Intense nocturnal itching should raise suspicion of scabies.

Scabies is caused by infestation with a parasitic mite Sarcoptes scabiei var hominis. The itch and rash appear to be largely the result of a delayed (type IV) allergic reaction to the mite, its eggs and excreta. Scabies is spread by a mite transferring to the skin surface of an unaffected person, usually by skin to skin contact with an infested person, but occasionally via contaminated bed linen, clothes or towels.