**Dense fog** is dangerous when driving because it **reduces visibility**. This means it is more difficult to see the road, signs, and other vehicles. For this reason, it is important to take additional precautions, such as turning on the **dipped headlights and fog lights** to improve visibility. Additionally, it is recommended to drive slowly and maintain a considerable safe distance from other vehicles.

Fog can also make the ground wet, which **reduces the grip of the tires** on the road, increasing the risk of skidding. Therefore, it is crucial to pay attention to road conditions and avoid sudden maneuvers.

In summary, dense fog **reduces visibility**, making it necessary to take precautionary measures to drive safely.