Body odor affects a broad range of people and has created an ever-expanding market for body odor control and neutralization. There have been more than 56,000 product launches in the past three years alone that fall into the soap and bath category, which includes shower gels, body wash and bar soaps. Of these, 35% have odor claims and/or include relevant ingredients such as triclosan, menthol, linalool and triclocarban. Europe is the leading region, accounting for 55% of these launches.¹ The increasing desire for odor control products, combined with a greater understanding of the causes behind body odor, creates a market seeking new solutions, including finding new uses for known chemistries as an alternate to traditional body odor actives.


Body odor develops for a variety of reasons. Factors such as excessive sweating, obesity, medical conditions or high intake of spicy foods can all contribute to an individual experiencing a unique, and many times unwanted, body aroma. The main culprit of what is typically considered as an offensive body odor comes from the breakdown of our apocrine sweat by microorganisms.


Human skin has two main types of sweat glands, eccrine glands and apocrine glands, which produce two very different types of sweat, both sterile and odorless. Eccrine glands occur over most of the body and open directly onto the surface of the skin. The sweat produced from eccrine glands is made mostly of water and is high in salt content. Apocrine glands, however, are concentrated in areas abundant in hair follicles, such as armpits and the groin area. Apocrine sweat contains a high content of proteins and lipids that bacteria feed on. It is the breakdown of this sweat by particular microorganisms present on the skin’s surface that leads to body odor.


The link between body odor and microorganisms on the skin has long been known. But with the advent of high-throughput technologies, it is possible to correlate specific microbiota, abundancies and odorous volatile compounds with each other.² Some organisms implicated in body odor include Corynebacterium minutissimum, Corynebacterium xerosis, Micrococcus luteus, Staphylococcus epidermidis, Staphylococcus haemolyticus and Propionibacterium.^2-4 These specific bacteria secrete enzymes extracellularly, which react with lipids present in human sweat and break them down to produce odorous byproducts.


Of the compounds released by bacteria, body odor is typically attributed to a handful of small-molecule organic acids and sulfur-containing compounds. Propionibacterium live in the ducts of the sebaceous glands of adult and adolescent humans and break down amino acids into propionic acid (propanoic acid). Structurally similar to acetic acid, which gives vinegar its sour taste and pungent smell, propionic acid has been identified as producing a strong vinegar-like smell.⁵ Isovaleric acid (3-methyl butanoic acid) is another source of body odor produced by staphylococcus bacteria, in which is often singled out for giving a number of strong cheese types their distinctive—and often pungent—smell.⁵ THMA (trans-3-methyl-2-hexenoic acid) has been attributed to corynebacterium activity, and is associated with the distinct cumin-like aroma of axillary odor.⁶ Small-molecule sulfur compounds such as 3-methyl-3-sulfanylhexan-1-ol are associated with a variety of axilla bacteria and produce a strong unpleasant smell often associated with body odor.


Solutions

There are many possible treatments for body odor. The most common is the use of over-the-counter antiperspirants to prevent the production of sweat in the first place. When traditional antiperspirants do not produce the desired results, some people may look to more invasive remedies such as Botox, laser treatments and surgery. Another approach beyond reducing sweat is through preventing organisms implicated in body odor from initially growing on the skin. With a greater understanding of the microorganisms involved in body odor as well as increased scrutiny on traditional actives in body odor control, a second look at established antimicrobial chemistries such as zinc pyrithione is warranted.  


Studies have shown that zinc pyrithione is extremely effective in eliminating the fungi Malassezia sp., which is directly linked to the scalp condition dandruff. An important characteristic of this molecule is that it is efficacious against numerous other organisms beyond Malassezia, including the various bacteria species associated with producing odor on the skin. Here we demonstrate the ability of zinc pyrithione to control the growth of these odor-causing organisms and thus provide an alternative chemistry for odor control.


Zinc pyrithione acts as an antimicrobial through disruption of the proton gradient across the cell membrane. By moving freely in and out of the cell membrane and taking ions with it, zinc pyrithione carries potassium and magnesium out of the microbe until the microbe is completely depleted of these nutrients and is unable to function normally and dies. This mode of action does not interfere with cell wall enzymes, which means the organism does not mutate and become resistant to the continued use of the antimicrobial. Additionally, we know that zinc pyrithione has additional properties that play into its efficacy. This molecule is an efficient chelator of iron and has been shown to deplete the cells of this essential nutrient.


