Allergy to peanuts and tree nuts usually occurs in pre-school children. The cumulative prevalence of peanut allergy in the UK is 0.7 -1.4%, and peanut allergic individuals have a 25–40% risk of developing a co-allergy to tree nuts. Challenge-confirmed tree nut allergy is under 2%, with hazelnut being the most common tree nut allergy in Europe, although in the UK other nuts such as almond walnut and Brazil nut might be more relevant. Cashew nut, the main nut allergen in USA and Australia, is an increasingly common cause of nut allergy in the UK and can cause severe reactions. Although peanut can cause severe reactions, 40% of severe reactions to nuts are due to tree nuts. Although nut allergies most often commence in childhood, adults can develop new-onset allergy to peanuts and tree nuts, including Macadamia nuts, Brazil nuts and cashew nuts. However adults most often report reactions to nuts due to pollen-related cross-reactivity.
Although peanut and tree nut allergy is often considered to be lifelong, up to 40% of those with a peanut allergy might experience resolution. Also 30-40% of those with a peanut allergy will tolerate some tree nuts. Thus it is important to determine which nuts could be tolerated and included into the diet, especially since strict avoidance of peanuts has been associated with increased anxiety.
The avoidance of peanuts and tree nuts is facilitated by the requirement of labelling laws to declare added nuts, but advisory labelling is difficult to interpret. Peanut allergens can persist in saliva and on household surfaces which means accidental exposure is a real possibility, with reactions to peanuts reported to affect just under 5% of individuals after they had been diagnosed with a peanut allergy. More than half of anaphylaxis fatalities have occurred when eating restaurant or takeaway food, also those with asthma are more likely to have severe reactions. For these reasons adrenaline (epinephrine) is often prescribed for peanut and/or tree nut allergic individuals.
For diagnostic purposes, in young children with no pollen sensitisaiton and convincing symptoms, a SPT/SIgE to the relevant nut is recommended. For older children and adults, especially those sensitised to tree, grass or weed pollens, CRD assessing sensitisaiton to the major allergens in peanuts and tree nuts is useful. Symptom history needs to be interpreted with test results and algorithms to determine whether the patient has a nut allergy or PFS. In turn this will inform the decision as to whether the patient requires an AAI.
Seeds are becoming an increasing part of the UK diet, and sesame is the most prevalent seed allergy which usually presents in early childhood, although it can also present as a new adult-onset food allergy. Sesame seeds can provoke anaphylaxis, and this has been linked to the allergens in the oil-bearing part of the seed. The incidence of sesame allergy is greater in those who are peanut and tree nut allergic. It is thought only 20% of children with a sesame allergy are likely to experience resolution. Other seeds which have been linked to allergy include sunflower seed, pumpkin seed and mustard seed.