Since the war in Ukraine began, more than 3 million refugees have fled -- by bus, train, car and foot -- for neighboring countries. Some have destinations in mind, while others have no plan. But as these displaced citizens navigate different yet equally impossible conditions, doctors at the countries that border Ukraine say there's a common thread: mental health is the most often reported medical problem.
ABC News interviewed doctors from the U.S. and Europe who flew to the border to volunteer. According to those doctors, among the millions of refugees, acute stress disorder has been reported as a common ailment.
"Acute stress disorder is basically a fight-or-flight reaction that lasts a few days to a month and involves having been exposed to a threat to your life or limb and not being able to stop thinking about it," Dr. Craig Katz, a clinical professor of psychiatry, medical education, system design and global health at the Icahn School of Medicine at Mount Sinai, told ABC News.
In cases where people are in a fight-or-flight mode, "They're highly likely to have problems sleeping, being extremely anxious and not having much of an appetite, because they need to focus on survival," Katz said.
Russia launched its full invasion of Ukraine on Feb. 24, exposing its citizens to death and destruction, as well as disruption to basic needs.
"It's clearly a nation under stress," Dr. Dan Schnorr, an emergency medicine physician with Doctors Without Borders, told ABC News. "Every child in [Ukraine] is now experiencing multiple adverse childhood events, and that is one of the uncounted casualties that will ripple throughout generations."
“This is a true humanitarian crisis. People are leaving with only what they can carry. Families are being separated. Trying to find a way to make it,” says Dr. Preethi Pirlamarla, cardiologist and director of heart failure at Mount Sinai, Queens.
Research suggests that firsthand exposure to traumatic events, such as the Ukraine war, can have lasting effects, including PTSD, anxiety, depression and relapse of alcohol abuse. According to the American Psychiatric Association, prevalence of acute stress disorder ranges from 13%-50% depending on the type of event exposed to and about half of those individuals with acute stress disorder develop PTSD.
According to Katz, the risk of developing lasting effects of acute stress disorder increases depending on the extent of exposure to a traumatic event, prior trauma that was not well addressed previously, a history of psychiatric disorders and not having social support.
Alternatively, being spiritual, having social support, realistic optimism, being cognitively flexible and having a sense of purpose can all help to mitigate the effects of the acute stress.
"Psychological first aid is a way to attend to people's mental health scratches and bruises so that they don't become festering wounds," Katz said. "You make sure people feel safe and secure, make sure they have meals to eat, you especially make sure they -- as much as you can -- they are together with loved ones or have some sort of communication that has support."
At Palanca, the border crossing in Moldova, psychosocial clinics have been established to identify those struggling mentally and ease the effects of this trauma.
"It's more about listening and giving a shoulder to cry on," Dr. Axel Adolfo, an emergency medicine physician working with Doctors Without Borders, said. "It's about having someone waiting there for them with arms fully open ... They just want to let go of the two to three weeks they spent in fear or doubt and can feel that they are close to [safety]."
The challenge now becomes helping to integrate these populations into neighboring societies.
"People always say mental health is a good idea, but they need to start planning from now," Katz said.
Refugees are at risk of forming lasting mental health effects. Eventually, according to Katz, screening will be important to identify who may need to be connected to a psychiatrist.
For now, though, "It's about being here and saying, 'The whole world is watching, and we are here to help you, and it's OK to cry," Adolfo said.
Nicholas P. Kondoleon, M.D., is an internal medicine resident at Cleveland Clinic and a contributor to the ABC News Medical Unit.