Open flame and hot liquid are most common causes. Tissue injury caused by chemicals or radiation, including sunlight. Lighting strikes can cause internal burns with minimal external signs. Pain resolves in 48 - 72 hours. 2nd degree burns affect deeper skin layers.
Symptoms are more severe and usually include blisters.
Heals within 10 - 14 days. 3rd degree burns involve all skin layers. Cannot heal spontaneously. Occupations involving exposure to heat or radiation, such as fire fighting, police work or defense-factory work. Hot water heaters set too high.