Repeated complaining rewires your brain to make future complaining more likely. Over time, you find it’s easier to be negative than to be positive, regardless of what’s happening around you. Complaining becomes your default behavior, which changes how people perceive you.
That's not all damage that you'll experience. Complaining too much can lead to heart disease, stroke, obesity and diabetes:
While it’s not an exaggeration to say that complaining leads to brain damage, it doesn’t stop there. When you complain, your body releases the stress hormone cortisol...
All the extra cortisol released by frequent complaining impairs your immune system and makes you more susceptible to high cholesterol, diabetes, heart disease and obesity. It even makes the brain more vulnerable to strokes.
It ruins life and health of others, too, though I sometimes think it's probably exactly what the downer's intention is anyway (remember the post about energy vampires?):
You need to be cautious about spending time with people who complain about everything. Complainers want people to join their pity party so that they can feel better about themselves. Think of it this way: If a person were smoking, would you sit there all afternoon inhaling the second-hand smoke? You’d distance yourself, and you should do the same with complainers.
Read the whole article over here. H/t to PJ Media.