The actor blamed insect bites for his early departure, saying he was bitten more 125 times in eight days.
In a statement, he said the bites were so bad he had an extreme allergic reaction that caused him to lose sleep and 22 pounds.
The actor says he will continue to work on behalf of his chosen charity LOVE 146, which fights child sex slavery and exploitation.
The Hills stars Spencer Pratt and Heidi Montag have already walked out of the Costa Rican jungle so are out of the competition, which ends on Wednesday.