Most of the research into social phobia has been conducted over the past decade or so; although it is easy enough to trace it back at least a further decade. A variety of different explanations arise but the most dominant theory today was first proposed by Clark and Wells in 1995. They suggested that people with a social phobia go through a characteristic three stage process.
Stage 1: People with social phobia hold a set of beliefs about themselves that ultimately set the scene for difficulties during social encounters. Sometimes these same people can remember one or more key moments during their early years that have since developed into a negative association. For example, a comment about some physical aspect like body odor or sweaty palms, or the fact they dressed inappropriately or sounded nervous. This type of comment or interaction can develop to a point where social interaction is seen in a negative way and also interpreted in a negative way. An example of this might be a host who abruptly switches their attention from you to someone else. Your interpretation of this could easily be they find you boring, whereas a more likely reason is they need to welcome another guest. In such a scenario an anxiety response can be triggered that involves physical symptoms (feelings of nausea, headaches, cramps) psychological symptoms and a need to avoid or escape the situation.
The memory of such social interactions can quite easily lead to a point where future social interactions are avoided because failure or rejection is expected.
Stage 2: involves the social interaction itself. At the first sign of social threat the person feels their body responding by trembling, increased pulse rate, mental blanks and feeling flustered. In fact any one of these symptoms can quickly lead to a cascade reaction of symptoms.
As a means to reduce the sense of threat, the person is likely to use one or more safety behaviors. Typically this will involve some action that helps to avoid a feared outcome. Holding a glass and/or a plate of food is a way to avoid hand shaking for example. Clark and Wells suggest that a crucial feature is the way a person with social phobia then turns their attention inwards. Any sense of being evaluated by one or more people causes the person to monitor their own behavior. They start to form an image of how they must look to other people. They begin to see that others can see their lack of certainty and maybe the fact they are trembling.
Stage 3: involves a process of self-evaluation and recrimination following a social exchange. They characteristically evaluate their performance as negative or ambiguous at best. Ambiguities frequently become recast as negative and the whole process feeds back into the beliefs they hold about themselves and as previously outlined in stage 1.
Clark, D.M. & Wells, A. (1995) A cognitive model of social phobia. In Social Phobia - Diagnosis, Assessment, and Treatment (eds R. G. Heimberg, M. R. Liebowitz, D. Hope, et al), pp. 69-93. New York: Guilford.