Let us consider smoking and oral cancer.
We know that smoking causes cancer (among a lot of other things), so do not want anyone to be exposed to smoking. Unfortunately, we are all exposed to passive smoke. What we can control is direct exposure through smoking ourself.
If one were to follow a person through time, the various interventions at each level would be as follows:
Primordial Prevention: Assume we are dealing with a small child. For starters, no one should smoke at home. At the very least, there should be no cigarettes/ bidis in the home environment. Legal measures ( prohibiting the sale of tobacco products to minors; prohibiting smoking in and around schools/ colleges, other educational institutions; creation of smoke free zones at work and recreational areas; prohibiting advertisements by tobacco companies; display of warning labels and graphic images on tobacco products; fines for offenders, etc.) will also be useful. Cigarettes would not be accessible to the child at this age if the above measures are implemented properly.
Primary Prevention (Health promotion, Specific protection): The child should be discouraged from acquiring the habit of smoking. By now, picture the child to be older, may be in the teens. Strong anti-smoking messages in school and at home, as well as education about the effects of smoking may help. At this stage the child has greater access to cigarettes. Once 18 years old, it will be possible to buy cigarettes legally. Even though purchase of cigarettes is legal at that age, we hope individuals will not purchase cigarettes as a result of the above measures.
Secondary Prevention (Early diagnosis and appropriate treatment): Unfortunately, the child (now an adult) has taken to smoking. He likes smoking with the burning end of the cigarette inside his mouth, and does so often, for its shock value. He develops a lesion in his mouth, and gets it evaluated by a doctor. The biopsy report says it is an early form of cancer. Surgeons remove the lesion, getting rid of the problem. Of course, he is advised to quit smoking for good.
Tertiary Prevention (Rehabilitation, Disability limitation): Assume he delayed evaluation of the lesion. By the time he does approach a doctor, the lesion has spread, and now involves his mandible (jaw-bone). The surgeons remove most of his jaw-bone to save his life. In addition, he undergoes radiotherapy. However, he can’t chew his food now (since the jaw-bone is partly missing). The surgeons fashion a jaw out of bone sourced from another part of his body. Intensive rehabilitation follows, and, almost 6 months later, he can chew much like he could before surgery.