Melody: I have a 3-year old granddaughter who?s presenting a rash which is really concerning us. We?ve had her to a couple of doctors, we?ve had various opinions. It?s a rash that comes out like little water blisters, from the size of the head of a pin to the size of a match head, and which is surrounded by extremely inflamed skin, that when you touch it, is burning hot, and it literally makes her scream. It comes out in small patches, and we?ve had it literally cover both of her legs completely, but it comes and goes within 20 minutes.

Harry: So it comes and goes in 20 minutes? That?s really remarkable.

Melody: Sometimes even less ? sometimes ten minutes, She?s also had it in other places, such as in her hair. This has been going on now for about 5 days. I thought it was oranges.

Harry: I must ask you, Melody, is it itching at all?

Melody: It starts off itching, and then it?s obviously painful, too painful to touch. My son gave her an orange, to find out, and then she came out again in the rash.

Harry: Well, Melody, I think you have a remarkable family, a marvellous son. How old is you son?

Melody: My son is nearly thirty.

Harry: So, as a good scientist, a good investigator, he decided to do a diagnostic test, and he actually gave her what he thought was responsible. In other words, he observed her ? you?ve made the diagnosis by very careful and astute observation. You?ve done what we call a ?challenge test?. We do this when we suspect an allergy to something, then we challenge the individual. You?ve got to be careful incidentally, because sometimes these allergies can be very serious. So I want to mention, as a matter of principle, that if you do a challenge test, you should be careful, and it should really only be done in circumstances where you?ve got facilities for resuscitation. I don?t want to alarm you, Melody, but sometimes the reaction can be very severe.

It can involve, for example, swelling of the mouth and the tongue, people can have difficulty in breathing sometimes. It can involve the chest, which can close up and cause a very bad asthma attack. So as a general principle, it should only be done in a safe environment with facilities for resuscitation, for example in the doctor?s rooms. The other thing is, I think you might have to extend this to other citrus, not only oranges. You might have to be careful about lemons, grapefruit and other citrus fruits.