Chickenpox is caused by the varicella zoster virus and causes a blistering rash. It is highly contagious and spreads through the air via respiratory droplets from infected individuals. The rash starts as small red bumps that fill with fluid and scab over in about 7-10 days. While most cases resolve without complications, some can lead to bacterial infections, pneumonia, or encephalitis. Treatment focuses on reducing symptoms with antiviral medications, antihistamines, and fever reducers. The chickenpox vaccine provides protection for most who receive it.