When people become gravely ill from COVID-19, a cytokine storm — their body’s own reaction to the virus — may sometimes make things worse.

The phenomenon has been described as “an immune system gone wild,” harming the patient while going after the virus and increasing the severity of symptoms.

With COVID-19, this “overly exaggerated response” focuses on the lungs first, said Dr. Randy Cron, a professor of pediatrics and medicine at the University of Alabama at Birmingham, who is an expert on the phenomenon.

“It can be very bad. It’s contributing to a significant number of deaths in this outbreak, unfortunately,” Cron, co-author of the textbook “Cytokine Storm Syndrome,” told TODAY.

“The human race has not seen this particular virus before… (but) every single day in intensive care units across the planet, there are people dying of cytokine storms, many of which go unrecognized and therefore untreated.”

Many conditions, including cancer, autoimmune diseases and infections, can trigger a cytokine storm. Since the coronavirus is so new, doctors and families of patients dying from COVID-19 have been contacting Cron for his advice about how to stop the unwanted immune response. He’s lost 30 pounds from the stress, he said.

Here’s what to know about the phenomenon:

What is a cytokine?

Cron described it as a hormone of the immune system. The body produces cytokines to help fight bacteria, viruses and other invading organisms.

These proteins can have pro-inflammatory features to attract white blood cells to the site of an infection. There are also anti-inflammatory cytokines to try to ramp down an immune response.

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What is a cytokine storm?

It happens when the pro-inflammatory cytokines get out of control in abundance. Normally, if you get sick, your immune system mounts a response to clear the infection and then shuts itself down. But that’s not happening in this case.

“It’s not from having a super good immune system. It’s from having a subtle defect in the ability of the immune system to do its job,” Cron said.

“It gets overly activated and that exuberance of these pro-inflammatory cytokines is what leads to multi-organ failure and potentially death,” Cron said.

The phenomenon can strike people of all ages, including children.

When it comes to COVID-19, recent research has suggested about 20% of people get the severe form of the disease. Many in this group become critically ill because of their advanced age or underlying health conditions. But those who were previously healthy and are in their 30s, 40s, 50s are very likely experiencing a cytokine storm, he noted.

What triggers a cytokine storm?

More than 100 different organisms — mostly viruses, including the new coronavirus — can trigger a storm. They include certain strains of influenza like H1N1 in 2009, hemorrhagic fever viruses like dengue fever and herpes viruses like Epstein-Barr, Cron said.

But not all people are affected, even if they get the same bug. About 10-20% of the general population may have a genetic risk factor that gives them the subtle defect in their immune response that puts them at risk for a cytokine storm with certain infections, he noted.

How is a cytokine storm detected?

It can be diagnosed by measuring serum ferritin in the blood, a non-specific marker of inflammation.

What happens to the body during a cytokine storm?

The liver often becomes damaged and people may experience bleeding and clotting abnormalities.

Patients experiencing a cytokine storm tend to be sicker overall than others who have the same infection. In the case of COVID-19, they may have respiratory distress — not just coughing, but trouble oxygenating.

The cytokine storm caused by the new coronavirus seems to have some subtle differences, “the primary one is that it really focuses on the lungs first, whereas in other cytokine storms, the lung tends to be a later finding,” Cron said. Acute respiratory distress syndrome is a major problem for patients with the severe type of the disease.

The mortality rate can range from 40-80% in adults for other cytokine storms.

Can a cytokine storm be treated?

Yes. Drugs have been given to stop cytokine storms caused by other conditions.

“People can survive it. If you treat it early enough and sometimes even late, you can get through it all,” Cron said. “For other cytokine storms, you can essentially come out of it unscathed.”

When it comes to COVID-19, clinical trials are under way to find out what truly works to treat a storm, he noted.