MINNEAPOLIS — Debra Safyre was standing in line waiting to order lunch when she was hit by a sudden wave of anxiety.

“There was no reason for me to be triggered that way,” she said. “Then I noticed the person in front of me. She was jittering so badly, shaking so badly, that I was responding to her stress — and I didn’t even talk to her.”

Her experience was not unusual.

Secondhand stress — tension that we pick up from the people and activities around us — is a natural defense mechanism that helped keep our ancestors alive, said Dr. Amit Sood, an expert on stress at the Mayo Clinic. But as soon as we pick up that tension, we risk becoming carriers, passing it on to any friends, family members or co-workers — and, yes, even strangers — who we encounter.

“Stress travels in social networks,” he said. “It is highly, highly contagious.”

Fortunately for Safyre, a former nurse, she quickly realized where her surprise anxiety was coming from and was able to move away from its source.

“It’s kind of like a tuning fork,” she said of secondary tension. “When you hit a tuning fork, everything around it starts vibrating with it. It’s the same thing with stress. If stress is a very strong vibration around you, you’re going to start reacting to it.”

The impact that secondhand stress has on us has only recently been appreciated by psychologists, said Dr. Berendina Numan, co-founder of the Center for Counseling and Stress Management, with offices in Minneapolis and Minnetonka, Minn.

“It’s been only the last 10 years” the topic has been explored in much depth, she said.

Doctors do know that stress in small doses is essentially a good thing, Sood said. It’s part of the body’s warning system that creates the fight-or-flight response and generates a surge of energy that helps us deal with a crisis. But excessive or prolonged stress can lead to health issues ranging from headaches to heart problems.

Protecting oneself from secondhand stress begins with identifying its causes, said Dana Kadue, owner of Life Flow Coaching in Minneapolis.

“The first step is awareness of the things around me that create stress in my life,” said Kadue. “It’s all about self-awareness, discovering when the stress shows up.”

Start the investigation with who’s around at the time, suggested Sood.

Once you’ve identified the problem people, you have three basic courses of action: You can change them. You can get away from them. Or you can learn to protect yourself from them.