No formal diagnostic guidelines exist yet to confirm that someone is suffering from long COVID.

Although the Centers for Disease Control and Prevention is working on a list for doctors, anyone concerned about their health for now has to do their own research and discuss their symptoms with their doctor.

"People could be suffering from long COVID and not knowing it because they have not gotten the knowledge to identify themselves as having it," Fidaa Shaib, a pulmonologist at Baylor College of Medicine's long COVID clinic, told Insider.

Long COVID presents with a huge variety of symptoms, Shaib added, which makes it difficult for doctors to spot.

That is, in part, why estimates of how common long COVID is vary widely. A large UK study found that about one in 10 COVID-19 survivors will develop long COVID – defined as experiencing lingering symptoms for more than three weeks after being infected. A University of Washington estimate, meanwhile, put the figure at closer to one in three COVID-19 patients.

Dr. Ziyad Al-Aly, an epidemiologist and chief of research at a Veterans Affairs teaching hospital in St. Louis, told Insider that the syndrome "can affect nearly every organ in the body."

It is not yet clear if the symptoms of long COVID are caused directly by the virus, or if some are triggered by the stress and trauma of infection and the pandemic. Regardless, people urgently need help managing their symptoms, Shaib said, especially those associated with chronic illness.

Here are 12 ways patients can be affected by long COVID.

Brain fog

One in five long-haulers experienced brain fog six months after having COVID-19, according to an analysis of 51 long COVID studies that has not yet been peer-reviewed. This was the case regardless of whether the patients had been hospitalized or not.

Fatigue

Six out of 10 survivors of COVID-19 who'd been hospitalized reported muscle fatigue and weakness six months later, according to a Chinese study.

Both brain fog and fatigue are hallmarks of chronic fatigue syndrome as well.

Trouble with sleep

One in five long COVID patients reported having trouble sleeping six months after getting sick, according to the analysis of 51 studies.

Shortness of breath and persistent cough

Shortness of breath and persistent cough are common among COVID-19 survivors one to six months after infection, according a study of over 73,000 US veterans.

Heart problems

Palpitations and irregular heartbeat were common among COVID-19 survivors, according to the study of US veterans.

COVID-19 survivors were also at an increased risk of developing heart failure, atherosclerosis, and blood clots within six months after infection.

Myocarditis, an inflammation of the heart muscle, has also been observed in long COVID patients.

Neurological symptoms and mental illness

Over a third of COVID-19 survivors experience neurological symptoms or mental illness within six months of infection, a large study found. Anxiety and mood disorders, such as depression, were the most common.

Loss of smell

Among those who lost their sense of smell after COVID-19, about a third didn't regain the sense for two months or more, according to a small US survey.

Gut symptoms, such as loss of appetite and diarrhea

A small study from China found that more than 40 percent of patients hospitalized with COVID-19 reported issues related to the gut three months after their primary infection. The most common symptoms were loss of appetite, nausea, acid reflux, and diarrhea.

Skin rashes and hair loss

COVID-16 survivors reported skin rashes six months among after infection, according to the study of US veterans.

A study from China documented hair loss among 22 percent of patients six months after hospitalization for COVID-19.

Chest tightness, joint and muscle pain

In a survey on long COVID symptoms published in December, nine out of 10 people reported symptoms like chest tightness, muscle aches, and joint pain one month after infection.

These symptoms persisted for at least seven months for some respondents. The data, however, has not yet been peer-reviewed.

Diabetes

According to the study among US veterans, long COVID patients were 39 percent more likely to get a new diabetes diagnosis in the six months after infection.

Kidney disease

Those who survived COVID-19 were also at higher risk of developing acute kidney disease, according to the study among veterans.

Patients have reported other symptoms that haven't yet been documented in large studies

Long COVID patients have reported a number of other symptoms that scientists haven't been able to measure or confirm yet.

For instance, some women with long COVID have reported irregular periods and worse premenstrual syndrome. Other long COVID patients have said they've had bad tinnitus, a persistent ringing of the ears.

Although some people with long COVID reported that their symptoms got better after vaccination, others said they got worse.

This article was originally published by Business Insider.

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