Why are intravenous (IV) drug users at greater risk for skin abscesses, infective endocarditis, and necrotizing fasciitis? a. IV drugs interfere with the normal function of the immune system. b. IV drug users are at increased risk for living in unsanitary environments. c. With each injection, bacteria on the skin are pushed into tissues under the skin. d. The chemicals in IV drugs increase how quickly viruses and bacteria spread..