I can. Blowing in a cartridge is bad for it, because your breath contains moisture. The contacts are copper (as are the vast majority of electrical wires), and moisture causes them to oxidize. So, while your breath can clear dust and other particles off of the cartridge's contacts, the moisture in your breath will eventually cause the contacts to corrode. Clean off the contacts with a small cloth, or use an airgun to clear dust off of them. If you have blown on them before and the contacts are corroded, use a small cloth soaked in alcohol to clean the contacts, then dry them afterwards.