An object is said to be hot if its temperature is more than our body temperature. If we touch such an object, heat flows form it to our body and we sense the difference in temperature. In case the object is hotter, it causes pain and may even burn our skin. Similarly, an object is said to be cold if its temperature is lower than our body temperature. When we touch it, heat flows form our body to the object.
We know that our body is made up of molecules, and these molecules are made up of atoms. At normal body temperature these atoms are in motion, or vibrating. The atoms vibrate slowly when cold but faster when hot. When we touch a hot substance with a fingertip, the fast moving atoms of that hot substance accelerate the motion of the atoms of our fingertip. The molecules at the fingertip suddenly start to vibrate faster, cause pain and a burning sensation. It is the braking up of the molecules that case the burning sensation. To repair the damaged cells, blood circulation becomes faster in the affected area, and it is for this reason that the affected part becomes red.
When the temperature of the object touching the body is very high, a large number of cells and nerves begin to break up. The heat of the substance dehydrates the cells of the skin and they disintegrate. This is called burning.
Sometimes, very hot substances destroy fats and bones. This causes deeper wounds in the body. The scars caused by such burning are removed by grafting the skin taken from other parts of the body.
Burns are classified into four degrees. In first degree burns, only the superficial layers of the skin become red. In second degree burns, deeper layers are damaged and blisters are formed. In third degree burns, all the layers of the skin are destroyed. In fourth degree burns, not only skin but also the tissues beneath it are damaged.
Burns are caused not only by heat but also by chemicals, acids, alkalis, X-rays and radioactive rays.
