[ Cisco knew that he was probably being silly and overreacting, even as he led Rey towards the cabin. Surely she would have noticed, if her hands were getting dangerously cold? But then, another voice in his head interjects, she is from a desert world. She might not know about frostbite, might not know how to recognize the signs... ]

It is something to worry about.

[ Something's gone a touch tight in his voice. He opens the door and ushers her inside, leading her over to the small sink in the kitchen. The cabin is cozy, the light inside orange and warm and flickering from the fire. Cisco tugs off his mittens and turns on the water, testing the temperature. He starts it off cool, then gestures for Rey to put her hands under the flow. They don't look too bad, but that doesn't mean he can get careless. ]

Have you heard of frostbite? You can hurt yourself really badly, if you're not careful-

[ Very gradually, he adjusts the temperature of the water, a little warmer. He'd seen how this worked, had read far too many websites about it, after what had happened to Dante...

Cisco realizes that he is gnawing at his lip, anxiety all too easy to read. He knows he should explain, that he owes Rey that (even if he is right). ]

My brother- he got hurt really badly.

[ It's only a partial explanation, but it's a start. ]