system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why do we feel the urge to chew/pick at/mess with sores in our mouth, even though we know doing so will make it worse?

Is there a scientific reason we do this? My brain logically tells me that I should bite at the sore in my mouth, etc... but my body feels the urge to mess with it even though it only worsens the problem. ELI5 why this happens?
gpt
Great question! Two important mechanisms: innervation and gate control theory.

First, innervation. What's very different from the inside of the mouth and the tongue compared to skin elsewhere in the body (except the fingertips), is that its greatly sensorily innervated! This means it is much more sensitive to physical stimuli. So abnormal sensations, like aphthae, that occur in the buccal mucosa or on the tongue, are brought to awareness much more than stimuli elsewhere. When something is continuously within awareness, it stimulates a response. Which will be you to touch/press on the painful/uncomfortable area.

Have you heard of the *sensory cortical homunculus*? It's a cartoon that depicts the size of the brain areas involved in the sensory innervation of different body parts. You should see how big the lips and tongue are on the sensory homunculus, compared to the rest of the body. Google it (not the motor homunculus!). 

Secondly, the gate control theory of pain. There are different sensory inputs that are each processed slightly differently on neurological level: pain, soft touch, rough touch, temperature and proprioception. What this theory basically asserts is that when there is pain in a specific area of the body, applying non-painful stimuli (e.g. soft or rough touch) to the same body part closes the "gates" to painful inputs. Thus, non-painful stimuli can alleviate pain slightly by suppressing its neural conduction! This is also the reason why people are quick to put there hands on painful areas (e.g. hand on forehead when having a headache).