Yeah, because the more tails he has active, the more damage is done to his body. After he used one tails, nothing noticeable was wrong. With four tails, he skin was burned red. So the more tails on him, the more damage he is under. Or at least that was the case. Now with the nine tails chakra mode, he shouldn't have to worry bout that lolI think that might be right but even having the nine-tails inside of him when he went into to six-tails ( correct me if i am wrong) when battling nagato after his tranformation was done and he went back to his regular form his skin was completely torn off and it took several days to heal even tho he has the nine-tails inside of him (again correct me if i am wrong)