Head lice will feed on any blood type, but some blood types are more attractive than others. Once they begin feeding on a certain type, they need the same blood type to survive. Studies conducted by Terry Meiking, research assistant professor, Department of Dermatology and Cutaneous Surgery at the University of Miami, found that head lice intentionally avoid an incompatible blood type (especially where the Rh factor is different) unless they were starving. When a louse consumes another blood type, its intestinal tract explodes. But if the louse laid nits prior to feeding, those nits are able to feed on the new blood type.