Efficacy Data

Minimum inhibitory concentration (MIC) is an in vitro test that determines the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation. A MIC value is generally regarded as the most basic laboratory measurement of the activity of an antimicrobial agent against an organism and is typically used as an initial screening for determining efficacy.⁷


MIC studies were performed to determine the efficacy of zinc pyrithione on numerous organisms that play a part in odor formation. Results show activity at low ppm values, making zinc pyrithione a viable candidate for body odor control.


Zinc Pyrithione (ppm)
S. epidermidis  15.6

C. minutissimum 7.8

S. haemolyticus 31.3

C. xerosis 3.9

M. luteus 15.6


In vitro antimicrobial tests were performed on a pig skin substrate following a proprietary method in order to determine the efficacy of zinc pyrithione for body odor control in final formulated products. Treated pig skin was inoculated with a mixed culture containing C. minutissimum, C. xerosis, M. luteus, S. epidermidis and S. haemolyticus, and then evaluated over time for bacterial growth.


The first study compared zinc pyrithione to triclosan and triclocarban, both commonly used actives for odor control. The study demonstrates that zinc pyrithione provides comparable—if not better—long-term efficacy than traditional actives. Results of the standalone actives after a 6-hour pig skin study show zinc pyrithione is effective in the long term decrease in the number of odor-causing organisms.


In a second study on pig skin, we looked at zinc pyrithione dispersions in a bar soap formulation showing that after five hours, both the traditional fine particle dispersion and a palm oil-coated zinc pyrithione dispersion had a long term bacteriostatic effect on the odor-causing organisms.


Lastly, zinc pyrithione dispersions were formulated into a body wash and then tested on pig skin substrate again, demonstrating the effectiveness of both a traditional fine particle dispersion and a palm oil-coated zinc pyrithione dispersion for long-term bacteriostatic effect.


The market for body odor control and neutralization is expanding with ongoing research into how odor control on the body could be targeted differently. This research includes identifying various chemistries that can be active for this target as well as the mode of action for chemistries. Zinc pyrithione is a chemistry that has been identified in playing a role in controlling the types of bacteria on the skin that can lead to body odor.


Regulatory Note

Zinc pyrithione is a listed preservative in EU Cosmetic Reg Annex V and allowed in rinse-off products only. For products other than those for hair, it is permitted up to 0.5%. Lonza recommends an upper use level of 0.25% zinc pyrithione for whole body rinse-off products.


A finished formulation sold in the US that contains Zinc Omadine 48% FPS or Zinc Omadine Enhanced CP Dispersion cannot include any antimicrobial claims or reference the biocidal nature of the material against any particular organism. Zinc Omadine 48% FPS or Zinc Omadine Enhanced CP Dispersion can be used in rinse-off deodorant applications but cannot be used as an active ingredient to make antimicrobial claims, including when used in cosmetic grade deodorant or antibacterial handwash/soap applications. FDA has classified deodorants as cosmetics and zinc omadine is not listed in FDA’s Tentative Monograph: OTC Healthcare Antiseptic Drug Products (which supports antimicrobial hand washes and soaps).


Proper use of this information is the sole responsibility of the recipient.


References

1. Mintel August 2017 GNPD database
2. Troccaz, M., et. al. Mapping axillary microbiota responsible for body odors using a culture-independent approach. Microbiome, 2015, 3(3).   doi:10.1186/s40168-014-0064-3.
3. Barzantny H., et al. Molecular basis of human body odour formation: insights deduced from cornebacterial genome sequences. International   Journal of Cosmetic Science, 2012, 34, 2-11
4. Leyden, J. et. al. The Microbiology of the Human Axilla and Its Relationship to Axillary Odor. The Journal of Investigative Dermatology, 1981, 77(5), 413-416.
5. http://medicalnewstoday.com/articles/173478.php
6. Natsch, A., et. al. A specific bacterial aminoacylase cleaves odorant  precursors secreted in the human axilla. Journal of Biological Chemistry, 2003,   278(8), 5718-27.
7. Turnidge JD, Ferraro MJ, Jorgensen JH (2003) Susceptibility Test  Methods: General Considerations. In PR Murray, EJ Baron, JH Jorgensen, MA Pfaller, RH Yolken. Manual of Clinical Microbiology. 8th Ed. Washington. American Society of Clinical Microbiology. p 1103 ISBN 1-55581-255-4