There are two serious misconceptions about hypothermia and frostbite that have somehow made their way into Boy Scout trainings, college outdoor club trainings and even into some outdoor education groups.
The first myth is that you should get naked and get into a sleeping bag with someone who is hypothermic.
This is false. If you get into the sleeping bag, you will be unable to treat the person. You may also need to get in and out to facilitate other aspects of rewarming and/or a potential rescue.
The second myth is that you should warm a frostbitten limb next to a fire.
This is also false. If you try to warm a frostbitten limb next to a fire, you will do severe nerve damage. The same is true for rubbing a frostbitten limb. The best thing you can do with frostbite is to slowly rewarm the limb.
When it comes to rewarming a person that’s hypothermic in the field, often the best response is to put them into a hypowrap (or a burrito). Here’s a quick video on the topic:
More information about the construction of a hypowrap may be found here.