Serge King, an old Hawaiian Shaman, says, "When you criticize yourself, your [internal power source] feels under attack and tries to defend itself by clenching muscles, which causes stress and inhibits awareness, memory, and energy flow, making you weaker and more subject to illness and accident."
Horrible, isn't it? I've seen it happen to myself and others time and again. Self-criticism creates stress, which turns into toxins in the blood, and from there into illness if you don't take a purifying course of action (such as drinking water, getting fresh air, sleep, and exercise).
But here's something really profound, said by the same man:
"When you criticize another, your [internal power source] takes it personally and your body gets tense..."
Your own body TAKES IT PERSONALLY! WHAT?!!! That's right. When you say mean things about someone else, your body takes it personally. I knew this wisdom a long time ago, and so I mostly stopped talking about people. I try very hard to air all of my issues immediately so they don't fester. If I catch myself gossiping, I try to look at the deeper reason.
My understanding of this energetic process of Criticism is that when you criticize someone with the intent to bring about transformation (either yours or theirs) in the Spirit of Love, all of that potential negativity is transmuted into something healing and empowering.
If, however, you criticize behind someone's back and choose to nurse those judgements without airing them, they become toxic to you and everyone else who hears them. You become a psychic drain on yourself, promoting your own illness.
Some people are afraid of the conflict that sharing their true feelings will bring. But by opening our hearts to universal love and compassion, and then aligning with our personal truth, we step into our own power. Criticism (for self or others) falls away.
Lastly:
"When you praise another, your [internal power source] says thank you and your body relaxes."
So Praise! Praise away! You feed yourself and others with good words!