The number of children who suffer severe, systemic allergic reactions is rising. This increase in prevalence in recent years is likely to be caused by a number of factors, and further research is needed to determine what they are. Any food containing protein can cause an allergic reaction, but in reality most reactions are caused by a small number of foods. These include cow's milk, egg, peanuts, tree nuts, sesame, fish and shellfish.
There has been much speculation that babies in families prone to allergies may become sensitised while they are in the womb, or through their mother's breast milk. It is now known that a foetus can recognise allergens to which the mother is exposed as early as the second trimester of pregnancy (3-6 months). In addition, allergens have been found in the breast milk of lactating mothers. In response to this information, the Department of Health issued guidelines to women in 1998, suggesting that they "may wish" to avoid nuts and peanuts during pregnancy and while breastfeeding if there is allergy in the immediate family (i.e. if they or their partners are allergic, or if they have an allergic child, e.g. with asthma, eczema, hay fever or food allergy).
However, research in this field is incomplete. Although the Government guidelines still stand, no studies have yet shown conclusively that avoiding dietary allergens during pregnancy and lactation reduces the incidence of allergic disease in children.
Many families are understandably worried about how they can protect their children from developing allergies and there is often particular concern in families where there is already a history of atopy. Although more research is needed to answer the many questions surrounding sensitisation, some of the following strategies could help, whether there is atopy in the family or not:
In March 2003, researchers looking at the causes of peanut allergy among children identified two possible explanations.
They found that sensitisation may occur when skin preparations containing tiny amounts of peanut protein are applied to young children with eczema. In eczema the skin barrier breaks down and there is an abundance of immune cells in the skin that could be exposed to substances that cause allergies.
A second possible cause is exposure to soy formulae during infancy. Soya and peanut belong to the same family of legumes and have related proteins. The theory is that children exposed to soy formulae may become sensitised to peanut.
The researchers, commissioned by the Government's Food Standards Agency, were investigating risk factors for the development of peanut allergy in children in the UK. They identified children with peanut allergy in a large birth cohort of children in the southwest of the UK (Avon Longitudinal Study of Parents and Children – ALSPAC).
The ALSPAC study found that peanut allergy commonly occurs in children who have suffered eczema and rashes in early infancy. The chances of developing peanut allergy are increased if the rash is more severe with oozing and crusting. The authors found that applying preparations containing arachis oil (peanut oil) to the skin of infants with rashes was associated with an increased risk of developing peanut allergy.
Although the peanut oil present in skin preparations will have been refined, even refined oils are likely to contain minute amounts of protein. These may be hydrophobic proteins, which stay bound to fat and which may be difficult to detect.
Dr Gideon Lack, who led the study, said: "My own view is that infants with inflammatory conditions should not be prescribed creams or ointments containing peanut or nut oils. However, patients must not stop any medications for eczema without first consulting with their GP or specialist."
Additionally, the ALSPAC study found that significantly more infants who developed peanut allergy had been exposed to soya formulae during infancy. They acknowledge that the connection may in fact represent an association rather than a cause. Children who are placed on soya infant formulae are usually the ones who have eczema or milk allergy and therefore the reason they develop peanut allergy may simply be a reflection of the fact that they are atopic children. Although a statistical analysis suggested that soya exposure may actually have a causal role, the team acknowledge that their findings were inconclusive. Further research is needed.
Dr Lack says: "I personally would not recommend soya as a first line alternative to cow's milk formulae in children with a family history of atopy."
However, he acknowledges that soya is a useful alternative formula in certain groups of children with cow's milk allergy. The physician needs to balance the potential benefits against the possible risks, on an individual basis.
The researchers were unable to make a statement about the hypothesis that maternal consumption of peanuts during pregnancy or breast feeding may lead to the development of peanut allergy. Although they could find no link, they acknowledge that neither possibility can yet be ruled out.
Every effort has been made to ensure that the information provided above is accurate and helpful. However, it must be remembered that further investigation into allergic sensitisation is needed in order to affirm and/or clarify the research on which this information sheet is based.
Acknowledgements:This information was written by the Anaphylaxis Campaign with help from Prof John Warner, Professor of Child Health at the University of Southampton; Dr Gideon Lack, Consultant in Paediatric Allergy and Immunology at St Mary's Hospital, Paddington, London; Kate Grimshaw, Research Dietitian into Food Allergy at Southampton University; and Sue Clarke, Senior Child and Family Nurse for South Cambs PCT.