Herpes vs. canker sores:
There was a point where i wasn't clear on the difference between herpes or canker sores either, so i did a little research.
Well, i knew what canker sores were since i've gotten them my entire life, or at least as far back as i remember, i just wasn't sure if they were the same thing as herpes, but it quickly became apparent that they weren't.
Canker sores are pretty much an enigma. It's pretty certain that they're inherited, and it's known they're not contagious, but because of that they haven't really gotten a great deal of research allocated to them. They're ulcers that appear inside your mouth on the inside of your lips/cheeks or occasionally on your gums. They can appear due to some kind of trauma (say, biting yourself) or just randomly.
Herpes on the other hand is a virus and is contagious. There are two kinds, HSV1 and HSV2 (short for Herpes Simplex Virus.) At least there are two kinds of you're talking about STDs, there are a couple other related viruses, including chicken pox. In fact that affinity to chicken pox used to make testing difficult because if you'd ever had chicken pox then you would get a false positive for HSV1/2. However the newest tests have improved and can now tell the difference.
I believe that _usually_ you get HSV1 orally and HSV2 genitally, however they _can_ cross-infect.I believe that if you catch one it gives you some resistance to the other, but it is _not_ a guaranteed thing, you can catch both. I believe herpes shows up as blisters, rather than ulcers, and if you have the oral version it will generally show up on or around your lips, not inside your mouth.
And yes, a large percentage of people have at least one form of HSV, i don't know the exact percentage but 50% probably wouldn't be unreasonable. I believe that the majority of that is HSV1 rather than HSV2 (which i think might be more serious) but i'm not sure.
Okay, i think that's most of what i know, and it's been quite awhile since i looked it up so there's no guarantee about the accuracy, except for the bit that canker sores and herpes are indeed different things :) Of course you could probably go check out wiki and find a great deal about the subject, but i'm too lazy for that right now :)