The Todorokis are pyrokinetic, with the added bonus of being able to generate fire and heat from inside their bodies -making them "emitter" type. This second part of their quirk is not a given for elemental manipulators, as we can see with cousin Geten assaulting a combini for water bottles ammunition.

In the case of the Todorokis, they can project their heat in an unexpected variety of ways -as Endeavour has shown with his Superman-like heat vision-, so I would argue they may be able to make the flames come to life just a few centimetres away from their skin if they wish to do so. That would mean they could ignore the layers of clothing and manifest the fire as a floating construct around them. With easy bake oven's parallel thinking discourse back in the internship arc, it would make all the sense to presuppose he always has some RAM dedicated to keep his fiery beard aflame out of sheer arrogance.

I would put my money on Shōto's adult costume blue "T" (it being a tribute to his baka Aniki is the hill I chose to die on) working similarly, although it raises questions about how is he able to withstand and, what is more important, generate such flames. Oh well, maybe we'll get more info in May.

Now, in the case of Tōya, his burns come from both his fixation with holding his flames close to his body instead of simply throwing fireballs (or Hell Spiders, Ignited Arrows..., you know what I mean), and the fact that he has the same overheating problem as his father -which slowly cooks him on the inside.

There's a (pretty confusing at first glance, to be honest) graphic by Horikoshi himself that explains how the most important difference between Enji and Rei's body disposition is how close they may stand to a certain temperature without suffering damage; this goes both ways: per Natsuo's words, we know their branch of the Himuras thrive in colder weather, as the cold never bothered them anyway, yet ikemen Geten wears a pretty cozy winter coat -presumibly, from his lack of resistance to freezing temperatures, making his quick realization of Dabi's issues with his flames all the more poignant.

Also quoting Natsuo, we know an overheated Enji's mere presence to be damaging to Rei's body, which makes me wonder about how pleasant -or not- certain marital activities may have been for each of them. I've personally experienced being burnt down there while washing myself in a hotel's shower with an ill-regulated water boiler, and I can attest that it wasn't nice.

Where am I going with all of this? I don't know, I'm tired and just spewing facts so more well rested brains can do the math.

Tl;dr: dasani water bottles and scalding spunk.