Food hypersensitivity refers to both food allergy and food intolerance. See picture 1.
Rapidly developing urticaria and angio-oedema are common symptoms of food allergy. It is typical that the symptoms recur or persist and that they are clearly associated with eating.
Atopic eczema should be distinguished from food allergy. Mild eczema is rarely associated with food allergy, but in an infant with severe eczema foodstuffs may aggravate the eczema.
Suspected food allergy is at least 6 times more common than food allergy confirmed by challenge testing.
Reddening of the skin, baby reflux, loose stools or stools of different colours, excessive crying and restlessness often occur in infancy. These are common, benign and transient symptoms, and an underlying food allergy is often suspected as the cause.
The assessment concerning nutritionally essential foods (milk, cereals) is performed by a specialist. Elimination trials with foods that only cause mild symptoms and that are easy to avoid (e.g. strawberry, tomato, citrus fruit) can be carried out at home under guidance from health care personnel. If the child has difficult cutaneous or gastrointestinal symptoms or if respiratory symptoms or anaphylaxis is suspected, he/she is referred to a specialist.
An elimination diet started in infancy should either be timely stopped (at the age of 2 to 4 years in most cases) or proper grounds must be given for its continuation.
Dietary requirements in children starting school are checked by the school nurse. A special diet is only indicated if there have been significant symptoms of food allergy in a fresh challenge test.
Epidemiology
As many as half of all parents with children aged less than 1-2 years associate some of their child's symptoms with food; however, the majority of these suspicions rapidly disappear, usually within 6 months.
In a survey of school children, 24% reported to have, or to have had at some stage, a food allergy. The prevalence of food allergy in childhood is 2-6%.
In food allergy, an immunological mechanism has been demonstrated in addition to the symptoms, either by determining food specific IgE antibodies in the serum or with a skin prick test.
Prevention
No measures with a preventative effect are available for food allergy.
There are conflicting results as regards the effect of breastfeeding on the development of atopic disease and food allergy. Exclusive breastfeeding for 4-6 months is recommended, but there is no clear evidence that it would reduce the risk of allergy in the child. Widening the diet and versatile use of solid foods has in many studies enhanced the development of food tolerance also in children with eczema and with reactions to IgE tests.
Any food that contains proteins can cause allergy. Genetic predisposition to allergies increases the risk. The environmental factors that increase the risk of allergy or that protect from developing allergy are not well known on the individual level.
Cow's milk, wheat and egg allergy
Milk, wheat and egg are important causative agents in infants and small children.
Rarely seen after pre-school age
Symptoms caused by these nutritionally important foods appear in infancy a few weeks after the food has been introduced to the child's diet.
The diagnosis should be confirmed with a supervised elimination-challenge test conducted in specialized health care.
Different plant allergens share a similar structure with birch pollen, and consequently, when eaten, many fresh fruits, vegetables and nuts cause itching of the lips, oral mucosa, throat and ears, as well as erythema and urticaria in the skin through direct contact in those with pollen allergy.
Tree nuts (e.g. hazel nuts and walnuts), peanuts (belonging to leguminous plantstogether with pea and soya) and almonds are common causes of symptoms. Raw root vegetables such as potato, carrot, celery and parsnip, and fruit with or without stone, such as apple, pear, peach, cherry, kiwi fruit, plum and mango, often cause symptoms. Spices can also cause symptoms, including mustard, caraway, turmeric, ginger and cinnamon. Many patients only get symptoms during the pollen season.
Preparation of fruit and vegetables (cooking and freezing) removes their allergenicity making it possible for those allergic to birch pollen to consume them.
Foods that cause symptoms are avoided according to symptom emergence. Due to cross-reactions, positive results are very common in skin prick and specific IgE antibody tests, but they correlate poorly with the symptoms. Therefore, testing is not recommended.
Food intolerance
Enzyme deficiency
The most common form is lactase deficiency, which leads to lactose intolerance. The symptoms usually emerge at school age or in adulthood.
Biogenic amines that release histamine
Strawberry, citrus fruit, chocolate, tomato
Anaphylactic reaction
In theory, any food can act as the causative agent.
In children: milk, wheat, egg, nuts, seeds
In adults: nuts, seeds, shellfish, and fish
The patient is referred to specialized care for further assessment and the reaction is appropriately recorded.
Essential questions
Signs and symptoms: what were the observed symptoms and when did they start, and have the symptoms recurred? What was the timing of the onset of symptoms in relation to food exposure? Strength of the symptoms?
Current diet; has some food already been eliminated and what are the reasons for the elimination?
Atopic eczema; what skin care methods have been used (moisturising lotions, emollients, topical glucocorticoids)?
Breastfeeding (duration of exclusive breastfeeding, total duration of breastfeeding), the first contact with infant formulas, introduction of complementary foods, any particular maternal diets
Family history of allergies
Smoking
Could the patient have a metabolic disorder, coeliac disease or lactose intolerance?Courses of antimicrobials (effect on intestinal symptoms)?
Growth chart (height, weight, head circumference)
Infant (< 1 year)
History
Do symptoms warrant further investigations or are they part of normal infancy? Infants are individual and their temperaments vary, which is reflected in the child's contentment, happiness, crying and sleep-wake pattern.
The consideration of confounding factors is particularly important.
Atopic eczema usually appears in infancy at the same time as new foods are tried, and the possibility of misinterpretation is great.
If a nutritionally essential or otherwise common foodstuff (cow's milk, cereals, egg) repeatedly causes significant and similar symptoms, it may be eliminated as a trial for a period of one week during which time the symptoms are followed. The matter should be investigated properly with the support of health care personnel.
Any food elimination that has no effect on the symptoms must be discontinued without delay.
