User blog comment:Ddlcmc/Hey! i know the drawback to shoto's fire quirk!/@comment-32705196-20180406215124/@comment-24442815-20180406223018

I'm pretty sure this was addressed in one of the Volume Extras pages where they show his costume and how it warms him up and cools him down in order to maintain homeostasis. Also a more scientific explanation in case you're interested https://askabiologist.asu.edu/bird-hypothalamus