An infection is caused by the over-growth of a micro-organism somewhere in the body. Micro-organisms include bacteria, viruses and fungi amongst others. Bacterial infections are treated with antibiotics such as amoxicillin, erythromycin and ciprofloxacin. There are many different types of antibiotic, with different ways of working; the choice depends on the type of infection you have. Fungi commonly cause skin infections such as athlete's foot and ringworm. Antifungal medicines like miconazole and nystatin can be taken by mouth or applied directly to the affected area. Aciclovir is an antiviral medicine used to treat viral infections like shingles and herpes.