What precautions are to be taken by a therapist before embarking systematic dese!

What precautions are to be taken by a therapist before embarking systematic desensitization?

I would say the most important factor is that it is needed to be kept in mind that phobias are self-reinforcing avoidance behaviors.

Example: Triskaidekaphobia is the fear of the number 13. There is no actual way a number can hurt you by itself so this is a good example. Many cognitive scientists and psychotherapists will argue that there has to be a trigger event for a phobia to start, such as being frightened by a loud noise while seeing the number 13, but as you will see this is not the case. There does not have to be any danger at all, and no threat. Only the perception or imagining of a threat. The subject has heard been exposed to common myth that the number 13 is unlucky, so at a race track they bet against a horse numbered 13 and they win. Avoidance has been reinforced. Later, they are are asked to bring 13 staplers to a room where they work. Because of previous reinforcement, they bring 14 staplers and they are thanked for bringing the extra one. Avoidance has been reinforced again. Note that in both cases there has been no instance of terror and no threat. The subject will begin avoiding any circumstance involving the number 13, and he will become increasingly upset when he cannot avoid these circumstances. Over time, however, the person's avoidance behaviors may become more serious, leading them to deeper avoidances of the phobia, ones that may affect every-day life in negative ways.

So bearing that in mind, the therapist must absolutely be aware of any circumstance that the patient may engage in during their treatment that may further allow or reinforce avoidance behavior. If the patient is allowed under any circumstances to further avoid the object of the phobia, or worse yet, if they are reinforced for their avoidance, then it will be a circumstance where the psychologist is actually aiding the maintainance of the phobia.