Evaluation of C13-15 Alkane as a Replacement for D5 in Stick and Aerosol Antiperspirants

Introduction

Over 35,000 personal care products were launched containing cyclomethicones or cyclopentasiloxane (D5) between 2014 and 2019 according to Mintel GNPD. D5 is widely used to promote even coverage, spreadability, and to provide a light and dry afterfeel in a wide range of applications including antiperspirants. According to Mintel, 65% of all antiperspirants contained D5 between 2016-2019. However, more and more consumers are demanding “silicone-free” products and in recent months, ECHA has listed cyclomethicone as a “Substance of Very High Concern.” As of January 2020, it is now restricted to levels of no more than 0.1% in wash off products in the EU, and similar bans for leave-on applications are under consideration as early as 2021. Today, formulators are actively searching for alternatives to meet regulatory and consumer needs despite the particular challenges of cyclomethicone replacement in this category.

C13-15 Alkane, marketed by Aprinnova LLC under the trade name of Neossance™ Hemisqualane, has been shown to meet formulator demands for cyclomethicone replacement in a wide variety of skin, color, and applications [1]. Hemisqualane is sustainably sourced from Brazilian sugar cane and is 100% naturally derived according to ISO standard 16128. Throughout this technical paper, we will demonstrate how to formulate D5-free antiperspirants using Hemisqualane that, via expert panel sensory and consumer studies, are judged to be equivalent to or superior to D5 containing formulas.

Antiperspirant Stick Formulation

Formulations:

There is no drop-in replacement for D5 on the market today. However, across applications we have proven successful replacements with Hemisqualane using a two-pronged approach: ingredient substitution and formulation adjustment. In antiperspirant sticks, we have identified a few ways to close the performance gap, and it can be achieved by 1) replacing D5 by volume, not by weight as density of Hemisqualane is slightly lower, 2) adding oil absorbers such as silica, starch or talc to reduce shine, and 3) adding high melting point waxes to improve stick integrity. Formulations used in sensory and consumer studies reported in this document for the stick format are listed in Table 1.

Table 1. Formulations used in antiperspirant stick studies

Expert Sensory Evaluation of Antiperspirant Stick

Methodology:

An expert panel evaluation with 12 panelists was conducted comparing formulations with Hemisqualane and D5 using the Skinfeel Descriptive Analysis Method based on ASTM MNL13. For skin preparation, all panelists were directed to use a non-abrasive soap at least 10 minutes prior to the start of the study. A 6 in. x 2 in. skin scribe was used to make a rectangle in the crook of each arm insuring that the fold of the arm bisects the rectangle. The rectangle was divided into 3 sections, one on each side of the fold, leaving a 2 in. square around the fold. Sample presentation was rotated among panelists, with each sample evaluated twice. Attributes were assessed using a 0–100 point intensity scale where 0 is none and 100 is very strong. Statistical analyses (ANOVA) were used to highlight significant differences among samples for each attribute.

Results:

During application, there are no significant differences for cooling and occlusion (Graph 1). In the immediate afterfeel, the Hemisqualane prototype has a higher gloss on skin, feels more moist and more slippery than the D5 counterpart. Stickiness in the crease of the arm for Hemisqualane is slightly lower. At 15 minutes after application, the Hemisqualane prototype has a higher thickness of residue and gloss on skin, and is directionally more slippery but feels less taut. Rub-off whitening on fabric is higher in the D5 prototype. Overall, differences between the two antiperspirant sticks are small and attribute intensities are low.  Typically differences of <10 intensity points are not expected to be perceivable by consumers. The concept of statistical difference in these expert panel studies are that these trained evaluators have, at a 95% confidence level, consistently judged an attribute different, albeit how small the difference between the values. Scoring of the key attributes detected in the Hemisqualane and D5 formulas are presented in spider charts in Graph 2.

Graph 1. Comparing D5 and Hemisqualane formulas during application

Graph 2. Immediate (left) and 15-minute (right) afterfeel comparing D5 and Hemisqualane formulas

Consumer Perception Studies of Hemisqualane Antiperspirant Sticks

Two consumer perception studies were carried out to determine the consumer’s perception of an antiperspirant stick with Hemisqualane compared to an antiperspirant stick with D5 or compared to their current at-home antiperspirant. The methodology for the two studies was the same in principle.

