Yellow cartoon faces — and occasional brown poop icons — have become everyday forms of communication for many Americans, and now the Mayo Clinic is discovering that emojis can also be used to reliably track patients’ health.

Mayo researchers gave Apple watches and mobile phone apps to 300 cancer patients and asked them to report how they were feeling on a standard zero-to-10 scale but also on a new five-face emoji scale — from really smiley to a big frown.

Early results for the first 115 participants suggest that emojis are just as reliable in providing doctors with meaningful health information.

“We believe this technology has the potential to improve the way we care for patients,” said Dr. Carrie Thompson, a Mayo hematologist who led the study. “In the future, it may be possible to monitor patient symptoms and communicate with patients between appointments via wearable technology.”

The study is hardly the first use of facial expressions to simplify communication with patients. Faces on the common 10-point pain scale make it easier for doctors — especially when working with children or people with limited English language skills — to understand how much their patients are suffering.

But the idea of the Mayo study was to harness the immediacy of mobile devices and emojis and make it easier for patients to report their physical and emotional status. Real-time updates are important when working with cancer patients, Thompson said, because understanding their ups and downs can have an impact on their outcomes.

“Cancer patients receive complex medical care … that may result in physical, emotional, financial and spiritual consequences that can negatively impact quality of life and the ability to perform certain activities without help,” Thompson said. “These quality of life factors play an important role in predicting survival and determining the best treatment.”

Patients in the first week of the study wore the watches for a little more than nine hours per day and took, on average, 3,760 steps per day.

Those who were more active were also more likely to report better emotional and physical well-being on the zero-to-10 scale. Importantly, their emoji responses tracked closely with their numeric responses — suggesting that doctors could cut out complex questionnaires and rely on happy and sad faces to learn how their patients are doing.

“If we can demonstrate that simple emojis are a valid and reliable measure of patient well-being,” Thompson said, “it could revolutionize the way patient well-being assessments are accomplished.”