Hiranyakush had a sister, Holika. She had received a boon from Vishnu that she could bathe in fire and was never to die of wood or fire. The only condition was she must never touch a man. Now Holika was very fond of baby Prahlad. So she picked up the little boy and put him on her lap. As soon as her skin touched him, she fell dead and Prahlad walked away.
The same image is used to tell the story of Krishna and Pootana by some tellers.