Difference between preventions, treatments, and cures

A prevention or preventive measure is a way to avoid an injury, sickness, or disease in the first place, and generally it will not help someone who is already ill (though there are exceptions). For instance, many babies in developed countries are given a polio vaccination soon after they are born, which prevents them from contracting polio. But the vaccination does not work on patients who already have polio. A treatment or cure is applied after a medical problem has already started.

A treatment treats a problem, and may lead to its cure, but treatments more often ameliorate a problem only for as long as the treatment is continued. For example, there is no cure for AIDS, but treatments are available to slow down the harm done by HIV and delay the fatality of the disease. Treatments don't always work. For example, chemotherapy is a treatment for some types of some cancers, which may in some cases enact a cure, but not in all cases for all cancers.

Cures are a subset of treatments that reverse illnesses completely or end medical problems permanently.