exfoliation to the skin. They are irregular in shape, have a large surface area to volume and rough edges.

Oxidation: This class of exfoliating agents is prone to oxidation.
Microbial Risk: They are highly vulnerable to microbial degradation due to surface dynamics and high carbon content.
Other Risk Factors: These offer natural coloring & odor, which can discolor the formulation. Being natural, these can pose allergen risk to the user.

Non-aqueous & Aqueous Exfoliating Cleansers

Consumers recognize the vital role of skin in overall health. Exfoliation is the step most people skip in their weekly skin care routine, but a great majority of consumers perceive an almost immediate difference, if they start properly exfoliating their skin.

Exfoliant particles by nature are abrasive, and have a potential to damage the epidermal layers, produce irritation and aggravate some dermatological conditions such as Acne. This is because the gritty particles can break the walls of closed comedones beneath the stratum corneum and triggering an inflammatory process.

Scrub products, also called skin or body polishes, are a unique category of cleansing tools called Exfoliating Cleansers. They focus on:

Cleansing
Conditioning and
Treating

Scrubs have strong consumer appeal and are perfect for removing makeup, skin debris and dirt, leaving the skin with a fresher, smoother and more translucent look. Safety issues sometimes limit their use.

In general, scrub performance depends on the water-soluble or water-insoluble abrasives used in a scrub product.

An additional benefit is the treatment of skin with conditioners such as minerals, natural oils, emollients, vitamins, antioxidants, anti-aging ingredients and other nutrients.

Mild gentle scrubs contain natural botanical exfoliants suspended in a base of essential, often exotic oils and fragrance. The essential oils work toward a deep down clean, while the small natural exfoliating grains smooth and rejuvenate skin texture.

Non-aqueous-based Exfoliating Cleansers

They provide complete cleansing while also focusing on skin conditioning and treating.

Water-soluble abrasives, such as brown or white sugar and salt, are generally used in non-aqueous-based formulas. Sugar is a natural anti-microbial agent that does not spoil over time.

Salt usually makes a slightly grittier product than the sugars, and it may also be drying for those with dry skin. Salt scrubs are generally not recommended for facial skin, but sugar scrubs are excellent choices. These abrasives are suspended or immersed in a wide range of carrier oils.

In salt scrubs, besides sodium chloride, other salts such as magnesium, calcium or potassium chloride and dead sea salts are used in the preferred particle size range of 150 - 800 microns.

Commonly used are natural or essential oils, esters, mineral oil, iso-paraffin, silicones and glycols.

Glycols are not suitable for sugar scrubs. The choice of the oils depends on the products end-use for a specific skin type.
Silicones are not used in products marketed under the natural umbrella. At least fifty natural oils used in oil-based scrubs have been identified. The choice of the oils depends on whether the product is formulated for normal, dry or oily skin.

A popular category of non-aqueous scrubs is Warming Scrubs.

These exfoliant cleansers feature a warming technology that instantly heats up when mixed with water to remove pore-clogging residue.
The warmth helps the scrub provide a deeper cleansing, deep down-to-the-pores, minimizing the pore appearance and leaving the skin feeling soft and smooth.
These formulations are often glycol based with zeolites. Glycols commonly used are PEG-8, ethoxydiglycol and butylene glycol.

Warming body scrubs unlike salt scrubs are less irritating and suitable for dry facial skin.

Besides sugar and salt, there are products that use unique ingredients such as: Almonds, Oats, Orange Peel, Rose Powder, Pecan Powder, Nutmeg Powder, Clove Powder and other natural ingredients.

Aqueous-based Exfoliating Cleansers

These traditional scrubs continue to enjoy an upswing in the growing spa market. The soft massage beads dissolve as the cleanser lathers to gently polish away dull, lifeless skin to reveal its natural glow. These scrubs also have:

Typical example is Dove Gentle Exfoliating Daily Facial Cleanser.

The basic types of aqueous formulas are gels, creams, pastes or thick lotions.

Paste-like formulas are mainly based on sodium stearate/stearic acid mixtures, which suspend the abrasive particles.
Gel-like formulas are anionic surfactant systems with additional gelling agents for suspending the abrasives.
Emulsion type is a thickened cleansing emulsion, which is capable of suspending abrasive particles. The abrasives used include:
- Polyethylene beads
- Pumice
- Nylon powder
- Polypropylene
- Cellulose beads

Natural shells or seeds include walnut, almond or cottonseed shells & jojoba beads; natural fibers such as Loofah (fibers from exotic cucumber) & Sisal; seeds such as sunflower-, grape- & watermelon seed; waxes and other items include orange peel, almond and oatmeal.

Micro Powders has an extensive and innovative product range of specialty micronized waxes designed to be used as exfoliating agents which are non-irritating to skin surfaces.

Considerations for Formulating Exfoliating Particles

While physical exfoliants are less likely to give the formulator chemical problems in a formula they can be equally difficult to work with. What one is trying to do with a physical exfoliant particle is suspend it neatly in a fluid base – to hold it up against the forces of gravity. This is a challenge in itself!

Suspending Power

Viscosity (or thickening power) is not enough to hold back gravitational pull, a formula needs strength or suspending power and we measure that in its yield value – the initial resistance to flow shear applied stress. Yield value is measured in Dynes/cm².

