The main symptoms that distinguish Social Anxiety from shyness are:
-The intensity of the fear and anxiety felt
-The impairment of everyday functioning that it causes in a person’s life
-The level of avoidance
Shyness: People who are shy may feel uncomfortable, but after being in a situation for a while they usually warm up and find that they can relax. It might feel awkward talking to people, but it’s not impossible and doesn’t result in intense anxiety.
Social Anxiety: A more extreme fear of particular social/public situations. Sufferers will often fear being embarrassed, or worry about being negatively evaluated by others. Anticipatory anxiety and avoidance are common, and individuals may endure social situations with a high level of discomfort. The scope of the anxiety may be focused on specific settings or generalised to almost any social/public encounter.
Although many people experience some shyness and discomfort, especially in new situations or with unfamiliar people, it’s generally tolerable. For those with social anxiety some situations will be nearly intolerable – they find it impossible to relax and the anxiety and emotional distress tend to intensify rather than dissipate.
Please also see these pages :
Difference between social anxiety and performance anxiety
www.aboutsocialanxiety.com/social-anxiety-vs-shyness
www.aboutsocialanxiety.com/introvert-vs-extrovert/
www.calmclinic.com/social-anxiety/shyness
www.socialanxietyinstitute.org/shyness-or-social-anxiety-disorder
www.verywellmind.com/difference-between-shyness-and-social-anxiety-disorder