The "Summer Onkatsu" Boom Loved Even in Extreme Heat: Behind the Scenes of Belly Warmers, Summer Heat Patches, and Warm Innerwear That Save You from Air Conditioning Chill

Table of Contents

1. Introduction: An Era Discussing "Chill" in Midsummer

2. What is Onkatsu? Definition and History of Summer Onkatsu

3. Market Expansion Through Data

4. In-depth Look at Hit Products (Belly Warmers/Summer Kairo/Warm Eye Masks, etc.)

5. Manufacturer Development Interview

6. User Roundtable: How Onkatsu Differs Between Gen Z and Those in Their 40s

7. Doctors Explain the Mechanism and Countermeasures for "Summer Chill"

8. Business Perspective: Analyzing Winning Strategies in Retail and E-commerce

9. Sustainability and Reusable Onkatsu

10. Experts Propose! Summer Onkatsu Protocols That Suit You

11. Summary and Future Outlook

1. Introduction: An Era Discussing "Chill" in Midsummer

In the summer of 2025, where scorching days over 35°C have become the norm, people sweat profusely outside but feel chilly once they enter offices or trains. This temperature difference stress is being viewed as a problem as it leads to autonomic nervous system disorders and gastrointestinal issues. TBS's information program 'THE TIME,' reported this morning that "sales of summer kairo have increased fivefold compared to last year," surprising market stakeholders.TBS NEWS DIG

1-1 Voices of the Consumers

• "Even with the air conditioner set at 28°C, my feet feel like ice" (Female, 20s)

• "I often get stomach issues due to the chill. I can't do without a thin belly warmer" (Male, 30s)
  With the spread of telework, the cost of chill countermeasures has shifted to individuals.

2. What is Onkatsu? Definition and History of Summer Onkatsu

"Onkatsu" refers to lifestyle habits that raise body temperature and promote blood flow and metabolism, which became popular as a winter beauty trend in the 2010s. It is now applied to the **“air conditioning chill” season**, with five categories becoming the main players in summer onkatsu: ① adhesive kairo, ② belly warmers and leg warmers, ③ warm foods (ginger and mugwort steaming), ④ electric heated wear, and ⑤ warm sensation gadgets.

Rakuten's press release positions "Summer Onkatsu" as a pillar of the 2025 trend, offering cross-sectional proposals from household goods to food and beauty.Rakuten Group, Inc.kufura (Kufura) Shogakukan Official

3. Market Expansion Through Data

3-1 The Impact of Fivefold Sales

A buyer from Shibuya Loft revealed, "The adhesive type summer kairo is about five times compared to the same week last year." The same figure was confirmed in TBS reports.TBS NEWS DIG

3-2 Trends in E-commerce Malls

The EC analysis service "Nint" reports that the disposable kairo market is worth 150 million yen even in summer, with a 128% increase compared to 2023, indicating that summer demand is beginning to establish itself as a "hidden peak."Press Release & News Release Distribution Share No.1｜PR TIMES

3-3 Rakuten Market Research

• Onkatsu-related distribution amount: Annual 1.2 times → Summer 1.3 times, surpassing winter

• Purchase reasons: Air conditioning chill countermeasure 72%, metabolism boost 55%, energy saving 22%

• Gender ratio: Women 68% and men 32%, with an expanding male ratioRakuten Group, Inc.kufura (Kufura) Shogakukan Official

4. In-depth Look at Hit Products

Detailed specs and reviews were featured in 'THE TIME,' and Omoshirogaru special.Omoshirogaru!TBS NEWS DIG

5. Manufacturer Development Interview

Kowa Co., Ltd. (Summer Kairo Development Team)

"Even in midsummer, 45–50°C is the 'just right' temperature range. We reduced the heating agent composition by 38% from the winter version, designed to prevent low-temperature burns even when attached to the back of thin clothing" (Development Manager, Mr. Sasaki)

SOWAN (Belly Warmer Brand)

"Balancing sweat absorption and quick drying with far-infrared radiation was a challenge. We blended 54% silk and 46% far-infrared thread, keeping the thickness to 1 mm" (Product Planning, Mr. Yamada)

6. User Roundtable

• Gen Z says "Chill is tough in cafes and trains" and "Onkatsu posts on Instagram"

• Women in their 40s say "Menopause support" and "Relax with mugwort steaming"

• Male Office Workers say "Set room temperature higher for energy saving and use kairo together"
  . Word of mouth spreads on TikTok, with the SNS tag "#SummerOnkatsu" exceeding 30,000 posts in the past month.

7. Doctors Explain the Mechanism of "Summer Chill"

Dr. Yoshioka from Tokyo Women's Medical University points out, "When skin temperature drops below 32°C in air-conditioned environments, the sympathetic nervous system becomes overactive, causing peripheral blood vessels to constrict. The drop in core body temperature can lead to decreased immune function and gastrointestinal disorders."Local warming to return skin temperature to around 36°C can make the parasympathetic nervous system dominant, potentially improving sleep, he says.

8. Business Perspective: Analyzing Winning Strategies in Retail and E-commerce

• Physical Stores: Tokyu Hands has moved the "Chill Countermeasure Corner" to the center layout, increasing customer unit price by 22% with cross-merchandising of summer kairo, thin innerwear, and onkatsu tea

• E-commerce Malls: Rakuten guided searches for "summer belly warmer" with official ads, doubling click-through rates

• D2C: USB-type thermal gadget companies raised 10 million yen through crowdfunding, setting reward shipments for August to create buzz

9. Sustainability and Reusable Onkatsu

Disposable kairo, containing iron powder and activated carbon, are treated as combustible waste, but some municipalities are using recycled powder as soil improvement material. Meanwhile, rechargeable kairo can be used 500 times, reducing CO₂ emissions by 75% (manufacturer estimate). The environmental orientation of onkatsu users will influence the future market.

10. Experts Propose! Summer Onkatsu Protocols That Suit You

1. Desk Work Under Air Conditioning: Belly warmer + one adhesive kairo (waist)

2. Home Telework Energy Saving: Thin leg warmers + hot water maker

3. Before Bed: USB eye mask + neck warmer

4. Outdoor Leisure: Rechargeable kairo (also serves as a mobile battery)

5. Poor Circulation Type: Double onkatsu with ginger tea & mugwort steaming

11. Summary and Future Outlook

The summer of 2025 has seen the emergence of the paradoxical demand to "warm up despite the heat," with summer onkatsu goods becoming established as the "second cool sensation products." Manufacturers are accelerating product development with a trinity of low-temperature safety design, moisture-absorbing heat-dissipating materials, and USB power supply. Users can enjoy multifaceted values such as health maintenance, energy saving, and relaxation.

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