Difference between OCD and hypochondriacWatch
Health anxiety isn't classed as an OCD disorder. It's listed by some people as part of 'OCD spectrum' which is not an official term, just like purely obsessional OCD isn't an official term. Health anxiety is compared widely to OCD in many books.
There isn't much difference between OCD and health anxiety in some cases. So health anxiety can be more visible where it leads to people who aren't put off going to see the doctor, these patients can have very excessive visits and tests. People worry about big things like cancer or ulcerative colitis. There can be a lot of rituals and tapping or checking behaviours. It's not talked about much but quite a few people in their teens, 20s and 30s probably have health anxiety. Other people with health anxiety it takes over their lives but they won't see doctors at all and spend a large amount of time ruminating over whether they have a disease of not (real or imagined symptoms) and researching it, often with excessive supplements or lifestyle changes. Reassurance behaviours tends to present themselves more in health anxiety than it does with OCD.