By now, most people have seen friends or celebrities pour buckets of ice water over their heads as part of the “ice bucket challenge” for amyotrophic lateral sclerosis, the neurodegenerative condition also known as Lou Gehrig's disease.

This behavior has gone viral and taken over Facebook to an extent rarely achieved by health-care topics. Reflecting on why is important, because health systems working on topics ranging from colorectal screening to vaccinations have much to learn from this campaign.

The challenge entails pouring a bucket of ice water over your head while someone takes a video. You call out three friends to do the same within 24 hours or donate $100 (or both), and then post the video on social media. In weeks, millions have become engaged in the challenge while developing an awareness of ALS. The ALS Association reports a ten-fold increase in year-over-year donations. Great success, but what explains it?

Jonah Berger's book “Contagious: Why Things Catch On” and leading companies studying word of mouth offer some perspective on why certain ideas spread and lead to action.

People don't tell stories to friends and family about everyday experiences. You won't hear, for example, “You have to try this app. It really met my expectations.” The stories that are told and retold have a punch line or surprise. The unexpected is what makes it a good story. On some level, we all know this, but we often don't design our campaigns to fit that model.

Imagine meeting with your colleagues from the ALS Association, and you're tasked with increasing awareness and donations. You might consider various marketing campaigns (Could we create our own “Race for the Cure”?), debate wording (Should we describe the disease as “vicious” or “incurable”?), or think about the ideal spokesperson. But can you imagine suggesting, “Hey, we should each pour a bucket of ice water over our heads and challenge our friends to do the same!”

When teams generate solutions to a defined problem, priorities rarely incorporate surprises or venture into the realm of what the target audience would not expect. We're socialized to propose logical directions based on why a problem is happening. Ideas that might be labeled “surprising” can't easily compete with expected attributes, and even suggesting them can feel risky to your reputation. Yet it's the unexpected that drives people to spread the word, be it exceptional service (“Zappos just gave me free overnight shipping without my asking!”) or product performance (“I held my phone up to the radio and Shazam told me what song was playing!”).

In “Contagious,” Berger points out that when something is remarkable — as in truly worthy of remark — the person sharing that information gains social currency. Being in possession of such content confers status, which promotes spreading the word.

When the founder of Blendtec made videos showing his blender pulverizing everything from a wooden rake handle to an iPhone, they were indeed amazing. Seeing an iPhone turned to dust brought to life the blender's distinctive benefit with an unexpected delivery. It's no wonder that these videos were frequently shared, boosting sales 700 percent.

Watching friends dump buckets of ice water on their heads is certainly surprising, and sharing yields some social currency. Yet the design delivers status even more directly. The script has participants explicitly name three or so people they're challenging to join the movement. Being chosen publicly states that you are important and close to the challenger. The list is short enough that those selected feel special and elevated in status. And people who accept the challenge start by thanking the person who chose them, emphasizing the honor of being part of the club.

Far from random luck, the challenge is an exemplar of design for viral spread.

Health-care organizations rarely consider the power of social ties to influence a target audience. Privacy concerns and regulations arouse conservatism and limited engagement strategies. The ice bucket challenge invites us to consider new ways to advance social good with elements of surprise, social currency, and making normally private actions public. By heeding these principles, health-care organizations may find themselves in the ALS Association's enviable position of seeing ideas serving their interests continually amplified and acted upon.

Roy Rosin is chief innovation officer at Penn Medicine. David Asch is the executive director of the Penn Medicine Center for Health Care Innovation. Raina Merchant is the director of the Penn Social Media and Health Innovation Lab. They wrote this for the Philadelphia Inquirer.