The primary way you can get head lice is when your head comes in direct contact with the head of an infested individual. Head-to-head contact like that doesn’t guarantee that the infestation will spread, but it gives lice the best opportunity to move from the hair of the infested person to your hair.
Head lice don’t jump, swim or fly. Without strands of hair to grab with the claws on their legs, they have trouble getting around at all. However, they can crawl pretty quickly along the hair, so if your hair comes in contact with an infested head, it doesn’t take much for a louse to hitch a ride on a strand of your hair and make its way to your scalp.