After years of too little attention, the subject of head injuries in sports, and how to prevent them, is now what Twitter would call a "trending topic." 

First came the turnaround in attitudes toward NFL player head injuries, and the helmet-to-helmet tackles and hits that increase the risk of those injuries. Then came the discussion about skier Lindsey Vonn's continued participation in the World Cup last week, despite clear indications and admissions on her part that she was still skiing behind the course and "in a fog" after suffering a concussion in a training accident. And now, there's the U.S. lacrosse league debating whether or not the girls -- who now only have to wear protective eye gear—should be required to wear helmets as well.

Girls' lacrosse has dramatically different rules than the boys' game: body checks are illegal, as are certain stick checks, and there is a regulated safety zone around each girl's head. Nevertheless, research quoted in a New York Times article today concluded that when it comes to concussions, lacrosse ranks third in female sports (behind basketball and soccer). In addition, despite the less-aggressive nature and rules of the girls' game, girls' lacrosse has an in-game concussion rate only 15 percent lower than the boys.

So if concussions are an issue in girls' lacrosse, the argument goes, we should require girls to wear more protective headgear. After all, the boys' helmets, intended to reduce skull fracture and intracranial bleeding, are thought to reduce the number of concussions, as well. 

But does the addition of extra safety gear actually reduce the risk of the injuries it is designed to prevent? Well, yes ... and no. Which is what fuels the debate on the issue. 

Taken by itself, it's easy enough to prove that wearing a helmet, like wearing a seat belt, decreases the chance or severity of injury in an impact. But humans are far more complex creatures than crash test dummies. And so the true impact of safety equipment becomes far more complex, as well. 

In his 1995 book Risk, British researcher John Adams spelled out several reasons why safety equipment does not always increase safety the way its designers or legislators think it will. The first is a phenomenon called "risk compensation," in which humans respond to additional safety equipment by taking greater risks than they did when they felt less protected. For example, Adams said, while seat belts unquestionably gave a person better protection if they were in a collision, the chances of being in a collision went up in places with seat belt laws, because seat-belted drivers took more risks in how they drove. 

For all the time and discussion space we devote to the goal of eliminating accidents or injuries, Adams suggests that people have "risk thermostats," and that we all adjust our behavior to maintain the level of risk in our lives that we find acceptable. We all compensate for the extra margin provided by safety equipment to some degree, and some of us will push the new boundaries further than others. All of which means that safety equipment often doesn't make as much of a difference as its proponents believe it will.

Indeed, there are many who argue that mandatory helmets, and increasingly strong helmets, have actually exacerbated the problem of head injury in sports ranging from boys' lacrosse and ice hockey to professional football. So perhaps helmets for female lacrosse players really are a bad idea, as U.S. Lacrosse (the sport's governing body) argues. 

So what's the solution? In many cases, improving safety has had more to do with changing a group's culture and attitudes about high-risk activities than it does any specific technological advance -- especially in individual sports or hobbies.

A prominent example is the Cirrus Design company (a company profiled by James Fallows in his Atlantic article and subsequent book Free Flight). In an effort to build a safer aircraft, Cirrus included a full-airplane parachute and vastly improved "glass" cockpit displays in its Cirrus airplane. But when the airplane was first introduced, it actually had a significantly higher-than-average fatality rate, because pilots -- comforted by the extra technology and safety systems -- "compensated" by pushing the aircraft into weather they wouldn't otherwise have undertaken. In the end, the company was able to bring its accident rates down by requiring additional training and working to change the culture of its buyers—at least to some degree.

The field of SCUBA diving also vastly reduced its accident rate over several decades by changing its group attitudes toward risk. Once upon a time, diving was a macho sport where the toughest regularly pushed the limits. Today, attitudes about pushing the limits have changed. Dive without a buddy, push your depth or time limits, and a diver today is likely to be seen as stupid, not brave. 

Notably, the NFL is now taking a similar approach toward head injuries. Instead of simply improving the cushioning in players' helmets, the NFL is trying to change the league's culture, rules and consequences related to hits to the head, or tackles "leading" with a player's helmet. How well that works remains to be seen, of course. But the popular image and standard for what's "admirable" and "acceptable" in tackling technique has already changed dramatically, even in the breathtakingly short span of a single season. 

But girls' lacrosse already has a restrictive set of rules regarding contact. And most of the concussions its players suffer come from accidental contact and falls, not intentionally aggressive maneuvering. So is it a different case? Could helmets actually make it safer?  

"I think helmets encourage you to push the limits of whatever the rules are," one high school athlete responded, when I asked the question. "If you're only allowed one kind of hit, you'll hit as hard as you can in that one way. But given that girls' lacrosse has so many rules restricting contact, [helmets] might actually help." 

Of course, given the complexities of how humans assess and respond to risk, and the fact that lacrosse players are unlikely to be timid or risk-adverse by nature, it's also a fair bet that whatever safety margin helmets provide would—at best—be narrowed by some amount by compensating behavior on the part of the players. Which means at some point in the future, U.S. Lacrosse, like Cirrus and the NFL, may find itself compensating for that compensation through more complex solutions than the seemingly-simple answer of a helmet.