by Phil Klepak and Barbara Schmidt
published in the CosmetiSCOPE April 2021 issue New York Society of Cosmetic Chemists
There has been a growing trend over the last several years of using natural products with medicinal activities, particularly in overseas markets. Plant extracts have been identified for the treatment of acne, psoriasis, and dandruff. At present, the FDA has only classified a few botanicals as GRASE for a specific OTC drug use. This article addresses whether some plants contain sufficient bioactive phytochemicals that could function as “natural” antiperspirants when applied from a topical formulation. According to the U.S. FD&C Act, the FDA classifies antiperspirants (reduce underarm perspiration) as OTC drugs, while deodorants are classified as cosmetics. Globally, most countries classify antiperspirants as cosmetics, including those products with duration of effect claims. This is true in the European Union, Australia, New Zealand, South Africa, and Latin America. In Canada, classification depends on the claims, and in Japan they are “quasi-drugs” (the difference vs. a cosmetic is somewhat ambiguous). Only the U.S. and UK have quantitative standards for antiperspirant performance. Therefore, if your product reduces perspiration statistically better than a control, you can label your product an antiperspirant
Ingredients from Nature
Natural products have a range of bioactivities to reduce sweating including astringency to contract skin pores, absorbency, decreased sweat stimulation via the parasympathetic nervous system, and protein
aggregation forming sweat pore plugs. Plants have been used for centuries to reduce excessive sweating, but in Traditional Chinese Medicine and Ayurveda, most were taken orally for fever diseases like malaria or perceived systemic health issues. Topical sweat reducers for everyday sweating are uncommon in ethnobotanical literature and even fewer have been tested clinically in controlled trials.
In Traditional Chinese Medicine, Chinese sumac galls, turmeric, schisandra, ephedra root, mulberry leaf, and Amur cork tree bark are applied topically to reduce excessive sweating. All of these herbs can be mixed with minerals or starches to help absorb sweat. Chinese sumac galls contain gallotannins with astringent and protein cross-linking properties that may reduce sweat. The other herbs contain primarily polyphenols (turmeric, schisandra) and/or alkaloids (Amur cork tree bark, mulberry leaf, and ephedra) with little scientific validation aside from polyphenol astringency. Mulberry leaves and ash tree bark (Qin Pi) were tested in a clinical trial for foot sweating. When used as a 15-minute foot soak, they reduced foot sweating by an average of 15% in a pilot study with 20 healthy volunteers. 1 Both herbs have antibacterial properties, which could help reduce foot odor.
A combination of five Ayurvedic herbs (Himalayan cedar, nut grass, jasmine, black turmeric, and vetiver) traditionally used as a topical remedy for foot odor and excessive sweating were tested in a controlled clinical trial. 2 After 15 days, there was a reduction in foot odor, sweating, and itching. The herbs contain a variety of phytochemicals such as essential oils rich in antimicrobial terpenes that may be responsible for the positive results.
In North America, the Navajos used rough cocklebur liniment for underarm sweating. In Europe, traditional antiperspirant formulations include common yarrow (Achillea millefolium), soapwort (Saponaria officinalis), and elderberry (Sambucus nigra) flowers, sage (Salvia officinalis and S. libanotica), horsetail (Equisetum arvense), rockrose (Cistus ladanifer), and Milkvetch (Astragalus spp.). However, there are no published clinical studies to validate any of these herbs as effective antiperspirants.
Research and Development Challenges of a Natural Antiperspirant
Clinical efficacy testing of the final antiperspirant formulation is necessary to support the specific claim of “reduces underarm sweating”. This means that the natural extract should be tested at the level required to demonstrate the intended claim. The performance target can be either a statistically significant sweat reduction compared to a placebo or to meet or exceed the minimum quantitative FDA standard using their statistical standard.
Ingredient screening tests could be helpful prior to conducting an underarm wetness clinical study, namely measuring the electrical conductance/impedance of the skin, TEWL from the skin by detecting changes in relative humidity, or protein aggregation in a microfluidic test system. Some challenges should be recognized and factored into R&D plans. First, our evidence from pilot studies suggests that natural extracts may not be as effective as aluminum-based salts. Since natural extracts are a mixture of compounds, there can be substantial variation depending on the source. A standardized phytochemical profile may be necessary for quality control. Furthermore, some natural extracts can be difficult to work with. For example, are they prone to contamination or do they present preservation concerns? Formulations containing natural extracts could have a shorter shelf life due to degradation of the active component over time. It may be appropriate to follow the stability of several marker compounds.
