Aids to Health

The body resists disease through immunity. Some immunity is innate - you are born with it, inherited from your parents, and it acts against many germs in a general way. The rest is acquired during life. Acquired immunity splits into two: active immunity, where your own body makes antibodies, and passive immunity, where ready-made antibodies are given to you from an outside source. Together these layers keep most infections out.

Active immunity develops when your body meets a germ - either a real infection or a weakened germ in a vaccine - and responds by making its own antibodies. It takes a few days to build but lasts a long time because the body remembers the germ. Passive immunity is different: ready-made antibodies are simply handed to the body, such as antibodies passing from mother to baby through the placenta or breast milk, or an anti-venom injection after a snake bite. It works instantly but wears off quickly because the body never learned to make those antibodies itself.

Vaccination means putting dead or weakened germs (or their products) into the body so it builds immunity without suffering the real disease. This gives artificially acquired active immunity. Edward Jenner pioneered this with smallpox. Common vaccines you should know include BCG (against tuberculosis), DPT (against diphtheria, whooping cough and tetanus), TAB (against typhoid), and the polio vaccine. Because the germ is harmless, the body safely learns to recognise it and is ready if the real germ ever attacks.

These chemicals fight germs outside and inside the body. An antiseptic is mild enough to use on living tissue - on skin, in mouthwash, on a wound - to slow or kill microbes (Dettol, iodine, Lysol). A disinfectant is much stronger and is used only on non-living things like floors, drains and instruments because it would damage living tissue (phenol, cresol). An antibiotic is a chemical made by one microorganism that kills or stops the growth of other disease-causing microorganisms; penicillin, the first antibiotic, was obtained from the mould Penicillium notatum by Alexander Fleming.