Well, this list is very country specific. Here in the US, it is the big three, tobacco in all its forms, excessive alcohol consumption, (an independent cause - and a synergistic cause with tobacco when used together, and it thins the cell wall membranes allowing the tobacco carcinogens easier access to things) and HPV16. There are other causes that are minor, a very small percentage that have some unique genetic component, and of course bout 5% that we have no clue about that fall into no known cause.

However if you live in Sri Lank, Vietnam, India, etc. you can add to the list betel nut which is chewed with lime, (tried it in Vietnam, YUK!, but it has mildly narcotic effect on you... hey it was the 60's) quid, paan, (same stuff different packaging -commercal vs. loose leaf vs powdered) Those are the PROVEN causes. You will still see old info, mostly disproved causes, such as chronic irritation or oral health/hygiene, which have only been loosely associated with OC, and the ever present one, lichen planus which has never been proven to actually be a cause of, or an actual precancer condition, but is sometimes seen in conjunction with OC. LP has never been proven to actually cause OC, or develop into it. But the web, and even some really good sites still have some of these things up, to cover all bases perhaps (quoting articles that are decades old), but it is marginal info and leads people down the wrong paths. But the science is what evidence based science is, and except for some genetic abnormalities, and the few percent that fall in to no category that we can identify (a VERY small number) this is the list.