Hillary Clinton’s health is in the news after she stepped out of a September 11th memorial service early after feeling overheated. The presidential candidate was diagnosed on Friday with pneumonia and put on antibiotics. According to her physician Dr. Lisa Bardack, Clinton is now "recovering nicely."

But that hasn’t stopped conspiracy theories about Clinton’s failing health, continuing from just a week ago when the focus was on her coughing attacks — despite official records stating that, overall, she seems to be doing fine.

After this increased scrutiny over the candidate's health, Clinton's campaign released additional health information on Wednesday afternoon. She had a non-contagious form of bacterial pneumonia that she was treating with antibiotics for 10 days. The blood pressure, heart rate, and cholesterol indicators from her physical were all normal.

But what exactly is Clinton’s so-called "walking pneumonia?" How serious is it, and is it likely that she acted recklessly by being in public when still possibly infectious? To answer these questions, The Verge spoke with Christian Merlo, an associate professor of medicine at the Johns Hopkins University School of Medicine who specializes in pulmonary disease.

What exactly is pneumonia? And how is "walking pneumonia" — this term we’re seeing everywhere — different from regular pneumonia?

Pneumonia is an infection in the lungs, and it can be caused by a variety of different things, from bacteria to the flu virus. When there’s an infection, the body’s reaction is to send the immune system in to attack it. The lungs produce mucus to isolate that infection in there, but in the process the pus gets stuck in the lungs and it fills up part of the airways. Because of that, the lungs, or part of the lungs, will not function properly. Normally, oxygen is brought in through the air tubes. But if they’re blocked with mucus and infection, the oxygen is not going to get in and the body obviously needs oxygen, so it’s a bad situation.

"Walking pneumonia" is a very lay term, and not one that’s really in my vocabulary when I talk to patients. It doesn’t mean some specific type of pneumonia. It’s basically just a milder strain. You can have very severe pneumonia where someone could end up in the hospital, and you could have walking pneumonia where they may not have all the symptoms. They may just have a slight cough, but they may not have a very elevated temperature. They may feel a little bit off and tired, maybe have a loss of appetite. So there are symptoms that something is going on, but it’s not full-blown like the type that can land you in the hospital. It’s the same disease, just not as nearly as serious.

What are some of the symptoms of pneumonia overall? And can we mistake pneumonia for something else?

Absolutely, it can be diagnosed as something else. That’s the key here, that in particular when we care for patients who are older, the symptoms are just very vague and associated with a lot of things. Symptoms of milder pneumonia can be just "feeling bad," loss of appetite, loss of energy, not really feeling like yourself. These are all things that could point to pneumonia but also to a lot of different things. Pneumonia is mostly diagnosed by taking a health history and physical with things like listening to the lungs with a stethoscope, tapping on their lungs.

We know that pneumonia is infectious. Is there a correlation between the severity of pneumonia and how infectious you are? So, is it that the worse your pneumonia is, the more infectious you are?

Pneumonia is spread through inhaling infected airborne particles, so yes, you can catch it when you’re near someone who is sick and coughing and sneezing. I don’t think there’s a direct correlation between severity and how infectious you are. It’s more of a connection with the type of microorganism that infected you.

I read that Clinton’s doctor knew on Friday that she had pneumonia and put her on antibiotics. Yet she was still out and about. Is that normal? It possible she was still infectious at that point?

I don’t know the specifics of the case, but I would say it’s unlikely for her to be infectious at that point because that’s what the antibiotics are for. They’re there to kill bacterial infections and after some period of time — which, again, varies a lot — the infectious risk decreases. That said, I don’t think there’s any way to tell with any specificity how long after someone takes antibiotics they stop being infectious.

But it is normal for people to be able to do things after being treated. It really depends on the severity of it.

Who is most likely to get pneumonia? How serious is it and how common?

The elderly and young are most vulnerable. We don’t know exactly why, but it might be because young people’s immune systems haven’t fully developed yet, and older people’s immune systems are weakening.

There is a wide spectrum of pneumonia. The spectrum ranges from walking pneumonia to being critically ill in the hospital in the intensive care unit, requiring a breathing tube and a machine to help you breathe. I don’t have exact numbers, but it is a common disease and though it can be dangerous, the vast majority of pneumonia cases are not on that side of the spectrum where you’re super sick.

Is it possible to just "wait out" certain strains of walking pneumonia?

It is possible. We have to remember that before antibiotics were invented there were probably very mild cases that people just got over, and even cases of more moderate pneumonia that people got over if they rested a lot.

Another thing I read is that dehydration was a factor in making Clinton leave the service. Dehydration isn’t great at any time, of course, but does it specifically make pneumonia worse?

It’s certainly something that makes pneumonia worse. When someone has an infection in their lungs they oftentimes can have difficulty breathing and feel short of breath, so the reaction to that is to breathe faster.

But as you breathe faster you’re getting rid of more moisture than if you were to breathe normally. In addition, sometimes people don’t have an appetite so they’re not eating and drinking as much. Plus, the body is revved up fighting the infection so it’s using more of its energy. The heart is pumping faster, everything is occurring faster. It’s like when you run in a marathon, your body is using up its nutrients and working harder, so it needs more water and that’s how people can get easily dehydrated and make things worse.