Evidence suggests that thin boundary people are highly sensitive in a variety of ways and from an early age:

• React more strongly than do other individuals to sensory stimuli and can become agitated due to bright lights, loud sounds, particular aromas, tastes or textures.
• Respond more strongly to physical and emotional pain in themselves as well as in others.
• Become stressed or fatigued due to an overload of sensory or emotional input.
• Be more allergic and their immune systems are seemingly more reactive.
• Be more deeply affected -- or recall being more deeply affected -- by events during childhood.

(all part of being an empath; i would assume)