字幕表 動画を再生する 英語字幕をプリント Radiation sickness might sound like something out of a post-apocalyptic horror film. And it often is. It's been portrayed in movies and television for more than 50 years. And those portrayals vary a lot. I mean, the fate-worse-than-death described in 1959's On the Beach is very different than the 'based on a true story' version depicted in the 2019 miniseries Chernobyl. But if there's one thing pretty much all these portrayals have in common, it's that they get radiation sickness wrong—at least somewhat. Like, people don't just start oozing blood out of their legs, and you can't get the illness from hugging a hospitalized loved one. To start off, technically, radiation sickness is called Acute Radiation Syndrome or ARS. And it's not one thing, but rather, a bunch of different syndromes that result from being exposed to large doses of ionizing radiation. That's the kind of radiation that carries enough energy to knock electrons off of atoms. And it's a problem for your cells, because all that energy can break chemical bonds and therefore mess with essential molecules like DNA. Your cells have ways of fixing broken molecules, of course, especially breaks to DNA. But they aren't perfect, so ionizing radiation often leads to mutations. And let's be clear: cells don't become better from these mutations. The more radiation-induced mutations a cell has, the more likely it is that it will die or become cancerous. So although radiation can change your DNA, it isn't going to turn you into a walking, roaring, city destroyer a la Godzilla, or give you superpowers. I'd hope that radiation myth was pretty obvious, but not all of them are so easy to spot. For example, let's say a person walks into the exact wrong room and is exposed to a lot of radiation. And by a lot, I mean enough that this person gets more than 0.7 grays of radiation exposure from spending five minutes in that room. A gray is a measure of how much energy is absorbed by an object or person per kilogram of weight. And though it might not sound like much, 0.7 grays is a lot. For comparison, when you get a chest x-ray, you absorb about 0.0001 grays, and a full-on CT scan exposes you to just 0.01 grays. So, yeah, 0.7 grays is a lot of radiation, and this person has just been exposed to it. What happens next? Based on Hollywood, you might think their skin will instantly blister or they'll start bleeding from everywhere. But that's not how radiation sickness works. They might have no symptoms for a while. Depending on the exposure, it could take minutes to hours before they enter what's called the prodromal stage of ARS. At this point, they might feel nauseous or vomit, or have a fever, headache, or diarrhea. Symptoms like these can happen on and off for a few days. And we're not entirely sure why that happens. The best explanation we have is that radiation somehow activates cells in the gastrointestinal tract to release the neurotransmitter serotonin, and that triggers the brain's vomit center. A similar thing can happen when people get chemotherapy. What's weird about ARS, though, is that after this period of queasiness, people often feel a lot better. This is what's known as the latent stage. And as the name implies, during this phase, it might not seem like there's a lot going on. A person who's been exposed can feel generally healthy… but they're not. Oddly enough, this is the stage where cells are actually dying. You see, the cells that die from radiation generally don't die right away. DNA damage mostly becomes a problem when cells go to divide and realize they can'ｔ, because the DNA has breaks in it or the coding sequence is wrong. So the length of the latent period partially depends on where the radiation damage occurred and how often the affected cells divide. That's why, when symptoms start to show up, they often appear in places like the intestines, bone marrow, or skin, because those tissues contain cells that divide the most often. Of course, how long the latent period lasts also depends how strong the dose of radiation was. Higher doses over a shorter period of time mean more damage, faster. Now, the latent period might sound similar to the incubation period of other illnesses where a person doesn't show symptoms, but they can transmit the disease to someone else. But, unlike TV shows would have you think, people with ARS aren't dangerously radioactive. Their radiation sickness isn't contagious. You could, say, sit by the bedside of your dying partner for days or even weeks, and you wouldn't develop ARS yourself. Now, it is possible for a person to be emitting dangerous amounts of radiation right after they've left the exposure site, because radioactive material can stick to their skin and clothes. But once those clothes are removed and their skin is thoroughly washed, the danger is gone— even if there's still radioactive material inside them. If they inhaled or swallowed bits of ash, for example, they might have stuff emitting ionizing radiation inside their body. But, even though any radioactive material inside them will continue to give off radiation until it fully decays, that radiation is lost so quickly to nearby cells that the person doesn't pose a danger to others. Basically, it's just hurting them. So, technically, you could go ahead and hug a loved one who's been hospitalized with ARS. But it might not be a good idea to do that—for their sake. You see, the radiation may have killed off a lot of the stem cells in bone marrow that make white blood cells. And those white blood cells are the immune system's army, so without them, the immune system is weakened and the person is vulnerable to infection. Plus, damage done to other tissues — like connective tissue and blood vessels — can eventually cut off the bone marrow's blood supply. And without blood, the bone marrow keeps dying even after the radiation threat has passed. Eventually, the body can't compensate for the cell