You may have heard the saying, "I like who I am when I'm with you." The author of those words is self-aware, recognizing how the moods and attitudes of others affect her mood. Knowledge is power when it comes to the phenomenon of social contagion. When you are around someone who is in a negative mood and you feel your mood sinking, take action to change your mood by being more conscious of what is going on. Think about what you feel and make choices. Make your mood a decision, not a reaction.

Often, an individual tries to "help" the person who is in a negative mood out of a perceived notion that he is interested in the other person. But that may not be the case, writes Dr. Alex Lickerman in a Psychology Today article, "How to Manage Your Partner's Bad Moods." The real reason for trying to resolve another person's bad mood can be your way of avoiding getting into a bad mood yourself. If another person's bad mood is having a negative effect on you, don't try to fix it unless you did something to prompt it.

Negative moods can be draining, not only for the person who is in a negative mood, but for others. If you have a family member, coworker or associate who tends to be in a negative mood frequently, plan a self-defense strategy. Think about how you will give support. Listen, but resolve to remain detached. Have a plan for taking a break from the person for a while, if needed. Running errands, doing chores or taking a shower can give you a mental break to regroup and recharge.

Let your positive mood -- whether it is bubbly happiness, calm serenity or something in between -- set the tone. When you find yourself in the presence of a negative person, make an effort to display a positive mood. Be aware of the tone of your voice and body language. Make eye contact and smile. Facial expressions trigger a mirror response in an observer, causing that person's brain to respond in a similar manner.