Frostbite

If a creature has been in areas of extreme cold, they risk getting frostbite. The creature must have already gained at least one level of exhaustion before risking frostbite.
At the end of each hour the character must succeed on a Constitution saving throw, where the DC is 10 + the total number of hours exposed to extreme cold or suffer the effects of frostbite.
Frostbitten characters make Dexterity- or Strength based ability checks, attack rolls, and saving throws with disadvantage.
Treating frostbite requires three successful DC 15 Wisdom (Medicine) checks. These successes do not need to be consecutive. Only one Wisdom (Medicine) check can be attempted per day for frostbite. If the creature is near a source of fire, like a campfire, this check is made with advantage.
A lesser restoration or similar spell will heal frostbite.