Cold sores have a way of showing up at the worst possible moment. One day your lips feel normal. The next, there’s that unmistakable tingling, tightness, or burning. Within hours, a fluid-filled blister forms. This in-depth guide covers: 17+ science-backed home remedies for cold sores What causes cold sores and what triggers them How to stop a cold sore early Nutritional and immune strategies When to seek medical care