Urticaria, known as hives in the United States and Norfolk, is the comparatively common rash that looks as if it is the result of a nettle sting. The rash is raised and itchy with red and white inflamed patches of variable size and shape. These weals are transient, but no sooner has one area of the skin cleared than another may be affected.

The angioedema that is often associated with the urticaria is the result of a swelling of the subcutaneous tissues. Because of this swelling, the area around the eyes, face, lips and tongue, the genitals, and the backs of the hands and feet are puffy and swollen.

Angioedema always causes anxiety, as there is a fear that, if the swelling extends into the throat, the breathing may be impeded to a varying extent. The patient may then develop a rasping respiration with loud, laboured breaths.

I have the impression that the grandmother hasn’t noticed any respiratory problems, and that her principal concerns are that the rash and swelling show no signs of disappearing, that the itch is distressing and the weals and facial swelling are disfiguring.

Usually each attack of urticaria and angioedema lasts less than six weeks and is caused by an allergy. Careful history- taking will usually elicit the trigger-factor that has caused the skin troubles, as the patient will get another attack once their immune system is again confronted by it. Commonly the triggers are a particular food (sometimes fish), contact with a metal, a drug, one of the dreaded Es that are used to colour or preserve modern food, or some other chemical. Transient attacks can usually be shown to have an allergic origin, as the immune system shows what is known as an IgE-mediated response that can be detected in the patient’s blood.

The chronic urticarial and angioedematous response doesn’t always have an allergic origin, and hence IgE response. The truth is that, if there isn’t an obvious allergy, doctors are usually stuck for a diagnosis and hence label the condition idiopathic urticaria.

There are one or two very rare conditions that should be excluded. There is a hereditary form of urticaria and angioedema that results from deficiency of a protein, known as a C1 inhibitor. In 50 years of medicine, I have come across one case of this, which was in a man at a dinner party in Italy. In other cases, the angioedema may be the result of an unusual condition known as erythropoietic protoporphyria. This form of porphyria usually becomes obvious much earlier in a child’s life, as they develop an unpleasant light-induced skin rash while still in their cots.

Acute attacks of urticaria can be treated with antihistamines. If the attack is more severe, steroids by mouth may be indicated, but the application of steroid creams gives only momentary relief. If there is significant obstruction to breathing, or any signs of anaphylactic shock, including nausea, vomiting and gastrointestinal upset, adrenalin injections may be necessary. Fortunately, our reader’s granddaughter’s troubles don’t seem to belong to this category.

Any other drug that a patient is taking should be discontinued, so that the effect of leaving it off may be assessed. Likewise, other typical allergy-inducing triggers should be sought and excluded; the list includes metals and chemicals, including those in skin preparations and food allergies.

Angioedema and urticaria are worse if the patient is stressed, ill, tired or has been exposed to an overdose of sun. I had one patient who developed urticarial angioedema if she drank beer — but only if she had drunk it when anxious as the result of flying.

St Mary’s Hospital in London has an excellent allergy centre for children, while Yorktest Laboratories in York has well-qualified staff who specialise in detecting allergies.

Send Dr Thomas Stuttaford your questions on allergies http://www.timesonline.co.uk/talkingpoint

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