A dyne is a unit of measure that relates centimeters, grams and seconds so the distance travelled in CM by a certain weight over a set time.

The formulator has a choice of many thickeners including a whole range of natural gums and polymers but not all of these will have the yield strength necessary to hold exfoliant particles in suspension for a 30-month shelf-life.

While the formulator can get some starting-point help from data sheets and values, getting this absolutely right for what might be quite a complex and unique formula involves experimentation, observation and quite possible a dash of centrifuge analysis!

The particle size, shape and weight of an exfoliant must be considered when selecting an appropriate suspending agent and in a mixed system it is entirely possible that one exfoliant holds while another ‘falls through the cracks’. This is one reason why some formulators choose to use two suspending agents – to form a more complex mesh structure with a synergistically higher yield.

A combination of freeze/ thaw stability and centrifuge analysis helps to short-cut the R&D process in selecting the right suspending agent.

In a cream-based formulation, the yield value is often achieved through a combination of the emulsion structure as given by the emulsifier and any structuring waxes plus a water-phase thickener. While the formulator should consider the extra burden placed on these structures by the exfoliant particles the chances of failure are much lower.

Additional Considerations

Other than yield value considerations, factors such as the exfoliant solubility, melting point, color and/or odor deserve a mention.

Some of the natural wax beads such as jojoba have a low melting point and can start to dissolve into the base if added at 40°C.
Pearl exfoliant particles will react with any acidic material in the formula and some plant-based materials such as cranberry and hibiscus may partially dissolve and discolor a formulation turning it pink!
Care must also be taken when using salt and sugar as any moisture in the formula including that from surfactants, actives or humidity can soften and deform these exfoliant particles.
The final point to consider with exfoliants either physical or chemical is preservation.

AHA’s will require a low pH, usually 4 or less to enable them to work effectively, this puts AHA formulations into a lower risk bracket microbially but doesn’t mean the product is necessarily risk-free.

Preservatives selected must be able to work at this low pH and should also avoid reacting with the acids in the formula.
In a skin care application, enzymes typically work well at pH 5-7 even though the enzymes themselves can sit in formulations with pH between 3-9. We tend to keep the formulations at pH 5-7 with enzymes to minimize the potential for irritation given that enzymes are already more likely to irritate the skin than a mild AHA. At this pH, microbial contamination is at higher risk, so a good broad-spectrum preservative plus other free-water binding and chelating strategies is wise.

Physical exfoliants are nearly always going to increase a formulations bio-burden due to the increased surface-area that is introduced.

Sometimes it is appropriate to irradiate the exfoliant before adding it to the formula in order to introduce it ‘clean’. Other times the only option is to follow a diligent whole-formula preservation strategy with chelating agent, free-water management, Good Manufacturing Practice and low-risk packaging choice to get you through.

While working with exfoliants can be challenging, if potential problems are identified and tackled step-by-step it is more than possible to produce a wide range of safe formulations for our clients. What’s more, the amazing array of choice in terms of colors, textures, aroma’s and chemistry makes our job even more exciting, artistic and rewarding than ever before.

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About Amanda Foxon-Hill

Amanda Foxon Hill

Amanda Foxon-Hill is a consultant Chemist and Science Communicator with over 14 years of experience in the global cosmetics industry. She is a writer, after dinner speaker, strategist and lecturer in all aspects of cosmetic science and runs a successful consultancy practice under the name of Realize Beauty.

Amanda’s key skills are in networking and communicating ideas and opportunities both on a business to business and business to market level. She is an advocate for green science and through her team funds research into the development of more sustainable manufacturing practices.

About Nick Morante

Nick Morante is currently a Senior Chemist at IFC Solutions (formerly International Foodcraft) in New Jersey where he works with many types of colors and additives for both the food and cosmetics industries.

He has over 40 years of experience in the formulation of cosmetics, personal care products and makeup products. Prior to joining IFC, Nick was a consultant to the cosmetics industry for over 10 years providing custom formulations for clients as well as giving presentations and seminars to various companies and organizations within the cosmetics industry providing guidance in the practical use of color in consumer products.

He is current an adjunct faculty member at Fairleigh Dickinson University’s School of Natural Sciences in Hackensack, NJ where he is an instructor in the Master of Science Program in Cosmetic Science.

Nick also spent over 30 years in Research and Development at The Estée Lauder Companies where he was both a formulator and laboratory manager in the corporate makeup and hair care departments. He was also in charge of the Color Science Laboratory where he was responsible for color measurement and spectrophotometric analysis of finished products, ingredients and human skin as it relates to color that is used in various cosmetic products, as well as developing testing protocols and methodologies for many color applications.

Nick holds a Bachelor of Science degree from The New York Institute of Technology. He has taken numerous continuing education courses in the area of cosmetic science. He is a long time member of U.S. The Society of Cosmetic Chemists and has been active both on the local and national levels having served on the executive committee for the Long Island Chapter and on the National Board, serving as Area Director and National Secretary. He has been elected a Fellow of the Society and is an instructor for the Society’s Continuing Education Program (CEP) Program in the area of color and makeup formulation problem solving and troubleshooting.

He has given many seminars and presentations worldwide as well as to the SCC, CTFA and HBA. He has been awarded numerous patents and has contributed many articles and papers and authored chapters in numerous cosmetic, technical and beauty publications and texts.

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