Visual hostility is hardly confined to the schoolyard.

Machiavellians, sociopaths and bullies of all ages are known to commit random acts of eye violence, for no other reason except that they can. They flash over-the-top visual aggression at times when to do so is simply gratuitous. A death look at a driver who comes too close, a cut-eye at someone who gets in the way, a hate glare at “one of them.”

Even the most seemingly pacific of people, who might otherwise draw the line at overt expressions of physical or verbal violence, will flash eyes of judgment and careless contempt at people around them. Women and men, old and young, of every color, who indulge in casually vicious looks, rationalize, “She deserved it.” “He was in my way.” “I felt like it.”

And why not? If there’s no actual contact, no damage done, right? Hate eyes are safe, even socially sanctioned, methods of being malicious. Simple to excuse if they’re even noticed at all, and easy to hide, eye aggressions appear harmless.

Research into the consequences of relational violence doesn’t support this perspective. Studies, and a great deal of anecdotal evidence, shows that exposure to aggression does have a measurable negative impact on psychological well-being. And it’s not just the thin-skinned who are affected. A hostile look from the right person, at the right time, can induce tension and self-doubt in the most resilient of individuals. Both in the moment and afterwards, eye violence can cut to the emotional quick, blocking and paralyzing.

The effects are physical too. Exposure to hostile eyes arouses, sending cortisol and adrenalin levels soaring. Repeated exposure prolongs sympathetic nervous system activation and fight or flight responses. Over time, one’s reserves of energy and attention deplete, weakening the body and rendering it more vulnerable to illness.

There are consequences for the perpetrator too. Although impact statements tend to focus on victims of visual violence, research shows that expressions of aggression can be costly to offender. Studies show that “Cynical Hostility”, characterized by enduring negative interpersonal attitudes and behaviors, including antagonistic eye expressions, is a risk factor for adverse health outcomes as diverse as cardiovascular disease and post-traumatic stress disorder (PTSD).

While the cause and effect is not yet clear, experts speculate that expressions of hostility stimulate cytokine levels in the body. Central to immune system functioning, cytokine activation negatively impacts on mood, accelerates processes of aging and manifest in a myriad of symptoms. In short: Intentional expressions of animosity, visual or otherwise, are toxic to the sender at a cellular level.

Worth thinking about next time you feel like sending someone an evil eye.