Ninety years ago, when Sir Alexander Fleming discovered that bacteria left in a petri dish was killed by mold, a revolution in modern medicine began. Since 1928, penicillin and other antibiotics have saved millions of lives. But even this medical miracle has its limitations — and can do harm when not used properly.

This year throughout Global Antibiotics Awareness Week (Nov. 13-19), the World Health Organization underscored the importance of seeking advice from a qualified healthcare professional before taking this class of drug. If misused, bacteria can actually build up immunity to these life-saving medicines rending them ineffective. This resistance can be particularly threatening for people with rare immune disorders, including cystic fibrosis, babesioisis or Lyme disease. For this reason, WHO advises seeking the advice of a health practitioner before taking them. In fact, the WHO created a nifty graphic to drive the point home. Check it out here.