I must admit this is something that I'm not familiar with. I've seen angio-oedema - a severe allergy reaction which causes swelling of the lips and tongue - but not a condition which just causes itching of the roof of the mouth. I took comfort from the fact that Patient 1's doctor was stumped too.

However, Patient 2 posted the answer; this was probably oral allergy syndrome (OAS). Apparently, it's also known as mouth and throat allergy syndrome. As well as the severe form I know about, it can also cause a whole spectrum of less life-threatening conditions, including itching of the roof of the mouth without the swelling of the tongue and lips. Colleagues have advised me that OAS is not actually that uncommon.

Is it hay fever?

Patient 3 pointed out that OAS usually occurs in people with hay fever. People who have an allergic reaction to certain pollens can have a cross-allergy reaction, developing OAS symptoms when they eat certain foods.

OAS has recently been given another name: pollen-food allergy syndrome. Four out of ten hay fever sufferers who also have this condition are allergic to silver birch tree pollen. The allergy-causing chemical (allergen) in this type of pollen is very similar to that found in apple, hazelnut, carrot, cherry, pear, tomato, celery, potato and peach. So people with birch tree pollen allergy can be allergic to these fruits and vegetables as well. People with grass pollen allergy can react to melon, orange and wheat, whilst mugwort cross-reacts with apple, carrot, celery and melon.

Patient 4 found that she suddenly developed an itchy mouth after eating strawberries, even though she had never had problems with them before. Patient 2 reacted to apples and almonds, and Patient 5 had problems with raw onions. In some people, the trigger seems to be non-food related. For Patient 6 it was cats, and for Patient 7 it was dust.

Patient 8 emphasised that a number of other conditions need to be ruled out, particularly if the symptoms appear unrelated to an identified trigger factor, and/or there are areas of discolouration, patches or ulcers on the roof of the mouth.

Of course, as Patient 9 discovered, frequent rubbing of an itchy mouth can cause an ulcer, but you shouldn't assume that this is the cause. Fungal and bacterial infections, dental problems and even tumörer may need to be excluded.

With regards to treatment, Patient 10 made the sensible suggestion that if you identify a trigger, avoid it. The severe reaction (called angio-oedema) is rare but swelling of the part of the larynx called the glottis is occasionally seen. So it is worth knowing what foods you are allergic to and need to avoid.

Patient 11 and Patient 6 found that it helped to keep well hydrated and that if they did not drink plenty of water throughout the day, their itching got worse. I can't find anything in the textbooks about this, but it makes sense to me and can't do any harm.

Patient 7 and Patient 12 reported that they got some relief by creating a vacuum at the back of the throat and forcing air through it with the tongue. Unfortunately, this results in a rather startling noise so it is not something they do very often in public!

Patient 11 and Patient 13 found antihistamine tablets such as fexofenadine helpful, but many other posters were not that impressed. I found this surprising considering that allergy was the main identified cause, and that the textbooks identified antihistamines as the mainstay of treatment.

Patient 14 found the gabapentin she was prescribed helpful and that the itching was worse during times of stress. Gabapentin is a medicine which calms down inflammation in the nervous system, which suggests to me a cause unrelated to allergy. Patient 10 obtained relief from amitriptyline, an older prescription-only medicine which has a similar effect to gabapentin, but has more side-effects in some patients.

Heat apparently reduces the allergic effect of some fruits. This seems to work best where apples are the cause. For really persistent symptoms, the textbooks recommend immunotherapy - a course of injections containing a low dose of the pollen the patient is allergic to, to reduce the body's reaction to it. The theory is that this will reduce cross-allergy reaction to the associated trigger food.

Steroid tablets are another option. They are only available on prescription, have long-term side-effects, and are usually given as a short course for really troublesome symptoms.

I've just remembered that I have seen this condition before, not in my professional life but within my own family. Whenever my grandfather looked at the Grand National runners he used to get an itchy throat when he spotted a potential winner. I've no idea what the pathology was there, but in view of his success rate, I thought you ought to know.