Debunking Myths: Walnut Shell and the Science of Gentle Exfoliation

On this page

• The micro-tear myth was never about the walnut
• Particle engineering is everything
• Applications go far beyond the face scrub
• Sustainability is built in – not bolted on
• The negative perception is now a formulator issue, not a consumer one
• Final thoughts

Remember how some 10 years ago, walnut shell scrubs became the "bad guy" of skincare? The class-action against Unilever's St. Ives helped cement that reputation. Their scrub was supposedly "unfit to be sold or used as a facial scrub." The lawsuit was ultimately dismissed in 2018 — when plaintiffs were unable to substantiate micro-tears as a defined and measurable injury — but the narrative had already stuck. Then in 2019, Kylie Jenner faced backlash after launching her walnut face scrub. The perception only hardened.

What's interesting is how long that idea has stayed in place, even as formulation science has evolved quite a bit.

The micro-tear myth was never about the walnut

The original backlash against walnut shell scrubs was less about the ingredient itself and more about how it was processed — and how consumers were using it.

As Ewelina explained during the webinar:

"The original backlash was against the uncontrolled or irregular particles used with high frequency, not necessarily against the walnut kernel per se. It was about: how was it processed? The problem was never the walnut as a plant — it was poorly controlled particle engineering plus consumer overuse."

Helen Cantrell added important historical context: the original St. Ives formula actually used apricot shell, not walnut. Apricot shell grinds into more cubic, angular particles with sharper edges. When Eco-Shell introduced walnut shell into that formula, they brought with them a patented grinding process specifically designed to round the edges — creating what Helen calls a "pearlized" particle.

"We have an innovative grinding process that actually rounded the edges of the particle to make our walnut shell more pearlized. We've been doing this for over 30 years now, and we have sort of perfected the shape and the distribution."

The negative reputation, in other words, stuck to the wrong ingredient for the wrong reasons.

Particle engineering is everything

Zoom into the science, and the "natural vs. chemical" debate starts to feel overly simplistic. What actually determines whether an exfoliant is safe or harsh comes down to particle engineering: size, shape, hardness, and loading level.

Helen walked through the breadth of Eco-Shell's size range — from coarse 3560 particles suited for foot scrubs, to ultrafine minus-325 powders approximately ten times finer than table flour — suitable for masks, foundations, and sensitive skin formulations.

"We can go aggressive for a foot scrub and we can go ultra-fine for powder foundations, lip exfoliants, sensitive skin formulations. It really is depending on what you're trying to build."

The particle sizing system itself follows US sieve standards: a "6100" grade means particles pass through a screen with 60 to 100 holes per lineal inch. The higher the number, the finer the particle.

Critically, Eco-Shell's pearlization process — their proprietary multi-stage milling method — removes the sharp edges that plagued earlier formulations. As Ewelina put it:

"When you think about Eco-Shell, think about the pearls — walnut shell pearls. They are not harsh. Some of them are so almost like a micro-fine powder that you wouldn't even feel it on your face."

Formulation context matters too. Mateja noted:

"It's never really one ingredient. You need to look at the entire formulation. A gel with a walnut shell is going to perform very differently to a high viscosity cream with a velvety, sensorial texture."

Applications go far beyond the face scrub

One of the most surprising takeaways from the webinar is just how many formats and product categories walnut shell can serve.

Because walnut shell is surface-absorbent (it doesn't soften or dissolve like sugar or salt), it remains structurally intact in the formula. It accepts colorants, suspends across a wide range of bases — gels, creams, oils, bar soaps, and powders — and can be custom-milled to a brand's exact particle specification.

Applications discussed included:

• Scalp scrubs — including emerging medicated formulations for mite removal in children
• Toothpaste — as a natural polishing agent replacing talc, already in use in multiple international markets
• Powder foundations and lip exfoliants — using the ultrafine grades
• Clay masks and complexion products — using flower-grade powders
• Industrial hand scrubs — using heavier loading with fine-to-medium particles
• Skin barrier-friendly facial formulations — using finer grades for sensitive or eczema-prone skin

Helen also shared a memorable example that illustrates the ingredient's versatility:

"There's a strawberry scrub — it smells like strawberry, it looks like it has strawberry seeds in it, but it's a body scrub in gel form. What they've done is put in a kiwi seed to make it look like strawberry. But the workhorse doing the exfoliation? That's walnut shell."

Sustainability is built in – not bolted on

Eco-Shell's sustainability story isn't a marketing retrofit. It's the origin of the company itself.

As Helen explained, EcoShell was founded in 1995 precisely to solve a waste problem. The family business — which spans 16,000 acres and sources from 400 walnut growers across California — was generating enormous volumes of walnut shell as a byproduct of cracking walnuts for the kernel market. Before EcoShell existed, that shell was going to landfill or being burned in fields.

"We were sustainable before sustainability was a thing in the market. EcoShell came to fruition in 1995 out of the need to upcycle the waste materials coming from our cracking facility."

Today, Eco-Shell processes over 80,000 tons of walnut shell annually — year-round, from a single harvest window. The walnut shell itself carries an impressive certification portfolio: Ecocert (including China), Leaping Bunny, and is free from pesticides, heavy metals, and chemical processing. Because it's not chemically derived, it falls outside standard SDS chemical requirements.

Helen also addressed the biodegradability question — a genuine concern in a post-microplastic world:

"It is definitely a biodegradable product. It flows very well. It's biodegradable and septic-safe in sewer systems — that's exactly the reason we've moved away from microplastics to naturals."

The Negative Perception Is Now a Formulator Issue, Not a Consumer One

Perhaps the most striking observation in the webinar came when addressing whether the walnut shell stigma persists with consumers today.

Helen was direct:

"I think more of the negative perception is not a consumer issue — it is a formulator's issue at this point in time. If you look at the market today, there are many different wellness scrubs on the marketplace. The consumer is buying them."

Ewelina agreed, pinpointing the root cause:

"It was guilty by association. The ingredient concept was never the problem — it was formulation and processing. And that bad notation has been kept alive by 'Google research' and, frankly, by competition."

Helen noted that since January alone, Eco-Shell had been targeted in six or seven major online posts attacking walnut shell as aggressive or comparable to microdermabrasion.

The remedy, the panel agreed, is education: helping formulators understand the distinction between poorly engineered particles of the past and precision-milled, pearlized particles of today.

"It ticks so many boxes — for the product developer, for the cosmetic chemist, for the marketer, for the consumer," said Ewelina. "It's a no-brainer."

Final thoughts

The walnut shell conversation is a useful lens on something broader: how quickly a narrative can calcify in the beauty industry, and how long it can outlast the science that should have updated it.

As formulation science has matured, so has the ingredient. Pearlized particles, precision size distribution, custom milling, and rigorous certifications all point to a material that deserves a second look — particularly from formulators still avoiding it based on headlines from a decade ago.

If you're a formulator interested in trialing Eco-Shell materials, click here to request your samples and quotes on Covalo.

This article is based on the Covalo x Eco-Shell webinar featuring Mateja Weber (cosmetic scientist), Ewelina Aiossa (Founder, Topical Skin), and Helen Cantrell (Director of Sales & Marketing, Eco-Shell). Watch the replay here.