A potion that caused severe swelling when touched. During one Potions lesson, a stray firework meant that a cauldron of Swelling Solution exploded across the classroom causing melon-sized noses and oversized lips and arms. The students were cured with a dose of Deflating Draught but it was enough of a distraction for Hermione to gather the ingredients she needed for her illicit Polyjuice Potion.