[First Year of 'Extreme Heat Days' in 2026] Which Diseases to Watch Out for in Severe Heat? Clinic For Announces '3 Major Ailments of the Extreme Heat Season'

Clinic For Group, which provides in-person and online medical consultations, has compiled key points for medical visits and 'lifestyle-related ailments' that increase during the extreme heat season, ahead of the summer of 2026—the first summer since the Japan Meteorological Agency (JMA) newly defined 'Extreme Heat Days' (days with a maximum temperature of 40°C or higher).

Diseases to watch out for during severe and extreme heat include skin problems such as eczema and heat rash, cholinergic urticaria/sweat urticaria triggered by sweating, increased body temperature, or exercise, and summer shingles, which reactivate due to weakened immunity caused by fatigue accumulation from extreme heat or exposure to strong UV rays. Clinic For has summarized countermeasures for these symptoms and conditions often overlooked during the extreme heat season as the '3 Major Ailments of the Extreme Heat Season'.

[Background] 2026 is the First Year of 'Extreme Heat Days' Adopted by JMA—Temperatures Nationwide Forecasted to Be Higher Than Average, with Heat Arriving Early

According to the JMA's warm season forecast (announced February 24, 2026), temperatures from June to August 2026 are expected to be higher than average nationwide, with the risk of severe heat in various regions. Weathernews analysis (*1) indicates that the Pacific high-pressure system will expand early, bringing an earlier onset and end to the rainy season, earlier arrival of heat, and the possibility of record-breaking severe heat due to overall global atmospheric temperature rise.

'Extreme Heat Day' is a term officially adopted by the JMA on April 17, 2026, reflecting three consecutive summers of significantly high temperatures (selected with the most votes, approx. 202,000 out of 478,000 from 13 candidates). In 2025, Japan recorded a historical high of 41.8°C (Isesaki City, Gunma Prefecture), and temperatures over 40°C were observed at a total of 30 locations (a record high). With a significant likelihood of severe heat again in 2026, leading to potential 'Extreme Heat Days', daily life preparedness and early medical consultations become more critical.

*1 Weathernews 'Summer 2026 [Warm Season Forecast] Temperatures Higher Nationwide, Beware of Severe Heat Again This Summer' (Feb 24, 2026)

Summer 2026 Severe Heat Forecast | Weather Data Summary

- JMA Warm Season Forecast (Announced Feb 24, 2026) *2: Temperatures from June to August 2026 expected to be higher than normal nationwide. Pacific high-pressure expansion near Honshu likely to strengthen, posing a risk of severe heat. Precipitation normal nationwide, but the June-July rainy season tends towards higher rainfall in Kyushu to Tohoku (40%).
- Weathernews Summer 2026 [Warm Season Forecast] (Feb 24, 2026) *1: Early expansion of the Pacific high, earlier rainy season, and early arrival of heat expected. Potential for record severe heat due to global atmospheric temperature rise. Some areas may observe mid-summer days of 30°C+ before the Golden Week holidays.
- JMA 'Extreme Heat Day' Term Decision (Press Release Apr 17, 2026) *3: Days with a max temperature of 40°C+ named 'Kokushobi' (Extreme Heat Day). Adopted from approx. 202,000 votes. In 2025, over 40°C recorded at 30 locations, including the national record 41.8°C.

*2 JMA Seasonal Forecasts
*3 JMA Press Release on 'Extreme Heat Day' Naming

[In-Depth Analysis] 3 Major Ailments to Watch Out for in the 2026 Severe Heat: Eczema / Summer Hives / Summer Shingles

Among signs often ignored as 'just summer fatigue' or 'it will heal soon', some can be prevented from worsening by consulting a medical institution early. Clinic For summarized three ailments often overlooked:
1. Adult Eczema/Heat Rash (Severe Heat Eczema)
2. Summer Hives (Cholinergic Urticaria / Sweat Urticaria)
3. Summer Shingles

Both 1 and 2 appear as skin signs but have different mechanisms (1 is a skin barrier disruption from sweat, friction, or UV; 2 is an allergic reaction triggered by sweat, body heat, or exercise). For 3, shingles, the vaccine became a routine vaccination for ages 65 and over in April 2025 (with transitional measures). Those aged 50 and over can receive it voluntarily. Interest in shingles onset risk is growing towards summer 2026.