Antibiotics do not affect Candida, which is both a yeast and a fungus. This allows the Candida to grow wild in the colon. While small amounts of Candida are harmless, larger amounts are not. Some harmful bacteria are also immune to some antibiotics. These can also grow wild when a person takes antibiotics.
Some antibiotics are safer than others.
Tetracycline is among one of the worst. See the Safer Antibiotics for more information. The growth of Candida in the colon can also be encouraged by the consumption of sugar, alcohol and by food allergies . Candida feeds on simple sugars. Food allergies inflame the colon, which encourages more Candida growth.