My roommate has been developing what look like insect bites, but we can find no insects. We have set out sticky traps and have only caught lint. He feels like he is being bitten and then develops wheals with what looks like a bite site. There is no accompanying rash, and the wheals are scattered over his arms, legs, and torso rather than localized as in shingles. He has had chicken pox, but the randomized scattering of the wheals (without rashes). They itch intensely, and he scratches until they bleed. I sleep in a different room and have not experienced any bites, even though he has been being bitten for over a month. We have checked his bedding and mattress, but have not found any signs of insect infestation. What could be causing this problem?