Contamination at the site of the donor's skin may occur despite proper disinfection, because pathogens in deeper regions (such as pores) may not be eliminated by skin disinfection. It is suspected that the cannula detaches fragments of tissue when it penetrates the skin; the tissue fragments may reach blood products and release pathogens there. In the present study we punctured piglet skin with cannulas commonly used for blood donation and performed histological as well as cytological investigations of the lavage fluid in the cannula to identify superficial skin cells and skin plugs. Histological specimens of the pierced skin showed frayed puncture sites with loosely attached tissue fragments. In the lavage fluid of the cannula, a collection of epidermal cells was found in one of 150 punctures. Our results confirm that the phlebotomy cannula may cause superficial tissue fragments to be punched out of the donor's skin during blood donation. This fact should be taken into account when devising methods to reduce bacterial contamination in blood products.