Bed bugs feed on the blood of human beings (aka. "blood meal") but can suck blood from other animals as well. Birds and mice are the most common animals. Bed bugs most often feed at nighttime when people are asleep. When they feed, they inject a salivary secretion into the wound to prevent coagulation. The fluid can cause a person’s skin to itch and even become swollen. Scratching can cause sores which often become infected. Bed bugs aren’t known to transmit disease. And some people don’t even get marks when bit. But scratching bites can lead to a secondary infection. Resist the urge to scratch. People with health problems and children are more at risk for infection because their immune systems are compromised or they can’t stop scratching.