How Kao Corp.’s Humidity-Controlled Sunscreen Shifts the Paradigm for Climate-Adaptive Beauty

Beauty consumers are exposed to the effects of a shifting climate on many fronts; higher and lower humidity, rising temperatures, sun exposure, pollution, etc. As such, formulating products that deliver both efficacy and sensory elegance under dynamic conditions has become a key challenge — especially in the realm of sun protection. 

Bioré UV Aqua Rich Airy Hold CreamImage courtesy of Kao Corp.

Kao Corp. recently addressed this need with the launch of its Bioré UV Aqua Rich Airy Hold Cream, a sunscreen featuring a humidity-adaptive film that responds to ambient moisture. Key to the sunscreen's efficacy is the use of an agar hydrogel to encapsulate UV absorbers, in combination with high water-retention polymers. The company's approach represents a paradigm shift in how cosmetic chemists can ensure user compliance and comfort for UV defense in real-world conditions.

Here, we provide an overview of Kao Corp.'s work. In addition, Takahiro Kawamoto, an innovator in the company's skin care research department — focused on protect, care and thermo control care development — describes the science and formulation strategies underpinning this climate-smart breakthrough.

Water-Based System for Sufficient, Consistent Application

Initiating this work, Kao Corp. found through a survey that the vast majority of consumers experienced sunburn despite using sunscreen, suggesting products were not being used in sufficient amounts. An additional survey revealed that individuals in hot and humid environments found sunscreen uncomfortable to wear. 

The goal thus became to develop a product to encourage sufficient, consistent application while also improving user comfort. The refreshing sensory profile of water-based sunscreens — enabled by the company's strength in their formulation — led Kao Corp. in an o/w formula direction.

Formulating sunscreens in a water-based (o/w) system with high levels of UV absorbers poses stability concerns, however. Kao therefore incorporated agar hydrogel to encapsulate the oil-phase UV filters. 

Agar Doubles Down on Stability, Delivery

Agar, a gel-forming polysaccharide from red algae, enables the stable, uniform dispersion of UV absorbers in the aqueous phase. The capsule structure preserves the UV filter during storage and it allows for effective release upon product application, aiding even film formation and maintaining a light, fresh texture. It also makes the incorporation of various other ingredients into a water-based system easier while still maintaining a refreshing sensory feel.

"In existing water-based formulations, the addition of water-absorbing polymers deprives the emulsion of the water necessary for o/w emulsification, making the emulsion unstable," explained Kawamoto. "However, Kao's proprietary encapsulation technology stabilizes emulsification, making it possible to combine with [additional high water-absorbing polymers]."

What's more, the sunscreen was designed as a semi-solid gel at rest to ensure physical stability prior to application. Upon spreading, the agar capsules rupture and the high water-retention polymers become active, resulting in the quick formation of a uniform film. 

According to the company, instrumental rheological analysis confirmed a rapid transition in modulus upon shear, supporting desirable spreadability and the ability to apply the appropriate amount of sunscreen to the skin surface.

Mechanisms of Humidity Adaptation

Depiction of formulation combining high water-retaining polymers and agar hydrogel capsulesImage courtesy of Kao Corp.

As Kawamoto alluded to, Kao Corp. took the sensory experience a step further by also integrating high water-retention polymers into the continuous aqueous phase of the sunscreen. These polymers enable the film to adapt physically in response to changes in environmental humidity. 

"It is important to choose a polymer that can absorb and expel as much water as possible," noted Kawamoto. "In this case, we chose a polymer that excels in both water-absorbing and discharging capabilities." 

Changes in protective film thickness before (left) and after (right) being sprayed with waterImages courtesy of Kao Corp.

In high-humidity environments, the polymer network actively absorbs moisture from the air. So rather than the film becoming saturated and "tacky" — a common failure point in humid conditions — the swelling of the polymer network accommodates the excess water.

Under lower humidity, the film releases water and returns to its original size. This reversible behavior helps the film maintain integrity and flexibility, supporting wear comfort across humidity levels.

"...[T]he thickness of the coating film changes in response to the humidity environment, absorbing and desorbing excess moisture," Kawamoto reiterated. "This effect has been shown in consumer surveys to reduce stickiness in high-humidity environments and to prevent drying in low humidity environments." 

To assess the adaptive mechanism, Kao performed gravimetric analysis and film thickness measurements under changing humidity conditions. Testing included cycling relative humidity between 20% and 88%. 

Results showed the adaptive film undergoes reversible dimensional changes: swelling at high humidity (88% RH) with moisture uptake approximately twice that of a control formulation, and restoration to its original dimensions at 20% RH as water is released. This process confirms the polymer network’s role as a reversible moisture buffer that does not compromise film integrity.

Interestingly, Kao Corp.'s sunscreen was not originally developed to be climate-adaptive — it was a serendipitous discovery. "Initially, the goal was to develop a formulation with a light, 'airy' feel," wrote Kawamoto.

"When we were sweating in a hot and humid environment after applying the prototype, we noticed a difference in the appearance and feel of perspiration compared to the existing water-based formula," Kawamoto shared.

Additional Polymer Benefits

Kawamoto emphasized the polymer chosen also had to be safe for leave-on formulations and it could not fall under microplastic regulations. Further, it had to be proven safe for skin, as testing of the final formula confirmed. 

"While it is unclear whether components derived from agar are responsible, we ... conducted RIHPTs (repeated insult human patch tests) and non-comedogenic tests to confirm that the formulation is not highly irritating to the skin," Kawamoto noted.

Impact on Consumer Compliance?

To this point, it seems the sunscreen formula met the required physical requirements. So how did it impact user compliance?

According to Kawamoto, users found that "'skin comfort lasted throughout the day' and the 'light, airy feel' led consumers to 'want to apply a generous amount' of sunscreen." Furthermore, the "'long-lasting skin comfort' and 'airy, lightweight feel' have been shown to lead consumers to 'want to apply sunscreen liberally.'"  

Indeed, per Kawamoto, an internal study found that the final Bioré UV Aqua Rich Airy Hold Cream formula increased the amount of sunscreen applied by users up to 1.5 times more than existing water-based sunscreens. 

"Throughout the day, the UV protective film repeatedly absorbs and exhales humidity," explained Kawamoto. "Consumer surveys have shown that this makes it less likely to feel sticky in hot and humid environments and less likely to feel dry in dry environments. 

"We do not have specific data on differences in re-application frequency," he continued, "but we know that the airy UV [product] has a shorter purchase cycle compared to existing water-based formulations. Based on this result, we believe usage volume and the number of reapplication instances have increased."  

According to Kawamoto, the increased amount of sunscreen applied in actual use also increased the effectiveness of UV protection, leading to the feeling of no sunburn. "These effects have been shown to lead to a high repetition rate, with approximately 90% of respondents to a buyer survey indicating that they would like to purchase this product again."

Future Endeavors and Climate-Responsive Beauty

So, what other aspects of formulas could become a focus for climate-adaptive beauty? "Kao has already developed technologies to suppress the adhesion of air pollutants and block near-infrared rays to reduce the uncomfortable heat sensation," highlighted Kawamoto. 

"Beyond that, we believe the essential formulation elements for achieving global adoption by many users are the ability to protect skin from UV rays even in increasingly harsh climates — marked by dryness, dirt, heat and sweat — while simultaneously delivering a pleasant feel that encourages continued use." 

Conclusion

Kao’s adaptive sunscreen technology illustrates an innovative use of humidity-responsive polymers and agar hydrogel to address the challenges of climate-adaptive beauty. By flexibly adjusting to shifts in moisture, this approach offers practical protection and comfort for skin in changing environments.