Why is it dangerous to open a radiator cap while the engine is still hot?

Opening a radiator cap while the engine is still hot is dangerous because the pressurized coolant can erupt and cause severe burns or scalding. As the engine heats up, the pressure inside the cooling system increases significantly, and releasing that pressure suddenly can lead to a violent spray of hot coolant. Additionally, the sudden change in pressure can damage the radiator or other components. It's always best to allow the engine to cool down before attempting to open the radiator cap.