Koromogae: How Japan Swaps Its Wardrobe, and Its Mood, With the Seasons

On the morning of 1 June, something changes on Japanese streets all at once. Students who wore dark wool blazers the day before appear in white short-sleeved shirts. Office workers loosen their ties or drop them, and shop staff swap into lighter uniforms. On 1 October, the whole scene reverses. This twice-a-year turn of the wardrobe is called koromogae, literally a change of clothes.

This guide explains where koromogae came from, from the court of the Heian period to the Meiji government, how it works today in schools and workplaces, and how kimono follow their own seasonal calendar. It also covers the Cool Biz campaign, the household habit of rotating clothes, and a few tips for dressing well when you visit Japan in the months around each change.

What Koromogae Means

Koromogae combines koromo (clothes) and kaeru (to change). It marks the move from winter clothing to summer clothing on or around 1 June, and the move back on 1 October. In its narrow sense, the word refers to the changing of uniforms for students, company workers and officials such as police and firefighters. In its wider sense, it covers every household's habit of putting away one season's wardrobe and bringing out the next.

The change follows the calendar, not the thermometer. Schools and companies with uniforms switch on the set date regardless of the actual weather, and many allow a transition period (iko kikan) of one or two weeks, during which people may wear either summer or winter clothing. That flexibility is welcome in a country where a late May heat wave or a cool early June is common. Dates are often adjusted by region, with colder areas such as Hokkaido switching later and warm southwestern areas switching earlier.

From the Heian Court to Meiji Law

The custom is said to have come from China and became an imperial event in the Heian period (794 to 1185). At the court, summer clothing was worn from the first day of the fourth lunar month and winter clothing from the first day of the tenth. The change was called koi, and the lady-in-waiting who looked after the imperial wardrobe shared the same name, so the public came to call the custom koromogae. In the Kamakura period (1185 to 1333), the seasonal changes widened to furnishings, decorations and tableware.

In the Edo period (1603 to 1868), the Tokugawa shogunate required samurai to change their clothes four times a year, switching between lined kimono (awase), single-layer kimono (katabira) and padded garments (wataire) on set dates. Farmers, craftspeople and merchants had no such strict rules and dressed for their work and climate. After Japan adopted the solar calendar in 1873, the Meiji government fixed a twice-a-year schedule: summer clothing from 1 June to 30 September and winter clothing from 1 October to 31 May. Western-style uniforms for public servants, police and the military followed this timetable, and it spread to school uniforms and the general public.

Uniforms, Schools and Workplaces

Today the most visible koromogae happens in schools. Students in seifuku (school uniforms) switch to their lighter summer versions on 1 June and back to heavier ones on 1 October, which makes the change a shared seasonal milestone for millions of families. Department store and shop staff, transport workers and others in uniform follow similar patterns, and companies with strict dress codes may use the same dates.

The switch changes more than sleeve length. Colors, fabrics and layers change too, and stores renew their seasonal collections to match. Before putting winter clothes away, many people take coats to the dry cleaner so they will be fresh next autumn. Some observers note that fewer people follow the custom strictly now, citing air conditioning and warmer weather, while others still value the chance to tidy up, rethink their style and feel closer to the seasons.

The Household Clothes Rotation

At home, koromogae is a small seasonal chore with a pleasing logic. People wash the previous season's clothes, store them in boxes or drawers with moth repellent, and bring out the clothes for the new season. Some households also use the day to clean the house and rearrange the rooms, because in Japanese tradition a season is something to prepare for.

The idea reaches into other parts of life as well. In formal settings such as the tea ceremony, kimono patterns and colors, and even the utensils and furniture, are changed to match the season. In haiku, koromogae is a recognized seasonal word, and by convention it points to the shift to lighter summer garments, a sign of leaving winter behind.

Kimono and the Seasonal Calendar

Kimono follow an even finer seasonal calendar. According to one kimono house, the lined type called awase is worn for about six months, from October through May, and is the most standard type of kimono. The unlined type called hitoe is worn in June and September as a transition, and sheer summer kimono called usumono are traditionally worn in July and August. Timing varies by region and weather, and many people now start wearing lighter garments earlier as the warm season lengthens.

For formal events such as weddings and ceremonies, it is generally expected that the traditional seasonal canon is followed. That is why you may see a kimono in a light, breezy fabric in midsummer and a richer lined one in autumn. Kimono shops and rental studios will gladly explain what suits the month, and a visit to one is a good way to see the calendar in fabric.

Cool Biz and a Modern Twist

In 2005, Japan's Ministry of the Environment, led by Minister Yuriko Koike under Prime Minister Junichiro Koizumi, launched Cool Biz, a campaign urging offices to set air conditioners to 28 degrees Celsius and encouraging workers to leave off jackets and ties. It was widely welcomed, and it gave the summer part of koromogae a new look: short sleeves, open collars and light fabrics became acceptable in many workplaces. The campaign originally ran from June to September and has since been lengthened.

A winter counterpart, Warm Biz, suggests warm layers such as vests and sweaters. In 2011, a Super Cool Biz version allowed even more casual outfits, including polo shirts, in a drive to save electricity. These campaigns show how an old custom can adapt: the clothing calendar remains, but its rules bend to modern needs for comfort and energy saving.

Dressing for the Seasons as a Visitor

If you travel in Japan around the turn of the seasons, you will see koromogae in action. Around 1 June and 1 October, groups of students in fresh uniforms are a reliable sign that a new season has arrived. In late May and early June, expect warm days and humid air, so light, breathable fabrics are a good choice. In October, mornings and evenings cool quickly, so a light jacket or cardigan is handy.

There is no rule for visitors, and you can wear what feels comfortable. Still, matching the local rhythm has a charm. Pack layers, check the forecast for the city you are visiting, and notice how many people around you dress by season rather than by the day's weather.

Tips for Visitors

Plan for the transition weeks. In the first half of June, some people may still wear long sleeves while others have changed, so there is no single look. At shrines, temples and formal restaurants, neat and modest clothing is always welcome, in any season. Bring an umbrella for the early summer rainy season, and carry a small towel or handkerchief for warm days.

If you would like to join the tradition, try a small koromogae of your own: wash your coats at the start of summer, store them carefully, and bring out lighter clothes with a fresh start. For current dress guidance at specific events or venues, check the official website of the place you plan to visit.