As scores lay injured in Florida hospitals after the Orlando shooting, potential donors inundated blood banks, offering what they could. For some, however, the hourslong wait ended in disappointment. The U.S. Food and Drug Administration has strict guidelines about who can donate blood; among those restricted are people who have had certain diseases, those who have traveled to certain countries and men who have slept with men, or as the FDA refers to them, MSM, within the past year.