Peanut Allergy is usually a life-long allergy affecting 1.9% of Australian infants. A recent study in the USA shows that 1.1% of the general population have peanut & tree nut allergy. Peanut is the commonest cause of death due to foods.
Three key points characterize peanut and nut hypersensitivity:
- The reactions can be extremely violent and life threatening with minimal exposure. The amount of allergen required to induce allergic symptoms may be as low as 0.10mg (1 peanut is approximately 180mg) equivalent to 1/2000th of a peanut. Symptoms have been known to develop after kissing someone who has eaten peanuts
- Peanut allergy is likely to persist throughout life (especially if there is strongly positive skin prick test reaction to peanut & if associated with other food allergies)
- Peanut (legume) allergy is frequently associated with other non-legume (e.g., nut) and seed allergy. Peanut and tree nut allergic reactions coexist in one third of peanut allergic patients.
The commonest manifestation of peanut allergy is with acute urticaria (hives) following exposure. However, some patients may rapidly develop angioedema, bronchospasm and anaphylaxis.
Relative frequency of symptoms of peanut Allergy from a study in France:
Atopic dermatitis 40%
Urticaria & Angioedema 37%
Anaphylactic shock 6%
Digestive symptoms 1.4%
Peanut Reaction to first exposure
In one study 81% of children reported reaction on first exposure to peanut. This raises the question about how sensitisation occurs and is important to remember when giving advice on preventing allergies.
Peanuts are among the most allergenic foods. The peanut allergen is a glycoprotein. It is present in raw & roasted peanuts since it is heat stable. It may contaminate crude (cold pressed) peanut oil.
Sources of Peanut Allergens
Peanuts are widely used in Western & Oriental cooking.
Peanut, or traces, if present in a food, must be declared on the food label, even if peanut is not the primary ingredient.
Very good studies have shown that traces of peanut protein are found in cold pressed (crude) but not warm pressed peanut oils.
Peanut oil is sometimes called groundnut or arachis oil. Unfortunately manufacturers sometimes label foods as containing "vegetable oil" which may well contain peanut oil.
Avoid any foods, cosmetics, creams or ointments that contain or are made with Arachis oil. Some nipple creams used while breast feeding have been known to contain arachis oil, as do some ointments used to treat atopic eczema.
Other common sources of peanut include:
- Peanut, groundnut, arachis
- Peanut butter
- Baked goods – Pastry, biscuits, cookies, crackers, health bread
- Asian foods – Thai, Chinese & Indonesian dishes
- Vegetarian foods
- Cold pressed (crude) peanut oil
- Muesli and breakfast Cereals
- Ice creams
- Mixed Nuts, Marzipan
- "Natural" flavouring
- Egg rolls
- Health foods – bars & sweets
Diagnosis of Peanut Allergy
A history of an allergic reaction occurring shortly after exposure to peanuts is very suggestive. However, this should always be confirmed with a skin prick test or CAP RAST. There have been several cases where the wrong nut has been assumed, with serious consequences. Also, tree nuts should be tested in view of the frequent coexistence of these allergies.
DBPCFC is very rarely needed in peanut anaphylaxis. In doubtful cases or to confirm that the peanut allergy is outgrown (after borderline SPT or RAST) then it may be necessary.
Treatment of Peanut Allergy
If Anaphylaxis has occurred or in patients with previous immediate systemic reaction following peanuts (especially asthmatics) and when the CAP RAST is above the threshold level of 15kUa/l, all the precautions for Anaphylaxis should be taken.