Bed bugs have an elongated beak with mouthparts that saw through their victim’s skin and insert two hollow tubes. One of the tubes is used to suck their victim’s blood while the other tube injects saliva, which contains anticoagulatns and pain killers.
Because of the injected saliva you normally will not even feel a bed bug biting you, however the saliva is the reason that your bed bug bites itch so bad. Your body naturally is allergic to the bed bug saliva and causes intense itching. The more exposure to bed bug bites the worse the bed bug symptoms get.