I can tell you the difference. People with social anxiety may develop this at any point in their lives. Shy people are born that way. Social anxiety can also be different for different people. I have it and I can go into crowds. I have a problem when there are too many people in a smaller space and it happens with people I know and I'm comfortable with. Usually family. This has never happened outdoors with me. Now here is the real difference. My husband is shy and doesn't talk much, but never panics or stresses. I'm not shy, but in the right circumstances when my anxiety kicks in, my heart will beat faster. I'll start clenching my fists and jaw and eventually, I'll start crying and hyperventilating. This is totally involuntary on my part, I simply cannot help it. A Xanax will fix it. Now, things that terrify most people don't bother me, like spiders and public speaking. I have no issue with small spaces by myself. It just has to be a certain combo and there's really only an issue with it a few times a year, like holidays. So shyness is uncomfortable and a personality trait. Social anxiety is an illness and causes horrid mental suffering. Hope I helped.