The skin doesn’t absorb large molecules easily, which meant Sawicka had to find another way to get vaccines across that barrier. As an undergraduate at Stony Brook University, she worked in a lab that stocked an extremely water-absorbent material called poly-vinylpyrrolidone. She found that this polymer (used in hairspray during the era of beehive hairdos) could pull water out of the skin. When moisture returned, the outer layer of the skin swelled, allowing larger-than-usual molecules to enter.