Bed bugs typically feed at night when we are sleeping. Even though these pests commonly feed for 5 minutes, the bite itself is painless and usually goes undetected at the time. In fact, bed bugs inject an anticoagulant (a blood thinner) as they feed, which makes feeding easier for the bed bug and also less detectable to you. Although you may not see the bed bugs, or feel their bites, they know when you are around. Bed bugs are attracted to warmth and carbon dioxide. So, if you are alive, warm, and breathing - then you are broadcasting loudly and clearly to all nearby bed bugs that "dinner is served!"
To reduce the effects of swelling and rashes, you could take an over-the-counter antihistamine, which is usually in the form of an oral pill. Be sure to check the product label for possible side effects, though: some may cause drowsiness, dizziness, irritability, and vision changes, ringing in the ears, and other disrupting symptoms. You’ll want to be careful about taking these pills if you’re going to be driving or operating heavy machinery, and you definitely want to talk to your doctor first if you’re pregnant or have high blood pressure.