eli5: why do mouth numbing gels like orajel numb your mouth and teeth but not hands/skin?


it numbs my tongue instantly but even after 5-10 minutes on skin it feels exactly the same.

In: 57

It absolutely does numb your skin. The active ingredient in Orajel is benzocaine, which is also used in ointments for various other achey body parts, including throat, ears, and skin.

Orajel uses a special formulation that will easily be absorbed by the gums but not the skin. The active material benzocaine is used in different formulations for different purposes, for example sunburn medicine uses it.

Skin has an outer layer of deceased keratinized skin cells tightly bound with each other. They’re pretty waterproof and thus also resist absorption of many other things. Including the benzocaine mix in Orajel.

They technically do absorb it, but very very slowly compared to the mucus membrane tissues of the cheeks, tongue, and gums.

Your skin is thicker and chemically different than your mouth. The orajel can easily soak in and actually do the numbing in your mouth, but not nearly as easily on your skin. I wouldn’t recommend it, but you could place it on a papercut, where it can get into that wound and start numbing.

It actually can be used in the skin, well at least the active ingredient, Benzocaine, can. I just used some a couple of months ago and found out the hard way I’m allergic. My chin is still a bit numb from the experience.