Hypersensitivity: real, normal, and little understood.
“Highly sensitive people (HSPs) make up 20 percent of the population. Today, science is validating (this) group of people…who are taking in a whole lot of subtleties that the other 80% of the population don’t even notice. HSPs are likely to answer yes to so-called ‘thin-boundary’ questions such as ‘I have a rich, complex inner life’, ‘I am made uncomfortable by loud noises,’ ‘I am really particular about what kind of fabrics I wear,’ “my moods are very reactive to both what’s going on around me and what’s going on inside me,’ “I am very sensitive to smells’ …some to the degree of reporting being disabled by exposure to colognes, paints, pesticides, and other trace elements in air.”
If you are or love an HSP…
“HSPs occur at a significantly greater rate among artists and musicians than in the general population. While their moods can lead to greater incidence of anxiety and depression, it also appears that their images of beauty are more vivid…as if HSPs alone see the world in high-def. On the plus side, a simple “nice job” might lift an HSP child into game-changing positive effects…say, by studying extra well for the next test. At the other end, ridicule or bullying could snowball easily into despair and futility for an HSP child. School and parenting practices can dramatically enhance the development of these children by recognizing that they can thrive spectacularly in a mildly encouraging classroom or struggle endlessly in a slightly discouraging one, while a less sensitive child is likely to respond about the same regardless of similar variations in the classroom environment. As adults, HSPs are likely to make especially compassionate friends who truly care about others, channel beauty from the world into art and music, home and work activities, and notice things others miss. So, rather than come down on an HSP to ‘toughen up’, think about the importance of being supportive and patient…which can go a long way with both the giver and the receiver of that support.”
[Most of material from “Sense and Sensitivity” by Andrea Bartz in Psychology Today, p 72-79, July/August 2011]
Dr. Sharon's Surf Your Soul Weblog 
Your points about encouragement and discouragement are dead on. I know from personal experience, how important encouragement is for HSP’s. Highly sensitive people take everything to heart. They are also likely to treat all input as valid so as children are extremely vulnerable to negative perception and intent.