Most people can eat a whole pineapple with no problems, others can't. Instead of eating a 1/2 of a pineapple, just eat a piece each day and try 1 pineapple in a weeks time.
I don't know if the reaction is a result of the person's internal health, after you eat the pineapple drink some water and get it off your lips/mouth, etc. Pineapple is a powerful food, yet safe enough most 2 year olds love it.