64 JOURNAL OF COSMETIC SCIENCE
A common in vitro assessment of dermal irritation known as a Zein test determines the
percentage of the water-insoluble corn protein Zein that is denatured when exposed to
irritants. Zein is representative of protein in the human epidermis, that can be denatured
and thus solubilized in an aqueous surfactant solution. The experience of having “squeaky
clean” skin after applying skin cleaning productions is typically the result of surfactants
penetrating and damaging the skin barrier (stratum corneum) by multiple mechanisms one
example is causing damage to the skin protein keratin.26 This can be particularly irritating
to more sensitive skin with a thinner epidermal layer, particularly in some areas of face such
as the scalp and eyelids.27 The OFS surfactant sodium dodecanoyl methylfuran sulfonate
was observed to dissolve significantly less Zein (1%) compared to all other surfactants
tested, indicating a milder effect consumers prefer in personal care products (Figure 4B).
In addition to providing a milder and more stable ingredient for personal care, OFS
surfactants have demonstrated broad ingredient compatibility, with viscosity building
agents, preservative systems, fragrances, moisturizers, and numerous other common
personal care formulation ingredients. For the results described herein, compatibility is
defined as the ability of the ingredients to be combined and fully dissolved all ingredients
must remain dissolved in solution, without formation of precipitate or phase separation,
for a minimum of one week at room temperature to be considered compatible. With the
guidance of expert formulation consultants, we have developed fully functional personal
care product prototypes featuring OFS surfactants.
Versatility in cosurfactant selection for viscosity building has remained a major focus in
formulation testing with OFS. While most surfactants in the OFS platform do not thicken
with salt alone, a range of rheological properties suitable for personal care products can
be accessed through the use of amide and amphoteric cosurfactants, and is further refined
with the addition of salt in the range of 1–3 wt%. In particular, cocoamidopropyl betaine,
lauroamphoacetate, dimethyl lauramide, glyceryl caprylate, cocamidopropyl hydroxysultaine,
and cocoamide MIPA were among the cosurfactants found to be compatible viscosity
building systems for OFS surfactants, with ingredient loadings in the range of 3–10 wt%.
Polymeric thickeners, including naturally derived hydroxypropyl starch, xanthan gum, and
hydroxyethyl cellulose are also compatible, with typical loadings of 3–6 wt% starch or 0.1–2
wt% gum/cellulose to thicken solutions containing 5–10 wt% OFS and 1–3 wt% salt.
While the accessible viscosity ranges varied with the selected cosurfactant or polymer,
formulations generally achieved consistencies consumers prefer for body wash and shampoo
Figure 4. Hard water stability (A) and Zein skin irritation test results (B) for 0.5 wt% anionic surfactant
solutions. Hard water stability is defined as the concentration of calcium salt that induces surfactant
precipitation. Higher percentages of remaining Zein protein indicate less dermal irritation.

65 Oleo-Furan Sulfonates
products (5,000–20,000 cps) with a ratio between 1:1 and 1:2 of OFS to cosurfactant.
The most favorable consistencies for body wash gel formulations were observed with
5 wt% OFS, 10 wt% cosurfactant, with the addition of 1–3% salt as needed. Notably,
compatibility with cocamidopropyl betaine, one of the most commonly used cosurfactants
in personal care products featuring SLES, positions OFS as an ideal drop-in replacement
to reduce dioxane content without sacrificing product performance. Figure 5 provides an
overview of the versatility in product types for which we have achieved targeted thickening.
While all thickening systems suggested can be prepared to have a gel consistency in the
aforementioned viscosity range, the surfactant and cosurfactant loadings can be tailored to
specific applications. This ranges from products such as shampoo and body wash commonly
formulated to be highly cleansing with large amounts of lather containing 10–20%
surfactant loadings, for which we incorporated 4–10% OFS with 8–10% cosurfactant,
to products such as facial cleansers formulated to have less foam and a creamy texture
incorporating 10% surfactant loadings, for which we incorporated 5% or less OFS with
polymeric thickeners.28
To achieve optimal sensory experience and facilitate proper skin care, we have demonstrated
OFS to be compatible with a variety of moisturizers and emollients typically at use levels
between 0.5 and 2 wt%. Examples include aloe vera and honey concentrate, which have been
reported to provide benefits to the health and resiliency of skin with topical application.29
Gels prepared with hydroxypropyl starch have been found to exhibit more pleasing textural
attributes and are more tolerant to cold storage and freezing and thawing improve texture.30
Low loadings (0.1–0.5 wt%) of hydroxypropyl starch were incorporated into OFS body
wash prototypes to provide the reported richer, velvety texture while avoiding the tacky or
sticky texture often associated with polymeric ingredients at higher loadings.
A potassium sorbate and sodium benzoate preservative system is highly effective for
preventing microbial growth in OFS formulations, as well as for maintaining consistent
product appearance, viscosity, and sensory experience over time. For shelf-life testing,
loadings of 0.28 wt% and 0.14 wt% for potassium sorbate and sodium benzoate were
used, respectively, for preserving test body wash formulations. Shelf life of the formulated
product was determined as maintaining an identical appearance and viscosity to the product
immediately after preparation, without phase separation or ingredient precipitation.
By these metrics, body wash formulations featuring OFS (both prepared as liquids and
Figure 5. Overview of OFS surfactant compatibility with viscosity building agents across a range of
formulation types, including polymeric and micellar thickening agents. Viscosities were measured with a
rotational viscometer at ambient temperature with a rotation rate of 30 rpm and applied torque in the range
of 34.9 and 98.9%.