We call them “friendly bacteria,” and they have a symbiotic relationship with us. We help them by giving them a place to live and food to eat, and they help us by producing nutrients such as B vitamins, helping to metabolize drugs and hormones, and maintaining a healthy pH balance in the intestinal tract.

Friendly bacteria also protect us from infection by bad bacteria. For the most part, they do this simply by being more numerous: With good bacteria occupying most of the available space, there isn't room for bad bacteria to thrive.

But when something happens to disrupt the balance, bad bacteria can start to outnumber the friendly kind, and illness occurs. What causes this shift in bacteria population? Paradoxically, taking antibiotics can actually be one of the major causes of having too much bacteria. Most antibiotics kill all bacteria indiscriminately, including the good kind. If more good bacteria dies than bad bacteria, the bad kind will start to take over.

Birth control pills and other hormones (including steroids) can disturb the balance, too. In addition, an unhealthy diet, too much alcohol, and too much stress will nourish the unfriendly bacteria while killing the friendly bacteria.

One of the most plentiful harmful bacteria is the genus Candida (usually Candida albicans, specifically), a type of yeast that lives in the small intestine, the urinary tract and the mucous membranes. Normally, Candida's numbers are kept in check by friendly bacteria. When it is allowed to flourish, however, it causes dysbiosis -- the opposite of symbiosis, where one organism is now harming the other -- and illness.

Symptoms of Candida dysbiosis are often reminiscent of a hangover. Why? Because Candida is a yeast, and yeasts produce ethanol (or alcohol), as well as acetaldehyde -- the main chemical responsible for hangover symptoms. If there is too much Candida, too much alcohol is produced, and the person experiences the side effects of drinking without touching a drop!

Too much Candida can manifest itself in these symptoms: fatigue, headaches, aches, weakness, general “hungover” feeling, lack of concentration, diarrhea, nausea, constipation, allergies, and vaginitis, among other things.

In addition, while Candida is normally a bacteria, when it becomes strong it can change into a fungal form, with little branching “arms” that can jab into the intestinal wall. This leads to something called “Leaky Gut Syndrome,” which is exactly what it sounds like: a permeable intestine that allows toxic chemicals to escape and be absorbed into the body.

One of the simplest ways to avoid all this unpleasantness is to resist taking broad-spectrum antibiotics. They may help with the immediate condition that requires treatment, but they may be more harmful in the long run. With several hundred types of bacteria in your system, most of them beneficial and necessary, it's best not to send medication in that's going to wipe them out.