No interaction whatsoever with entrance/first landing page of your website by the visitor during a session shall be treated as bounce rate.
Causes of bounce rate:
1) Usability issues
Bookmark a page to load in a browser tab everytime user opens a new browser and not interacting with the page can be considered as bounce rate.
Several other attributes constitute to user behavior that can be considered as bounce rate.
2) Site Design
Though the pages are tagged properly and still experiencing the high bounce-rate try change the design and layout of the landing pages.
Optimize the pages with relevant search terms that bring more users.
Use Menus with links that can lead to more appropriate information which user may find relevant (or intended to visit) to the entrance page.
3) Found the information required quickly and left the page.
You can do very less about the this case except changing the time settings in analytics to appropriately measure your bounce rate.
4) Single page site - No internal links to follow and a page refresh can only effect the bounce rate metric.
5) Implementation Issues - Missing the tracking code in the subsequent pages in multi-page website.