Long COVID continues to boggle the minds of the medical community as scientists and medical professionals work hard to uncover what's really causing the mysterious condition. With the large number of people suffering from the illness and unable to return to their normal lives, it's hard to turn a blind eye to the complex condition.

As of late, there are four theories on what could be causing the lingering symptoms long after an acute SARS-CoV-2 infection. All of them seem to explain a group of symptoms associated with the condition; they also have some scientific evidence to support them, according to WIRED. So it's hard to choose one over the other.

The following are the four theories explaining what could be triggering long COVID:

Autoimmunity - A study published last year examined the different factors related to post-acute COVID-19 sequelae. The research team found that long COVID could be caused by the immune system attacking the body during recovery from COVID-19.

Viral Remnants - A different research effort determined that splinters of the virus could be persistently circulating in the body long after the initial infection, causing the lingering symptoms to show since the immune system is revved up to the point of exhaustion.

Organ Damage - There is also a theory that SARS-CoV-2 causes lingering symptoms after damaging certain organs and tissues. In one study, scientists found impaired functioning in the brains of those with lingering neurological symptoms.

Reawakened Viruses - The fourth theory maintains that the body develops long COVID when a SARS-CoV-2 infection reawakens latent viruses people have encountered before. By this theory, experts proposed that chronic viral infections from Epstein-Barr virus (EBV), Cytomegalovirus (CMV) and human immunodeficiency virus (HIV) could be potential contributors to the mystery condition.

WIRED noted that the theories are not mutually exclusive. Some people could have two causes going on; others could have all four happening all at once. That's why it's so difficult to deal with COVID and its diverse symptoms.

A study published in The Lancet examined and listed all of the possible symptoms associated with long COVID. The team found a total of 203 long COVID symptoms affecting 10 organ systems.

Charlie McCone is one of the over 65 million people struggling with lingering symptoms. In an interview with The Atlantic, he shared that life has never been the same since he first got infected in March 2020.

Three years later, he is mostly stuck on his couch or in his bed. He is unable to stand for more than 10 minutes without losing his breath, feeling fatigued and experiencing other symptoms. He said he can only "appear completely fine for two hours a day." He uses this time to attend medical appointments and work in front of his computer for an hour a day.

To help McCone and the many others affected by long COVID, scientists are working hard to come up with treatments that could alleviate as many symptoms as possible based on the four theories. But considering the complexity of the four possible causes, designing clinical trials could be much trickier. Hence, scientists may need more time in finding a solution to the long COVID problem.

The coronavirus disease (COVID-19) outbreak in Hong Kong Reuters / LAM YIK