Every year, many people get sick with the flu. Most of them find it miserable, then recover. But every year, some people die from it.

How exactly does that happen? What are the factors that can cause the flu to kill you? According to Popular Science, there are a few ways the flu can do you in.

1. Age

It’s especially risky when babies or elderly people come down with the flu. Babies and toddlers haven’t been exposed to enough pathogens yet, so their bodies aren’t well-versed in how to fend off a viral infection. The elderly tend to have declining immune systems, because that’s what happens when you age.

Of course, people who are not especially old or especially young can still die from the flu, especially if it’s a strain of flu they haven’t been exposed to before. But babies and elderly individuals are more likely to experience deadly cases of the flu.

2. Secondary infections

Our bodies are home to many strains of bacteria all the time. Most of them are harmless and do us no harm when we’re in good health. But when your immune system is bogged down with fighting off a nasty case of flu, previously harmless bacteria can seize the opportunity to spread, often to your lungs. That’s how a person with the flu can end up with pneumonia. And pneumonia can kill you.

The good news is that there’s a way to combat this potentially deadly secondary infection: Go to the doctor. If you’ve taken a turn for the worse, don’t wait it out, go get checked out. Doctors can give you some antibiotics, and maybe some oxygen. Pneumonia is no joke.

3. Lung inflammation

About one-third of people who die from the flu die directly from the flu, rather than from secondary infections or complications. Respiratory failure occurs when your lungs are unable to get enough oxygen, and it’s one of the most common ways to die from the flu. Unfortunately, lung inflammation can occur very quickly and without much warning.

Inflammation is a sign of healing. It means there are new cells attempting to heal your body, and organs swell in order to make space for them. However, sometimes when this happens in your lungs, the swelling can prevent oxygen from being able to reach your blood vessels. That’s one of the ways that lung inflammation can occur as a result of the flu.

4. Inflammation of the heart or brain

You can damage your liver and still go about your life to some extent. Same goes for your kidneys. But your heart and brain are essential to keeping you alive, and must function properly in order to do so. This means damage to either organ can kill you swiftly.

If your flu infection causes swelling in these organs, that’s a huge problem.

5. Multiple organ failure

Obviously multiple organ failure is not what you want. Another word for it is “sepsis,” which sounds equally scary. Sepsis is what occurs when your immune system reacts really strongly to the bug it’s fighting off, causing all your organs to swell. This inflammation overwhelms your body, and your organs can all shut down as a result. From there, it’s very quick.

The good news is that most people do not die from the flu. It’s scary, of course, but getting the flu shot is proven to reduce the severity of your illness, even if it doesn’t prevent you from getting the illness in the first place (though it does reduce your risk). The other thing to remember is that your immune system functions best when you care for it properly, so if you’re sick, drink plenty of fluids, get some real rest, and go to the doctor if something feels like it’s just not right. It’s your body, and it’s better to be safe than sorry.