After contracting chickenpox in childhood, the varicella-zoster virus (VZV) remains dormant in the root areas of nerves. When the body’s immune system weakens, the dormant virus reactivates, causing pain in the affected skin area. Since there are no rashes at this stage, it can be mistaken for other diseases.

A few days after the pain begins, redness and fluid-filled blisters appear on the skin. At this point, if someone who has never had chickenpox comes into contact with the affected area, they can contract chickenpox from the rash.