Katori senkō: The Mosquito insense Coil in Japan

A mosquito coil is mosquito-repelling incense, usually made into a spiral, and typically made from a dried paste of pyrethrum powder.

The coil is usually held at the center of the spiral, suspending it in the air, or wedged by two pieces of fireproof nettings to allow continuous smoldering. Burning usually begins at the outer end of the spiral and progresses slowly toward the center of the spiral, producing a mosquito-repellent smoke.

A typical mosquito coil can measure around 15 centimeters (6 in) in diameter and lasts around 7–12 hours. Mosquito coils are widely used in Japan, Asia, Africa, South America, and Australia.

The History Of The Mosquito Coil

In Japan, during the summer months, mosquitoes can be a real problem.
Repellents for mosquito's using Pyrethrum has been used for centuries as an insecticide.

The in the late 1800s however a Japanese businessman, Eiichiro Ueyama, invented the first Pyrethrum mosquito coil, which he patented in 1895.

A man named Ueyama Eiichiro, who was in the business of exporting mandarin oranges when Fukuzawa Yukichi, the famous author, statesman, and founder of Keio University, introduced him to a seed trader in the United States. This dealer offered Ueyama seeds of a flowering plant that he claimed would knock insects dead.

Ueyama decided to import the seeds and start growing the plant in Japan. It was a member of the aster family, Tanacetum- cinerariifolium, and certainly didn’t look like a killer.
With two rows of overlapping white petals and a cheerful yellow center, the flower resembled nothing so much as the common daisy. But sure enough, there was something in the flower heads, when dried and ground into a powder, that proved lethal to insects.

Ueyama called the plant jyochūgiku (which I’ll translate with a little liberty as “bug-banishing chrysanthemum”) and built a business that is still a leader in pest control today.

Birth of "Kinchoko"

He devised to knead pyrethrum, which is the active ingredient, into incense sticks, and in 1890, the world's first rod-shaped mosquito coil "Kinchoko" was born.
The mosquito coil at the beginning of development was rod-shaped, but since it was used upright from its shape, there was a possibility of fire if it fell down, and the burning time was short about 40 minutes.

Ueyama's wife Yuki proposed making the sticks thicker and longer, and curling them in spirals, in order to make them last longer and in In 1902, after a series of trials and errors, he achieved an incense burning effect with a spiral-shape.
By changing the shape, the burning time has been extended to 7 hours, and the safety has been improved by laying it down.

Usage

You light the outer end of the spiral and it burns slowly, progressing toward the center, emitting a mosquito-repelling smoke. There are different sizes and types, but a coil that is 75 cm long and 10.5 cm in diameter will provide protection for about seven hours.

To use a mosquito coil, you first place it in a holder to keep it safe and off the ground where it can get air to burn.

Simple holders are often included with the coils, but some people get quite particular about what they use to contain their coils, with pig-shaped ceramic holders being a perennial favorite.

The Ingredients of The Mosquito Coil

Some examples of active pyrethroids used in making mosquito coil include pynamin forte, allethrin, d-allethrin, and ETOC. In addition to pyrethroids, mosquito coils may also contain a pesticide such as DEET.
Approved by the EPA, DEET is one of the most commonly used ingredients in insect repellent products, including mosquito coils. A common misconception that many people have is that DEET kills bugs. It does not. Instead, it makes it harder for bugs to smell humans, reducing the risk of bites.

In addition to chemical compounds, mosquito coils may also include essential oils such as thyme, soybean oil, clove oil, picaridin, citronella, and citrus extract.
These are designed to improve the smell of the coil.

Effects On Mosquito's

The active compound, originally obtained from the jochūgiku flower although it can now be synthesized, is called pyrethrin. It occurs naturally in the seed cases of the flowers and has powerful insecticidal activity.
In small doses, it repels insects and in higher concentrations, it kills them by attacking their nervous systems. Pyrethrin is a very common ingredient in insecticides around the world.

Disadvantages of mosquito coils

Some coils sold were found to produce as much smoke PM2.5 as 75-137 burning cigarettes and formaldehyde emission levels in line with 51 burning cigarettes.

Coils are not a significant health risk, although some organisms may experience temporary sensory irritation like that caused by smoke from the combustion of organic materials such as trees and plants.
In such environments, the smoke from mosquito coils can be irritating so the company developed no-smoke alternatives.

While mosquito coils are not harmful in the short term to humans, scientific studies show that sustained use of mosquito coils can lead to breathing issues such as wheezing and asthma.

Improved product

In the 1960s, The Japanese invented devices that plug into electric outlets and diffuse mosquito repellents into the air, replenished by changing a small mat or liquid dispenser.

More recently they’ve added a spray that can protect a room from mosquitoes for up to 12 hours with a single pump.

Post Scriptum

On a personal, I have lived in Japan for over a decade, and nothing says “summer in Japan” to me, right up there with kakikōri (shaved ice) and the Koshien like the sight and smell of those once-ubiquitous green mosquito coils.
I realized this year that I don’t see them as much as I used to... I wonder why that is? interesting thought to ponder on...
More so in rural areas, I noticed many Japanese feel very nostalgic about Katori senkō, and the time when life was slower in Japan.