damage anymore. And that that point, the person enters the manifest illness stage. This stage lasts anywhere from a few hours to several months, and looks different depending on the kinds of tissues that were damaged. Some forms of radiation syndrome show up in the skin, which can get dry, red, or itchy, or in severe cases can start to blister. Basically, it's the same idea as a sunburn—though, potentially, a lot worse. Other forms, triggered by smaller doses of radiation, mostly affect the bone marrow, resulting in internal bleeding, a drop in white blood cells, and anemia. But if a person is exposed to more than 10 grays of radiation, advanced phases can also have gastrointestinal effects, like severe diarrhea, vomiting, or becoming unable to absorb the nutrients in food. And if the exposure was more than 50 grays, the patient could move really quickly through all the earlier stages to reach the manifest illness stage in a matter of hours. And in cases like these, damage occurs to the central nervous and cardiovascular systems, resulting in convulsions or comas. And… there isn't really any chance of survival. But, the good news is, in most of those lower-dose scenarios, a person can recover—especially if they receive prompt treatment. Though, there is no silver bullet. Hollywood seems to think all you have to do to survive a nearby nuclear disaster is pop some iodine tablets. Don't get me wrong, iodine tablets are great. And it's true these pills are recommended as soon radiation exposure is suspected. But they're not a cure-all. In fact, they don't so much treat ARS as prevent the person from absorbing too much radiation in their thyroid—that walnut-sized, H-shaped organ in your neck. See, the thyroid's job is to take iodine and use it to make thyroid hormones, which help regulate your metabolism, among other things. Most of the time, that's totally fine. But if you've been in a fallout zone, you might have radioactive forms of iodine in your body—like iodine 131, which is one of the radioactive elements made in a nuclear reactor. And if a bunch of that gets into your thyroid, it can cause a lot of DNA damage and even lead to thyroid cancer. Iodine pills contain potassium iodide, a stable form of iodine. The hope is that your thyroid absorbs it instead of the radioactive stuff. And for that reason, they do help—but they only really protect the thyroid, because it's the body part that sucks up most of the iodine in your body. And they don't help your body deal with any other radioactive elements. Plus, they don't actually do anything to the radioactive material. And if a person has radioactive stuff inside them—what doctors call internal contamination—getting rid of it will help minimize the total damage done, so that's an important part of treating ARS patients. Radioactive elements do eventually stop emitting radiation on their own, of course. Radioactive iodine, for example, has a half life of about eight days—so even if it's still in a person's body, after 8 days, it's lost half of its radioactivity. But it takes almost two months for it to lose 99% of its radioactivity, and other radioactive elements have much longer half-lives. And remember, they're emitting cell-damaging radiation that whole time. So it's not ideal to just wait things out. That's why, to speed things along, doctors might give a patient substances like radiogardase or DTPA, which bind to radioactive metals to stop them from entering cells and block them from emitting radiation. Once bound, they'll leave the body in urine or feces. Even then, though, the whole process of totally removing radioactive material from a person's body can take several weeks or even years. And it doesn't treat the damage already done. Actual treatments for ARS might include transfusions to replace the blood cells that were damaged or destroyed by radiation, and cytokine therapy to stimulate the bone marrow to make more white blood cells. Many patients are also given antivirals and antifungals to prevent infections while their immune systems are weakened. And hopefully, with enough medical support, the person will reach the final stage: recovery, where things pretty much go back to normal. So yeah, radiation sickness can be really bad, but even without iodine tablets, people can recover. That's different from a lot of what you see in movies or TV shows, where basically anyone exposed to radiation dies—even if they only left the bunker for a minute, or were miles away on a bridge watching the fallout. In fact, actual cases of ARS are really rare. And that's in part because the events that lead up to them, like nuclear bomb blasts or reactor meltdowns, are thankfully rare. But it's also because you have to be pretty close to the action to get ARS. For example, as awful as the Chernobyl accident was, cases of ARS were limited to people who worked in the plant or who went on-scene as emergency responders, and most of them actually didn't get ARS. There were no confirmed cases in the residents of the closest town. Of course, the rareness of ARS is part of why we didn't really know a lot about radiation sickness or how to treat it when some of the most inaccurate movies or shows were filmed. So they really may have thought that people with ARS were emitting tons of radiation, for example, though we now know better. And even today, myths from the past can persist because we don't really see ARS cases in our everyday lives. Also, some things are just a whole lot less entertaining if they're portrayed accurately. Like, we wouldn't have superhero movies if we let reality get in the way of a good origin story. So maybe we can forgive our favorite filmmakers for not getting all the details 100 percent right. Maybe. Of course, science fiction doesn't always get things wrong. And if you liked learning about the scientific realities behind these TV tropes, you might like our episode on 5 Sci-Fi Futures We Actually Should Worry About.