Could someone who is shy and over sensitive be an indicator of low dopamine? Or not really? Or perhaps another neurotransmitter?
There are several neurotransmitter deficiencies that are believed to play a role in shyness. Dopamine does appear to be the primary one, although there is some evidence that low serotonin can also play a role in the process.
One piece of evidence is that people who are very shy can actually lose their inhibitions when they use drugs that increase dopamine such as alcohol or cocaine.