I have decided to dive into Russian literature on the history of phytoncides, as little is found in English on the subject. The relevance of phytoncides to forest therapy and Shinrin Yoku is significant, especially given that the term “Shinrin Yoku” was coined in Japan. Russian research, particularly the work of Boris Petrovich Tokin, sheds light on the development of phytoncide science and its applications in health and wellness. I also invite to our new continuous professional  development program for Forest Therapy/Forest Bathing/Shinrin-Yoku Guides on phytoncides.

The Origins of Phytoncide Therapy

Boris Petrovich Tokin was a key figure in Soviet biological thought in the mid-20th century. His discovery of the fungicidal properties of volatile emissions from garlic and onions in 1929 led to decades of research on the bactericidal activity of essential oils under the framework of phytoncide studies. Tokin’s work provided foundational insights into the antimicrobial and antifungal properties of plant emissions, shaping the development of what would later be recognized as phytoncide therapy.

Tokin’s pivotal experiments involved using crushed onion tissues to investigate mitogenetic radiation, a concept introduced by A. G. Gurvich. His observations of yeast cell mortality in the presence of onion extracts initially puzzled him, but by 1932, he recognized the fungicidal and bactericidal nature of plant volatile compounds. A defining moment occurred during a visit to Tashkent and Samarkand, where he speculated that the strong spices used in street food might combat harmful bacteria—a hypothesis that led him to systematically study plant-derived bactericides.

Tokin first introduced the term “phytoncides” in a 1942 publication, “Plant-Derived Bactericides (Phytoncides).” This term, derived from the Greek phyton (plant) and Latin caedo (to kill), described plant-based compounds capable of destroying bacteria, fungi, and other harmful microorganisms. His discoveries gained traction during World War II when bacterial infections posed a significant threat, and natural antimicrobial solutions were urgently needed.

From 1930 to 1934, researchers led by Tokin, including surgeon A. G. Filatova and microbiologist A. Tebyakina, conducted studies demonstrating the potent antibacterial effects of plant essential oil vapors on pathogens such as Escherichia coli, Staphylococcus, Streptococcus, and Salmonella typhi. By the mid-20th century, the Kiev Microbiology Institute, led by V. G. Drobotko, became the epicenter of Soviet phytoncide research.

Mechanism of Action of Phytoncides on Protozoa

A. Kovalenok’s study, presented by academician L. A. Orbeli on November 18, 1942, expanded on Tokin’s research, exploring the effects of phytoncides on protozoa. Kovalenok and Filatova found that volatile phytoncides from fresh onion (Allium cepa), garlic (Allium sativum), and other plants exhibited powerful bactericidal properties. Their research demonstrated that a mere 3-5 minute exposure could inhibit the growth or completely kill certain fungi and bacteria strains.

Their study also revealed that phytoncides were lethal to unicellular organisms, including free-living and parasitic protozoa. They conducted experiments on various species, including ciliates, flagellates, and Opalina ranarum (Ehrbg.), a ciliate living in the intestines of frogs (Rana arvalis L.). The results showed varying effects on different protozoa, though all eventually succumbed to phytoncide exposure.

For instance, Paramaecium caudatum Ehrbg. (is a species of unicellular ciliate protozoa belonging to the genus Paramecium. It is one of the most well-studied microorganisms and is commonly found in freshwater environments such as ponds, lakes, and slow-moving streams) initially exhibited hyperactive movement upon exposure, doubling or tripling its speed before slowing down and dying within three to four minutes. The morphological changes included an elongated anterior end, rounded posterior, and increased cytoplasmic granulation. Shortly after ceasing movement, the formation of small transparent vesicles on the cell surface was observed. The exact nature of these vesicles remains unclear, but theories suggest a reaction between phytoncide vapors and the cell membrane or the expulsion of cytoplasmic content.

Further experiments indicated that a mere 30-second exposure to onion-derived phytoncides was sufficient to cause irreversible changes in Paramaecium caudatum, leading to death within minutes. The study also examined Stentor coeruleus Ehrbg., which reacted with body contractions and viscosity changes before complete breakdown. Stylonychia mytilus Ehrbg. exhibited rapid movement, followed by cell lysis beginning at the peristome region. Other species, such as Loxodes rostrum O.F. Mull., underwent lysis within 10-15 seconds of phytoncide exposure.

