Runners collapsing in killer heat: Seoul warns of heat illness risk during exercise

A significant number of heat illness patients treated in Seoul this summer fell ill while running, prompting city officials to urge extra caution as the running boom shows no signs of cooling despite extreme heat.

According to the Seoul Metropolitan Government, 185 people in Seoul were treated for heat-related illness between May 15, when the Korea Disease Control and Prevention Agency's heat illness surveillance system was activated, and Monday.

Yeongdeungpo-gu recorded the highest number of cases among Seoul's 25 districts, with 29 patients in total. Of those, 20 — or 68 percent — sought hospital care after participating in marathon events held in May and June, before the worst of the summer heat had set in, at venues including Yeouido and Han River parks. Many lost consciousness.

On Monday, a participant in a nighttime walking event at a Han River park in Yeongdeungpo-gu was also hospitalized for heat illness after walking for three hours. Heat illness refers to acute conditions caused by heat exposure, with heat exhaustion and heatstroke among the most common. Without prompt treatment, it can lead to loss of consciousness and become life-threatening.

In Mapo-gu, which ranked second in heat illness cases, 11 of 14 patients had also attended marathon events in May and June before seeking hospital care. All of those cases occurred between 9 and 10 a.m.

Yeongdeungpo-gu also led all 25 districts last year with 43 heat illness cases, while Mapo-gu came in second with 32. A Seoul Metropolitan Government official said the high numbers are likely linked to the growing number of people running near Yeouido, Han River parks and the area around the World Cup Stadium in Sangam.

As of Sunday, 162 heat illness cases had been recorded in Seoul this year, and the 10–11 a.m. slot had the highest number at 21. The hottest hours — 1–2 p.m. and 2–3 p.m. — saw fewer cases, with 13 and 15 respectively. "Looking at the overall distribution of cases across Seoul, the morning hours account for the most," a city official said. "We believe many of these cases are occurring during exercise."

The running population has jumped sharply. A Gallup Korea survey on participation rates in 15 outdoor and indoor activities, released in October 2024, found that jogging and running had seen the fastest growth of any activity in recent years. The share of people who reported jogging or running in the past year rose steadily from 23 percent in 2021 to 27 percent in 2022 and 32 percent in 2023.

Marathon participation has also surged. Data the Korean National Police Agency submitted to the National Assembly's Culture, Sports and Tourism Committee last October showed that 254 marathons were held in South Korea in 2024, drawing about 1.008 million participants. Annual marathon participation started at around 9,000 in 2020, then climbed to about 30,000 in 2021, about 320,000 in 2022 and about 730,000 in 2023. The Ministry of Culture, Sports and Tourism's 2025 National Sports Participation Survey also found that the share of people jogging and running jumped from 4.8 percent in 2024 to 7.7 percent last year.

In Seoul, five marathons were held last month as the summer heat set in, and five more are scheduled this month.

The Seoul Metropolitan Government has also been promoting running through programs such as "Swieomswieom Morning," a Seoul-style recreational sports program that — unlike competitive marathons — welcomes participants at their own pace and fitness level, whether walking, running, cycling, pushing a stroller or bringing a pet. After a pilot run in March, the program moved to regular operation last month. A total of 6,807 residents have taken part so far, on a Han River course between Yeouido and Mapo Bridge and a downtown course running from Seoul Plaza along Sejong-daero to Sungnyemun.

"To prevent heat illness, runners and marathon participants need to stay well hydrated and take adequate rest," a Seoul Metropolitan Government official said.