With proper care, slimes can last for a few months. However, it is normal for slimes to deflate or melt over time due to the nature of slime ingredients. To keep your slime in a good state for as long as possible, make sure to wash your hands before playing and play on a clean surface to avoid debris or bacteria from getting into your slime. After playing, store your slime in an airtight container and a cool environment. Reactivate your slime frequently using slime activator to avoid your slime from melting.