A kaya (mosquito net) is a box-shaped net that offers protection against harmful insects such as mosquitoes. They are normally hung indoors.
In order to exclude insects but allow air to pass, mosquito nets are comprised of a 1mm mesh and were originally made from materials such as hemp and later from synthetic fibers.
The mosquito net arrived in Japan via China. It was initially used by the nobility but its use spread to the common people during the Edo period. Mosquito net peddlers with their call of "Kaya! Moegi no kaya!" (lit. Mosquito nets! Light green mosquito nets!) were an indication that summer had arrived in Edo.
They are often used at bedtime and in order to allow them to be easily mounted and dethatched, a hook would be attached to a depression in the nageshi (beam running between columns) in traditional Japanese rooms. Another method was attach a hook to the nageshi from which a to hang a circular frame. Such nageshi are rarely seen in modern Japanese homes.
Mosquito nets fell almost completely out of use by the latter half of the Showa period as a result of changes to living conditions including decreased numbers of mosquitoes due to pesticides and drainage, the increased use of screen doors that accompanied the popularity of airtight aluminum frames, as well as the diffusion of air conditioning.
Their use has started to become reevaluated from the standpoints of ecology and chemical allergies as they represent a mosquito repellent that uses neither electricity nor chemicals.
There are also areas outside of Japan where the use of mosquito nets is becoming widespread. In various African and Southeast Asian countries afflicted by malaria, mosquito nets have gained attention as a low-cost measure against mosquitoes.
Following a request by the World Health Organization (WHO) to increase mosquito net production and voluntary export of technology to Africa, Sumitomo Chemicals Co., Ltd. constructed two factories in Tanzania in the year 2000.
From 2003 in Japan, support was implemented through official development assistance and UNICEF, and over two million mosquito nets were distributed throughout the world in three years.
The spread of mosquito nets in Nigeria has advanced as a result of publicity from television drama series and commercials.
The WHO provides mosquito nets containing the pyrethroid insecticide as overseas aid. These have the effect of killing mosquitoes which come into contact with the net and remain effective for a period of five years.
Because of indications that pyrethroid may be carcinogenic, there is an emerging opinion that advocates the use of mosquito nets without chemicals added.
There are upside-down umbrella shaped foldable mosquito nets designed for infants and dining tables.
Those designed to temporarily protect food, even those with the same dome shape as described above, are called mesh food covers.
There is a Japanese expression that goes 'kaya no soto' (lit. 'outside of the mosquito net') which refers to the withholding of important information or leaving somebody out of a group.
A haiku poem by Issa KOBAYASHI reads, 'Atarashiki, Kaya ni nerunari, Edo no uma' and translates as 'A horse in Edo sleeps under a new mosquito net.'