Botanical ingredients are available as a liquid extract mixed in solvents like glycerin and glycols or in powder form with or without excipients. Many phytochemicals are easily oxidized, especially at room temperature in the presence of solvents including water and alcohols. We have observed considerable, rapid degradation of phytochemicals in plant extracts when stored in a liquid or cream base. In contrast, we found dry extracts from the same plants retained their phytochemical integrity and clinical antiperspirant efficacy for 18-24 months at room temperature. Also, we have observed a loss of phytochemicals when mixed with certain “inert” excipients, possibly due to irreversible adsorption. One significant hurdle of using dry extracts is difficult dissolution. Experimental trial and error experiments are required to find the optimal solvents, heat, and agitation for dissolution.
Many cosmetic chemists are aware of the unique challenge posed by natural products in cosmetic
formulations. High batch temperatures must be avoided to reduce phytochemical degradation. When
using waxes that require high melting temperatures, the extracts could be incorporated at the end of
the batch, after the temperature has dropped. Even after extracts or pure phytochemicals are fully
dissolved and incorporated into the formula, they can precipitate once the batch cools or after a longer
period of time. They can cause an emulsion to split over time or lose viscosity. They can react with
packaging and frequently change the formula color from light to brown. A rigorous experimental process
is usually required to find a formula that optimizes both phytochemical and formulation stability.
Specific guidelines and protocols for the efficacy assessment of underarm antiperspirants are well
documented in a variety of published sources such as the FDA/Federal Register (2003), EEMCO (2003),
and Clearcast (2019).
These gravimetric protocols quantify the amount of eccrine sweat produced in the underarms during
specific time intervals and under controlled conditions. More sophisticated testing options are also
possible to support claims such as longer duration of efficacy, physical activity resistance, psychological
stress protection, extreme heat resistance, night sweats, etc.
Based on our knowledge and testing of natural extracts, they exhibit less efficacy than aluminumbased salts, so it is important to ensure that their wetness reduction performance can be measured with
statistical confidence. Also, assessing small amounts of sweat at weak excretion rates is difficult, and
requires experimental skill. Therefore, the following is recommended to design and conduct a successful
clinical test of natural extracts:
- Baseline sweating values in both armpits should be similar and not skewed. A spread between the lowest and highest sweaters of at least 600 mg is recommended with a minimum of 100 mg sweat per armpit.
- Pro-perspirer panelists (i.e., sweating more after product treatment) should not be enrolled.
- Mixed gender test panels are not recommended to avoid any questionable results due to surface area and sweat volume differences. Female panelists are generally used.
Typical sweat reduction clinical trial results for a formulation containing a combination of two plant extracts rich in polyphenols and diterpenes were as follows: 24% at the original concentration of actives, 29% at twice the concentration of actives, and 20% at the original concentration of actives then aged for 18 months.
Marketing Justification
The global underarm products market is healthy with growth fueled by the youth population. Lifestyle changes which include a focus on hygiene, daily grooming routines, disposable income leading to discretionary toiletry products becoming daily necessities, and product format and ingredient innovations are key factors currently driving the market.
A concurrent global trend in the cosmetics market in general is the rising consumer awareness of natural ingredients with therapeutic or biological effects. Despite significant evidence to the contrary, the safety of aluminum salts is under continued scrutiny even though the links to breast cancer, Alzheimer’s disease, and
dermal absorption are not generally accepted in the scientific and medical communities, and some studies are even discredited. This continued negative perception of aluminum-based antiperspirants is contributing to a growing consumer demand for natural antiperspirants specifically for sticks, creams, and emulsions.
Given the consumer demand for natural antiperspirants, and ethnobotanical knowledge of several herbs used as topical antiperspirants, more resources should be devoted to identifying potential antiperspirant ingredients from natural sources and verifying their clinical efficacy. Once potential candidates have been identified, challenges such as reliable ingredient sourcing, formulation, and stability can be overcome with dedicated R&D investment.
References
- P.C. Leung, et al. Evaluation of the topical antiperspirant effects of a simple herbal formula, Clin.
Med. Invest., 2(1): 1–3 (2016). - A.V. Kamble and M.R. Joshi, A clinical study to evaluate the efficacy of Ayurvedic/herbal
deodorant on sole, WJPR, 6(13): 862–872 (2017).
About the Authors
Phil Klepak retired in 2018 after 31 years of direct experience in all aspects of antiperspirant and deodorant technology with Reheis/SummitReheis/Elementis as
Global Director of Technical Services. This included knowledge of chemistry,
formulations, process troubleshooting, clinical testing protocols, etc. He also taught
the SCC continuing education course on antiperspirants and deodorants for many
years.
Barbara Schmidt has a Ph.D. from the University of Illinois, Urbana-Champaign
where she studied phytochemistry. She specializes in botanical raw materials for
the personal care and dietary supplement industries. She authored an
enthnobotany textbook in 2017 and is currently teaching phytochemistry for the
Rutgers University Global Institute for BioExploration (GIBEX).
more about antiperspirants in the article “Natural antiperspirants: dream or reality?“