A peer-reviewed survey study published earlier this month in PLOS One found that, for healthcare workers, nose-picking increases covid infection risk, and the risk increases with frequency (go nose mining more, and infection is more likely) (via This Week in Virology).
Nail-biting and other factors didn’t seem to affect risk. But we should note that only 219 people responded to the survey. Researchers also acknowledged that recall bias and “potential shifting of (nose picking) behavior” could influence the results. There was another caveat:
We did not ask whether HCW [healthcare workers] committed to nose picking and nail biting when on the work floor, or the specifics of inter variability between nose pickers, e.g. the depth of penetration and eating of boogers.
