I guess the word "sensitivity" can vary but I think we all have an idea on what it is generally.
I'm a triple scorpio (sun,venus,mercury) with Neptune,Moon and Uranus in the first house, Neptune squaring my sun, venus, and possibly mercury, Jupiter in Pisces 2nd house retrograde, moon sectile pluto as well. I believe I've been labeled as someone VERY sensitive starting from an early age. Sometimes, sensitivity comes from harships and experiences that trigger negative emotions within oneself, causing them to become an empath for others who are suffering as well. Sometimes, one can become sensitive towards another person's mood or emotions and can have difficulty defining it from THEIR emotions. Sometimes, being sensitive means being easily offended, hurt or taken aback.
I guess the planets Neptune, Moon, Pluto play quite of a lead role here, and it also depends on the aspects. The watery signs are known to be the most sensitive ones out of the 12 signs so even placements in any planet with those signs are bound to be sensitive to some degree. Neptune, I believe, creates more vulnerability and naiveness than Pluto and Moon. Pluto is like a warrior being destroyed but came back to life from ashes through transformation, while moon is almost like Neptune, just more motherly, and definitely knows its limits unlike Neptune. For me, Neptune is like martyr. I have this placement in the firsthouse (thank god its not really close to my ascendant though) and it still makes me feel dreamy, oversensitive, illusioned, naive but also a great empath and is a pro at putting everyone first rather than myself haha.
Chiron is where an individual has a... err, some kind of wound within? Not sure, but I remember it being labeled as the "wounded warrior" or something. Sounds like Pluto. I think Chiron is something you should definitely look for in a chart for more clues.
Having great sensitivity is a treat though. Makes you feel more human, makes you feel life itself even more. It also makes people like you, for nobody wants a insensitive human being. Being tough is great but it is also necessary for you to be soft too.