The CDC says it has a growing number of reports about improper use of the injector devices for diabetic patients.
It is sending out a reminder that the devices must never be used on more than one person.
Health officials say using them on more than one person puts people at risk of infection with blood borne pathogens such as hepatitis viruses, and HIV, which causes aids.
The agency warns that infection can occur even if an insulin pen's needle is changed.
Insulin pens are injector devices that contain a reservoir for insulin or insulin cartridge.