My friend got second degree skin burns. Why is that?

Injury to skin. 2nd degree burns usually extend into the dermis which can result in scarring depending on how deep the burn is. Usually involves blistering. Caused by heat, chemicals, electricity, fire, light, radiation, friction, trauma. May take several weeks to heal. Need proper wound care, dressings, possibly antibiotics to prevent infection.
Multiple causes. A burn is a type of injury to flesh caused by heat, electricity, chemicals, light, radiation, or friction. First degree burns damage only the surface of the skin; second degree burns damage deeper tissues, and third degree burns destroy very deep tissues and nerves.