We all have mirror neurons in our brains, which is why we might cry when we see someone else’s tears. But people with mirror-touch synesthesia are believed to have overactive mirror neurons, making their responses much more extreme. The condition causes people to literally feel the physical sensations when they watch another person being touched. Just seeing glasses on someone else’s nose can make sufferers react.
I had this type of synesthesia when I was younger (approximately up to the age of 6). Now I only have sound-color-shape type synesthesia (I see colours and shapes of music, sounds in general) and smell-color synesthesia (I can see colors of different kinds of perfume/smells).