Kovalenok extended his research to include different plant sources, such as Allium schoenoprasum L. (chives) and Paeonia anomala (peony roots). While the general impact of phytoncides remained consistent, the exposure duration required to kill protozoa varied: onion phytoncides acted within 2-3 minutes, chives within 3-5 minutes, and peony roots within 7-9 minutes. These findings suggested that different plant-derived phytoncides had distinct potencies, an insight relevant for applications in controlling pathogenic protozoa.

The study also raised questions about the physiological mechanisms behind the protozoan response. Researchers speculated that phytoncides might alter cell membrane permeability, leading to osmotic imbalance and eventual cell death. Alternatively, the compounds might directly interfere with essential cellular processes, triggering apoptosis-like reactions in unicellular organisms.

The term “phytoncides” was officially introduced into scientific literature only in 1942, with the publication of Plant-Derived Bactericides (Phytoncides) / «Бактерициды растительного происхождения (Фитонциды)».

From the 1950s onward, the Kyiv School of Microbiologists, under the leadership of V. G. Drobotko at the Institute of Microbiology and Virology of the Ukrainian Academy of Sciences, became the primary center for phytoncide research. Tokin repeatedly emphasized the crucial role of this institute in advancing the field, describing it as the leading research hub on the subject within the USSR. Among the Ukrainian scientists contributing to this field, N. G. Kholodny was particularly recognized by Tokin for his significant influence on the development of phytoncide studies .

Over the following decades, Tokin authored research papers and additional books on phytoncides, collectively published in Russian, German,  Chinese, Japanese, and Bulgarian. His seminal work, Plant-Derived Bactericides (Phytoncides) / «Бактерициды растительного происхождения (Фитонциды)», laid the foundation for phytoncide therapy (фитонцидотерапия), which, at the time, was understood as the use of volatile organic compounds , released by plants, to combat bacteria and fungi.

Fast-forwarding to 1980, Tokin co-authored The Amazing Power of Plants – Phytoncides / «Удивительная сила растений – Фитонциды» with Kamiyama K  which was published in Japanese. This book may have served as a stepping stone for initiating research in Japan, exploring the effects of phytoncides on human well-being within the context of forest environments (森林環境), forest bathing (森林浴), forest therapy (森林療法, 森林セラピー ), and forest medicine ( 森林医学).

Glossary of Key Terms

• Phytoncides: Natural compounds released by plants that can kill bacteria, fungi, and other microorganisms.

• Fungicidal: Capable of killing fungi.

• Bactericidal: Capable of killing bacteria.

• Volatile Emissions: Substances released into the air by plants, often responsible for their scents and antimicrobial properties.

• Mitogenetic Radiation: A biological concept suggesting that certain wavelengths of light emitted by cells can influence other cells’ growth and division.

• Protozoa: Single-celled microscopic organisms, some of which can be pathogenic.

• Ciliates: A type of protozoa characterized by tiny hair-like structures (cilia) used for movement.

• Flagellates: A group of protozoa that move using whip-like structures called flagella.

• Opalina ranarum: A ciliate protozoan that lives in the intestines of frogs.

• Paramaecium caudatum: A species of single-celled ciliates commonly found in freshwater environments.

• Cytoplasmic Granulation: The appearance of small particles within a cell’s cytoplasm, often indicating cellular stress.

• Cell Lysis: The breakdown or destruction of a cell, often caused by external agents like phytoncides.

• Permeability: The ability of a substance (such as a cell membrane) to allow liquids or gases to pass through.

• Osmotic Imbalance: A disruption in the movement of water across cell membranes, which can cause cells to shrink or burst.

• Apoptosis: A natural process of programmed cell death in organisms.

• Terpene Therapy: A therapeutic practice using aromatic compounds found in plants for health benefits.

• Essential Oils: Concentrated plant extracts known for their aromatic and medicinal properties.

• Antiseptic: A substance that prevents or slows the growth of microorganisms.

• Histological Changes: Microscopic changes in tissues due to external influences, such as exposure to phytoncides.