Upper respiratory infections (URI) as a group are responsible for 50% of all acute illnesses, with the common cold syndrome being most familiar. Colds are caused by over 200 viruses and are characterized by sore throat, congestion and mucus secretion. When exposed to viruses or other infectious agents, only a proportion of people develop clinical illness. Reasons for variability in response are not well understood and the possibility that psychological factors play some role in the aetiology and progression of infectious disease has received increased attention.

It is commonly believed that stressful life events influence the onset of URI by causing negative affective states (e.g. anxiety and depression) which, in turn, exert direct effects on biological processes or behavioural patterns that increase disease risk. The influence of stress on the immune system is considered the primary biological pathway through which stress can influence infectious disease susceptibility. While there is substantial evidence that stress is associated with changes in immune function (Herbert & Cohen, 1993; Segerstrom & Miller, 2004) (see ‘Psychoneuroimmunology’), the implications of stress-induced immune changes for susceptibility to disease have not been established. To date, studies of stress and URI susceptibility have focused on establishing a link between stress and disease with little attention to pathways through which such an association might occur. The major findings of these studies are examined below.