President Donald Trump's recent warning about the possibility of Iranian attacks on U.S. cities has renewed attention on the potential consequences of a nuclear explosion, including the devastating effects such an event could have on the human body.

During a rally in Nebraska, Trump referred to Los Angeles and San Diego while discussing the ongoing conflict with Iran, drawing criticism from California officials. The White House later said his comments had been misunderstood.

While Trump did not specifically say a nuclear weapon would be used, his comments have renewed attention on the potential consequences of a nuclear explosion and what it could do to the human body.

The answer depends largely on the size of the explosion, a person's distance from it and whether they are indoors or outdoors. A nuclear detonation can expose people to several different hazards at once, including intense heat, a powerful blast wave, radiation and radioactive fallout.

A Nuclear Blast Can Cause Severe Burns and Traumatic Injuries

The first injuries would not necessarily come from radiation.

A nuclear explosion produces an intense pulse of heat, light and air pressure. People close to the blast can suffer severe burns, eye injuries and trauma from the pressure wave itself. Buildings and other structures can also collapse, causing blunt-force injuries, fractures and penetrating wounds from flying debris.

The eyes can be particularly vulnerable. Looking directly toward a nuclear flash can cause temporary blindness or, at high enough exposure, burns to the retina. The intense heat can also produce serious skin burns depending on the person's distance from the explosion.

Radiation Can Damage the Body at the Cellular Level

Beyond the immediate blast, ionising radiation can damage cells by disrupting biological molecules, including DNA.

A sufficiently high dose received over a short period can cause acute radiation syndrome (ARS), also known as radiation sickness. According to the Centers for Disease Control and Prevention (CDC), ARS generally requires exposure to a high dose of penetrating radiation involving the whole body or most of it over a short period.

The earliest symptoms can include nausea, vomiting, headache and diarrhoea. They may begin within minutes to days, depending on the radiation dose.

Radiation can also damage tissues with rapidly dividing cells. The bone marrow, for example, can be severely affected, reducing the body's production of blood cells. This can leave a person vulnerable to infections and potentially life-threatening bleeding.

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Radiation Sickness May Seem To Disappear Before Getting Worse

One of the more deceptive aspects of severe radiation exposure is that a person may initially appear to recover.

After the first wave of symptoms, some people enter a latent period during which they may feel relatively well even as radiation-related cellular damage continues. The CDC describes this as one of the stages of ARS. The illness can later return with symptoms depending on the tissues affected and the dose received.

At very high exposures, radiation can severely damage the gastrointestinal tract or the cardiovascular and central nervous systems. These forms of radiation injury can cause severe diarrhoea, dehydration, neurological symptoms, seizures, loss of consciousness and, in the most extreme cases, death within days.

Radiation can also injure the skin. Redness, itching, tingling and swelling may appear hours to days after exposure, with more severe injuries potentially causing blistering or ulcers.

Fallout Can Create Longer-Term Health Risks

The danger does not necessarily end after the initial explosion.

Radioactive material can become incorporated into fallout and contaminate the surrounding environment. People can be exposed externally by radioactive material around them or internally by breathing contaminated air or consuming contaminated food or water.

The severity of radiation-related illness depends on factors including the radiation dose, type of radiation, route of exposure and duration of exposure. Lower doses may not cause immediate radiation sickness but can still increase the long-term risk of cancer.

Infants, children, older adults, pregnant women and people with weakened immune systems can be particularly vulnerable to some effects of radiation exposure.

For people outside the immediate blast zone, following official emergency instructions is critical. During a radiation emergency, the CDC advises people to remain inside a building or designated shelter until authorities say it is safe to leave, unless there is an immediate life-threatening danger such as a fire or building collapse.

A nuclear explosion therefore presents not one medical threat but several: traumatic injury from the blast, burns and eye damage from intense heat and light, acute radiation sickness from high-dose exposure and potentially increased cancer risk from longer-term radiation exposure. How severely the body is affected ultimately depends on the dose and the person's circumstances during and after the event.

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