Methodology:

Both consumer studies were carried out in the United Kingdom and consisted of at least 50 individuals. The consumers were provided directions on and frequency of use for the products. After completion, the participants were given a specifically designed questionnaire and asked to answer each question on a scale from 1 to 9 with 1 being “strongly disagree” and 9 being “strongly agree.” The responses were analyzed for overall consumer acceptance (percentage of responses 6 through 9). The Hemisqualane vs D5 study also included statistical analysis of each question between the two formulations.

Hemisqualane vs D5 Antiperspirant Stick:

Participants: 50

Samples: Hemisqualane Antiperspirant, D5 Antiperspirant

Use & Frequency: Use each product once a day for 3 days

Results:

Consumers confirm sensory equivalence of the Hemisqualane antiperspirant stick with the D5 stick for  sensorial benefits typically associated with D5, such as dry feel, spreadability, and sensorial. No statistically significant differences were observed between the two formulations for each question. Consumer satisfaction for each question is shown in Graph 3 with Hemisqualane formulation in green and the D5 formulation in blue. Each question is listed on the y-axis and grouped by benefit. Overall consumer satisfaction as a percentage of responses 6 thru 9 is on the x-axis. All of the statements in Graph 3 received sufficient consumer satisfaction scores (>=66%) to be used for claim substantiation.

Graph 3. Consumer satisfaction for each question presented

Hemisqualane Antiperspirant Stick Compared to Current Brand

Methodology:

Participants: 60

Samples: Hemisqualane Antiperspirant

Use & Frequency: Use each product once a day for 3 days

Results:

The Hemisqualane Antiperspirant stick is well-accepted by consumers and performs the same as or better than their current at-home antiperspirant. Consumer satisfaction for each attribute is listed in Table 2 and all attributes received high enough scores to be used for claim substantiation

Table 2. Consumer satisfaction for each attribute

Additionally, 80% of consumers agreed they “would switch to the Hemisqualane antiperspirant if they knew their current product contained silicones”.

Some selected consumer comments for the Hemisqualane prototype include:

“… dries more quickly, left no marks on clothes, and kept me feeling fresh”

“Product glides on well and dries quickly. I enjoyed using it.”

“I like this product, it goes on smoothly and kept me dry and fresh.”

“A great feeling antiperspirant that I would switch to from my regular product.”

“I liked the fact that it’s silicone free and does not feel at all when applied. It totally feels normal.”

Antiperspirant Aerosol Formulation

Formulations:

A similar approach is applied in replacing D5 in aerosol formulations. As shown in Table 3, the Hemisqualane prototype is made by replacing D5 with Hemisqualane based on volume alone.  All other ingredients were adjusted accordingly prior to adding propellant.

Table 3. Formulations used in aerosol expert panel sensory study

Expert Sensory Evaluation of Antiperspirant Aerosol

Methodology:

An expert panel evaluation of 9 panelists was conducted comparing formulations with Hemisqualane and D5 using the Skinfeel Descriptive Analysis Method based on ASTM MNL13. For skin preparation, all panelists were directed to use a non-abrasive soap at least 10 minutes prior to the start of the study. A 8 in. x 2 in. skin scribe was used to make a rectangle in the crook of each arm insuring that the fold of the arm bisects the rectangle. The rectangle was divided into 4 sections to allow for a fresh area for each evaluation time point (immediate, 5- and 15-minute; stickiness at arm fold), leaving a 2 in. square around the fold. No test sites were re-used during a session, and one product was evaluated on each arm. Sample presentation was rotated among panelists, with each sample evaluated twice. For product appearance and product pick-up, product was sprayed into a plastic bottle and slightly shaken prior to evaluations. Attributes were assessed using a 0 – 100 point intensity scale where 0 is none and 100 being is very strong. Statistical analyses (ANOVA) were used to highlight significant differences among samples for each attribute.

