How long do numbing creams lasts and numb the skin?

Topical medications at best work for several hours. The best numbing creams last about 20 minutes or so and numb the skin by interfering with the ability of the nerves to conduct impulses. As such, these creams should NOT be used more frequently than prescribed or permanent effects and damage can be done to the ability of the nerves to properly transmit temperature and pain sensations. Also, all topical medications can have systemic effects.