I don't think it's alcohol that melts the tubes. I clean mine with isopropyl all the time and no deterioration. What I found is anything with malic acid as zoiDman mentioned, like sour/green apple. Also anything with oil in it like cinnamon (VB's Cinnabomb and Fire & Ice), Sassafrass, and Wintergreen flavors. They turn a rigid plastic to a soft pliable material (it exacerbates already present micro cracks).