What type of burn requires only cold water for treatment and is the least severe?

First-degree burns are characterized as the least severe type of burn. They affect only the outer layer of skin, known as the epidermis. The primary symptoms of first-degree burns include redness, minor swelling, and pain in the affected area, but they generally do not lead to blisters or severe damage to the underlying tissues.

When treating a first-degree burn, the most effective first aid is to cool the affected area with cool (not cold) water. This helps alleviate pain and reduce inflammation. Cold water, or ice, can potentially cause further damage to the skin, which is why it's recommended to use cool water instead.

Second-degree burns involve both the epidermis and part of the underlying layer of skin, resulting in blisters and more severe pain. Third-degree burns extend through the skin into deeper tissues, often leading to numbness due to nerve destruction, while fourth-degree burns can affect muscle and bone as well. Both second, third, and fourth-degree burns require more advanced medical treatment and care than first-degree burns.