Pain is defined by the International Association for the Study of Pain (IASP) as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”

The definition is important because it links emotion and past experience to the sensory event. This means that the only way of deciding whether someone has pain is by asking them or picking up clues from the way they behave.

Some pain is easy to understand because there is an obvious injury such as a cut or a bruise. Other pains are less obvious. For example, you cannot see the pain of appendicitis, but anyone who has had it will tell you that it is real enough.