Lidocaine is the main ingredient of most of the numbing creams available in the market. But how does it block the pain on the skin?
The simple answer is that the lidocaine act directly on the nerve cell and prevent the electrical impulses from passing along the nerve. The more complicated answer depends on understanding how the nerve impulse is generated in the first place, which occupies several pages of the textbook. Briefly, in the resting state the nerve cell generates a voltage across the cell membrane by virtue of an active pumping mechanism which pumps sodium ions out of the cell, and allows potassium to diffuse in, to create an electrochemical gradient. When the nerve is stimulated, sodium channels open and allow sodium ions to flow back in, reversing the electrical gradient (“depolarisation”). This electrical change serves to open the sodium channels in the adjacent section of membrane, and so a wave of depolarisation travels along the nerve cell. The local anaesthetic drug works by sitting on the sodium channel and preventing depolarisation, thus preventing the sodium entry into the cell.
In the simplest answer: the lidocaine in the numbing cream blocks the pain by preventing the nerve cells to pass along the electrical impulses which transmits the feeling of pain from the skin to the brain.