Liquid L Carnitine Core Nutritionals L Carnitine Liquid 3000 Metabolic Support What Cold Sores And Fever Blisters Reveal About Your Immune System Cold sores and fever blisters aren't just surface level nuisances; they're signs your immune system is struggling. When these blisters appear and Cold sore triggers vary from person to person, but HSV is an opportunistic infection. That means it rears its ugly head when, for whatever reason, your immune system is too weak to