WASHINGTON – Scientists may have unraveled one of the great medical mysteries of all time: who gets the common cold and why.

Researchers studied 152 volunteers between the ages of 18 and 55. Via nose drops, researchers gave the healthy volunteers the virus for the common cold — and paid them $1,000 each, NBC News reports.

Once the patients became sick, their telomeres — structures within immune cells that NBC says cap chromosomes like the tip of a shoelace — were compared to the telomeres from when they were healthy.

White blood cells with shorter telomeres don’t protect as well against infections and sickness, scientists tell NBC. In the study, those with the shortest telomeres got sick more often than those with the longest.

Read more about the study from NBC News.

WTOP’s Del Walters contributed to this report. Follow @WTOP on Twitter.