Nut allergy

Tree nuts such as walnuts, hazelnuts, almonds, cashews, pecans, macadamias, brazils and pistachios can act as allergens and cause an allergic reaction in some people.  However the most widely documented nut allergy is to peanuts.  Peanuts aren’t actually a true nut they are a legume and grow underground.  The proteins in peanuts are similar in structure to those in tree nuts and therefore people who are allergic to peanuts can also be allergic to tree nuts.  It is important therefore to avoid all nuts if you have a nut allergy.  The allergic reactions to both tree nuts and peanuts will tend to be the same. 

A nut allergy can develop at any age although it is most predominantly found in children.  First allergic reactions tend to take place between the ages of 14 months and two years old and will occur when you first come into contact with nuts.  Your immune system will react and prepare to fight although in the first instance you don’t get any symptoms of a reaction.  It is only when you come into contact with nuts for a second time that a full allergic reaction happens.  Many children will appear to have a reaction when they are first exposed to nuts.  This is likely, however, to be their second exposure since they may well have already had exposure to nuts through their mother either when in the womb or through breast feeding.   Unlike some other allergies an allergy to nuts will generally last a lifetime.

Reactions to nuts will vary from mild to severe and can sometimes be life threatening.  Many people will react after contact with small amounts (less than one nut) and some people may react to trace amounts.  In these instances a nut doesn’t even need to be eaten; a reaction can be caused by just having a tiny amount on the lips or by standing next to someone eating nuts.  Symptoms will usually start quickly with some people reacting within minutes.

A mild reaction will generally consist of one or more of the following symptoms:

• Tingling mouth and lips
• Face swelling
• Feeling sick
• Hives
• Abdomen pains
• Tightness around the throat

A severe reaction can lead to an anaphylactic shock where the symptoms will include the symptoms above along with wheezing or difficulties breathing, feeling faint and a fast heart rate.  It is therefore important for those people who are likely to have a severe reaction to carry an injectable epinephrine (such as an EpiPen or Anapen) around with them.

A nut allergy can be diagnosed by seeing your doctor or health professional who can carry out one of the following tests:

Skin Prick Test – a small drop of nut extract solution is placed on your forearm.  A needle prick is then made through the drop.  A positive reaction, showing an allergy, will occur within 20-30 minutes with the skin under the solution becoming red and itchy.  A white, raised swelling (a weal) will then appear surrounding the red central area.   It will take 15-20 minutes to reach full size and then fades over the following few hours.  It is important that no antihistamines are taken prior to the test since this is likely to affect the allergic response during the test.

Blood test – A blood test (RAST) will measure the amount of IgE which is produced as a result of an allergic reaction.

Food Challenge – If the above tests are inconclusive it may be necessary to take part in a food challenge test.  Food will be consumed which may or may not contain nuts.  Observation will be given over the following 15-30 minutes to see if there is any reaction.  A food challenge will always be administered in a hospital in case of any severe reactions.

There is no treatment for a nut allergy apart from avoiding peanuts and tree nuts.  This does not just mean not eating nuts but ensuring that any food consumed does not contain nuts as an ingredient and avoiding cross contamination when preparing food.  It is important to check all food labels for phrases, such as:

• May contain nuts
• Produced on shared equipment with nuts or peanuts
• Produced in a facility that also processes nuts

If you suspect a nut allergy you must speak with your doctor and if this is confirmed notification of the allergy should be made to schools, family and friends.

Information written by the talkhealth medical panel

Last Reviewed: 10 February 2011
Next Review Date: 18 October 2012