Heat, radiation, electricity or chemicals can cause burns. 

In fact, burn is such a common problem that almost everybody has been burned to a more or less degree in their lives.

Thermal and chemical burns usually occur because heat or chemicals contact part of the body's surface, most often the skin. Thus, the skin usually sustains most of the damage. 

However, severe surface burns may penetrate to deeper body structures, such as fat, muscle, or bone. 

In general, alkali burns are more dangerous than acidic burns because the body could not buffer alkali well. This allows for a much longer duration in injury time.

Injury from electrical burns is mostly internal because the route of least electrical resistance follows nerves, blood vessels and fascia. 

Injury is usually far worse than the external burns at the entrance and exit sites would indicate. Cardiac arrhythmias, myoglobinuria, acidosis and renal failure are common in electrical burns.

When tissues are burned, fluid leaks into them from the blood vessels, causing swelling and pain. In addition, damaged skin and other body surfaces are easily infected because they can no longer act as a barrier against invading organisms.

One to two percent of Chinese citizens (10-20 Million) get burned every year while burns affect 1.4 million Americans annually. 

Approximately 75,000 people are admitted to hospitals annually for the treatment of burns; 10 percent will die as a result of their injuries. 

Older people and young children are particularly vulnerable. 

The seriousness of a burn is measured by how many layers of skin depth the burn goes through and how much surface area the burn affects.