If you're struggling with fatigue or weakened immunity (this time of year, who isn't?), try this tip from Mark Hyman, M.D.: At the end of your shower, alternate between hot and cold water for a few seconds each, going as far in each direction as you can stand. The swings in temperature increase circulation, which flushes the lymphatic system -- an important component of immunity. The practice is also intensely energizing: Your skin will tingle and you'll feel raring to go. And, perhaps, inspired to skip that second cup of coffee or tea.
For more ways to maximize your body's immune system, read more of Dr. Hyman's detox tips.
Tell us if you're up for this Challenge of the Day after the jump.