For homes infested with fleas, flea bites can be dreadful annoyances that also carry the risk of disease. The flea, a small insect that preys on humans, cats, dogs and other mammals, feed from blood by tearing into the skin. These bites cause small, round marks on the skin that may bleed freely. Due to the tears in the skin, the bites itch, which encourage scratching and further damage to the skin. This can cause a chain reaction, resulting in the flea bites lingering for up to several weeks. For those who are supersensitive to flea bites, the small round, red marks turn into rashes, which can swell and itch even more than a standard bite.