Results:

In product pick-up and appearance, the Hemisqualane sample pools more quickly which indicates a lower integrity of shape. There are no significant differences between samples when manipulated (during pick-up). During application, the Hemisqualane prototype is cooler with stronger spray pressure (Graph 4). Immediately after application, the Hemisqualane prototype has a slightly higher stickiness in the crease of the arms, and statistical differences are detected in skin gloss, wetness, stickiness and occlusion. In terms of residue, the aerosols do not leave much tactile residue on skin, and no statistically significant difference is detected immediately after application. The waxy, greasy and plastic character of the residue may not be relevant since attribute intensities are very low and close to baseline (Graph 5). At 5 and 15 minutes after application, there continues to be small statistical differences between samples for skin gloss, occlusion, wetness and stickiness, with the Hemisqualane sample giving a slightly higher intensity than D5. On the other hand, the D5 sample leaves a higher white residue on black fabric indicating rub-off whitening. While the skinfeel sensations may not be relevant since ranges are small and attribute intensities are low or close to baseline, differences in rub-off whitening may be significant (Graph 6).

All in all, differences detected by the expert panel during application and in afterfeel, albeit statistically significant, are well below the threshold of possible consumer perceivable differences. Hence these differences are very likely not to be noticed by consumers. On the other hand, the higher white residue left on dark fabric by the D5 prototype may be detected by consumers as it is visual.

Graph 4. Product appearance during application

Graph 5. Immediate afterfeel

Graph 6. Residue type at 5 and 15 minutes

Consumer Perception Studies of Hemisqualane Aerosol Antiperspirant

A consumer perception study was carried out to determine the consumer’s perception of an aerosol antiperspirant with Hemisqualane compared to an aerosol antiperspirant with D5.

Methodology:

The consumer study was carried out in the United Kingdom and consisted of 58 individuals. The consumers were provided directions on and frequency of use for the products. After completion, the participants were given a specifically designed questionnaire and asked to answer each question on a scale from 1 to 9 with 1 being “strongly disagree” and 9 being “strongly agree.” The responses were analyzed for overall consumer acceptance (percentage of responses 6 through 9). The Hemisqualane vs D5 study also included statistical analysis of each question between the two formulations.

Hemisqualane Aerosol Antiperspirant vs D5 Aerosol Antiperspirant:

Participants: 58

Samples: Hemisqualane Aerosol Antiperspirant, D5 Aerosol Antiperspirant

Use & Frequency: Use each product once a day for 3 days

Results:

Consumers confirm sensory equivalence of the Hemisqualane aerosol antiperspirant with the D5 aerosol for sensorial benefits typically associated with D5. No statistically significant differences were observed between the two formulations for each question. Consumer satisfaction for each question is shown in Graph 7 with Hemisqualane formulation in green and the D5 formulation in blue. Each question is listed on the y-axis and grouped by benefit. Overall consumer satisfaction as a percentage of responses 6 thru 9 is on the x-axis. All of the statements in Graph 7 received sufficient consumer satisfaction scores (>=66%) to be used for claim substantiation.

Graph 7. Consumer satisfaction for each question presented

Hemisqualane Aerosol Antiperspirant Compared to Current Brand Methodology:

Participants: 58

Samples: Hemisqualane Aerosol Antiperspirant

Use & Frequency: Use product once a day for 3 days

Results:

The Hemisqualane Aerosol Antiperspirant is well-accepted by consumers and performs the same as or better than their current at-home antiperspirant. Consumer satisfaction for each attribute is listed in Table 4 and all attributes received sufficient scores to be used for claim substantiation.

Table 4. Consumer satisfaction for each attribute

Additionally, 70% of consumers agreed they “would switch to the Hemisqualane antiperspirant if they knew their current product contained silicones.”

Conclusion

Expert panel studies comparing antiperspirants in both stick and aerosol formats with Hemisqualane and D5 demonstrate equivalence over most attributes and superior performance in immediate and short-term afterfeel. More importantly, the equivalent performance in antiperspirant sticks and aerosols are verified by two types of consumer studies: direct comparison of Hemisqualane and D5 prototype as well as comparison to the participant’s current product.

These studies demonstrate Hemisqualane is a high performance D5 alternative that offers an excellent sensorial experience and is proven to deliver high consumer satisfaction in antiperspirant applications.

References:

[1] Aprinnova. The Future of D5 Replacement. Poster session presented at the 73rd Annual Scientific Meeting & Technology Showcase; 2019 December 17-19; New York, NY