When the atomic bomb detonated over Hiroshima at 8:15 a.m. on August 6, 1945, it killed an estimated 80,000 people almost instantly and destroyed nearly every structure within one mile of the blast. By the end of that year, the total death toll reached approximately 140,000, as thousands more died from burns, injuries, and radiation exposure in the weeks and months that followed. What happened next, in both the immediate aftermath and the decades that followed, is a story of devastation, slow recovery, and lasting consequences that still shape the city today.
The First Minutes and Hours
Survivors who were outdoors near the blast described a blinding white light followed by an overwhelming wave of heat. The fireball at the center of the explosion was so intense that dry, combustible materials like paper ignited spontaneously as far as 6,400 feet (about 1.2 miles) from ground zero. Nearly every building within a mile was leveled, and almost every structure within three miles sustained significant damage. Fires broke out across the city almost simultaneously, merging into a massive firestorm that consumed what the initial blast had left standing.
Within minutes, the mushroom cloud rose high into the atmosphere, pulling dust, soot, and radioactive debris upward. Tens of thousands of people were trapped under collapsed buildings or wandering through the ruins with severe burns. Hospitals were destroyed. Most of the city’s doctors and nurses were dead or injured themselves. The few functioning aid stations were overwhelmed almost immediately.
Black Rain and Radioactive Fallout
About 20 to 30 minutes after the explosion, a strange, dark rainfall began over parts of the city and surrounding areas. This “black rain” was sticky, heavily contaminated, and left dark stains on skin and clothing. It contained a mixture of radioactive fallout from the bomb, soil and debris churned up by the blast wave, and soot from the raging fires. Later analyses confirmed the rain carried bomb-produced radioactive material, including cesium-137, and that its uranium isotope ratios matched those of a nuclear weapon.
The rain contaminated open water sources across a wide area. Because the bombing had destroyed the city’s water pipes, survivors were desperately thirsty and drank from wells, rivers, and ponds. Fish in ponds and eels in rivers floated dead to the surface. Cattle developed diarrhea. People in some neighborhoods experienced diarrhea lasting more than three months, likely from drinking contaminated groundwater. Many survivors who were not directly exposed to the blast still suffered health effects from ingesting or being soaked by the black rain.
Radiation Sickness in the Weeks After
In the days following the bombing, a second wave of death began. People who had survived the initial blast and seemed relatively uninjured started developing strange symptoms: nausea, vomiting, bloody diarrhea, hair loss, and bleeding gums. These were the signs of acute radiation syndrome, caused by the intense burst of gamma rays and neutrons released at the moment of detonation.
The progression was often cruelest for those who appeared to recover briefly. Some survivors felt better for a few days or even a couple of weeks before their condition suddenly deteriorated. Their immune systems, ravaged by radiation damage to bone marrow, could no longer fight infection. Many died from infections or uncontrolled bleeding weeks after the blast. By the end of December 1945, the cumulative death toll in Hiroshima had reached roughly 140,000, give or take 10,000.
Long-term Cancer and Health Effects
The health consequences didn’t end in 1945. Studies tracking survivors (known in Japanese as “hibakusha”) over the following decades revealed a clear increase in cancer rates. Among those who were within about 2,500 meters of the blast and received an average radiation dose, the risk of developing a solid cancer was roughly 10% higher than normal age-specific rates. For survivors who received higher doses, the excess risk climbed sharply: at a dose of 1.0 gray (a measurement of absorbed radiation), cancer risk was about 50% above baseline, according to the Radiation Effects Research Foundation.
Overall, researchers estimated that about 848 excess solid cancers, representing roughly 10.7% of all cancers in the studied survivor population, were attributable to radiation from the bomb. Leukemia appeared first, with elevated rates showing up within just a few years of the bombing and peaking about six to eight years later. Solid tumors in the thyroid, breast, lung, stomach, and other organs followed over the next several decades. These findings became the foundation for much of what the world now understands about the health effects of radiation exposure on large populations.
A City in Ruins
In the immediate aftermath, Hiroshima was essentially a flattened wasteland. The city’s population, which had been around 350,000 on the morning of the bombing, was shattered. Infrastructure was gone. Streetcar lines were twisted, bridges were buckled, and the few concrete buildings still standing were burned-out shells. Survivors lived in makeshift shelters built from wreckage. Food and clean water were scarce, and aid from outside the city was slow to arrive, partly because the extent of the destruction was difficult for anyone to comprehend from a distance.
The Japanese military and government initially struggled to understand what had happened. It took some time before the full nature of the weapon was recognized. When journalists and investigators reached the city, the scale of the devastation was unlike anything previously documented in warfare.
Rebuilding as a “Peace Memorial City”
Reconstruction began slowly, but it gained momentum after the war ended. In 1949, Japan’s national government passed the Hiroshima Peace Memorial City Construction Law, a piece of legislation written specifically for one city. The law designated Hiroshima as a symbol of the pursuit of lasting world peace and provided special financial support from the national government. It also transferred former military land and other nationally owned property to the city to aid rebuilding.
The city was redesigned with wider streets, more parks, and modern infrastructure. The area around ground zero was transformed into Peace Memorial Park, which today includes a museum, monuments, and an eternal flame that will burn until all nuclear weapons are eliminated. One ruin was deliberately left standing: the domed skeleton of what had been the Hiroshima Prefectural Industrial Promotion Hall, located almost directly below the point of detonation. Through the efforts of the city and its residents, this structure, known as the Genbaku Dome (or Atomic Bomb Dome), was preserved in the same condition it was in immediately after the blast. Minimal reinforcement with steel and synthetic resin was added during conservation projects in 1967, 1989 to 1990, and 2002 to 2003. In 1996, UNESCO designated it a World Heritage Site.
Hiroshima Today
Modern Hiroshima is a thriving city of over 1.1 million people, the largest in the Chugoku region of western Japan. It has a professional baseball team, a well-known food culture centered on okonomiyaki (savory pancakes), and a busy economy built around manufacturing, technology, and tourism. Millions of visitors come to the Peace Memorial Park each year.
The city is not radioactive today. Unlike a nuclear reactor meltdown, which can leave long-lasting ground contamination, the Hiroshima bomb detonated high in the air (about 1,900 feet above the city). This meant the intense radiation was delivered as a single flash rather than as persistent contamination soaked into the soil. Residual radioactivity from fallout and the black rain faded relatively quickly, and the area was safe for habitation within a matter of years.
The hibakusha, now elderly, have spent decades sharing their stories and advocating for nuclear disarmament. Their testimony, along with the physical evidence preserved in Hiroshima’s museums and the Genbaku Dome, remains the most direct record of what a nuclear weapon does to a city and its people.