An older child
Food-induced symptoms are unlikely
Cross reactions in birch pollen allergy: see above
A rash that heals in the summer is not caused by food allergy.
Symptoms of food allergy
Cutaneous manifestations
Urticaria and redness of the skin (immediate reactions), exacerbation of atopic eczema (delayed reaction and rarely the only symptom of food allergy)
Atopic dermatitis is a chronic inflammatory skin disease, and its underlying causes include heredity, environmental factors and disturbed penetration of the skin. A food substance is often found to be an exacerbating factor in severe atopic eczema in an infant.
Atopic dermatitis may be exacerbated by many factors, including dry winter air, stress, infections and sweating, as well as mechanical and chemical irritation. The relapsing-remitting nature of the disease is typical of the disease, which is challenging in infancy when many new foods are introduced.
Intestinal symptoms
Vomiting, changes in stool consistency, persistent crying and restlessness are very difficult to interpret in an infant. The frequency of bowel motions varies greatly between individuals. For example, a normal pattern for an infant may be a bowel movement 10 times a day or once a week (provided that the child is well and developing normally).
All changes in the diet can cause temporary changes in bowel function, which is a normal phenomenon.
Of gastrointestinal symptoms, the most obvious one is contact allergy around the mouth and lips which appears almost immediately after ingestion and is therefore easy to connect with the offending food (tomato, citrus fruit and apple in birch pollen allergy).
Respiratory tract symptoms
Rhinitis, itchy eyes, sneezing and dyspnoea are rare.
They are usually associated with a severe systemic reaction with signs of urticaria and anaphylaxis.
Symptom timing and other symptoms
IgE-mediated symptoms usually occur within minutes and no later than within 1-2 hours. Delayed symptoms occur within hours.
It is extremely difficult to associate delayed intestinal reactions, excessive crying, restlessness and exacerbations of atopic eczema with a particular food. A double-blind food challenge may be of use in the diagnosis.
Diagnosis of food allergy
Elimination and challenge tests form the basis of diagnosis (picture 2) Cow's Milk Allergy. For nutritionally important foods (milk and wheat in young children) an elimination-challenge test is carried out under physician supervision in specialized care or in the surgery e.g. according to the instructions below.
The suspected food(s) is totally eliminated from the diet (for 1-2 weeks).
The development/resolution of symptoms is recorded in a symptom diary.
Disappearance of symptoms supports the presence of food allergy, but it is not diagnostic. The food needs to be reintroduced.
A small amount of the food is introduced to the diet and as long as the child remains asymptomatic the amount is increased gradually to the normal (age-adjusted) daily amount. Find out about local challenge protocols. See also the article on cow's milk allergy Cow's Milk Allergy. Challenge of only a short duration is usually sufficient if, based on patient history, there is a suspicion that immediate symptoms such as urticaria and angio-oedema may appear. If delayed symptoms are suspected, the challenge is continued at home for a few days with the initially defined portions and then with age-appropriate portions until symptoms appear or the food is kept in the diet.
Immediate symptoms usually appear within minutes or within an hour. Delayed symptoms appear in 1-2 days following the reintroduction of the food (symptom diary), provided that the amounts consumed are adequate.
Tests of nutritionally less important foods that only cause mild symptoms can be carried out at home under parental supervision.
Suspicion of anaphylactic reactions caused by food: the situation is assessed in specialized care.
Allergy tests
IgE tests (specific IgE, skin prick tests) should not be used in the investigation of mild symptoms that are treated in the primary care.
In children with more severe symptoms, specific IgE tests targeted according to the patient history are carried out in specialized care.
IgE tests are not diagnostic.
As a basic rule, IgE testing of older children for foodstuffs should be avoided unless there is a strong suspicion or symptom.
Pre-school and older children can typically have positive results to skin prick and specific IgE tests, which are of no clinical significance.
Allergen component testing with IgE antibodies is a diagnostic method which is used to assess whether the child has cross reactivity with pollen proteins or a real nut allergy, and how severe is the allergy.
IgA and IgG antibodies only tell that the child has been in contact with the food in question and they are not useful in diagnostics.
Epicutaneous testing is according to current knowledge not a reliable diagnostic method.
Treatment
Food allergy is treated by avoiding the symptom-generating food for a specified period of time. The extent of avoidance depends on the severity of the symptoms; if the symptoms are mild there is no need to totally eliminate the offending food, which may hasten the development of tolerance. Otherwise, a normal age-appropriate diet is provided.
If nutritionally important foods (milk, cereals) are to be eliminated, it must be ensured that alternative nutrients are provided, and a dietitian should be involved in the care.
Normal growth and development of a child on a special diet has to be taken care of.
The mother to a child with food allergy can usually follow normal diet during breastfeeding.
Prognosis
Early childhood food allergies resolve quickly. Half of children with cow's milk allergy will tolerate milk at the age of 2 years and 75% at the age of 3 years. Cereal and egg allergies also resolve in the majority of children by the time they reach school age at the latest.
Follow-up and organisation of care
Individual foods which are of no nutritional significance can be eliminated in primary care if the causal relationship of food to symptoms is clear and the symptom is significant. Elimination and reintroduction can be carried out at home whilst keeping a symptom diary. Rechallenging is to be encouraged.
Clinical experience dictates the follow up routines.
Indications for a referral to a specialist
A small infant with widespread or worsening eczema
A small infant with difficult or perplexing symptoms, and the parents are convinced of food allergy
An infant in whom food allergy to an important nutrient is suspected (milk, wheat)
Failure to thrive
Barren diet
Suspicion of anaphylaxis
In primary care
The growth of a child on an elimination diet is monitored with growth charts.
Vaccinations are given according to the normal programme. Allergy to egg does not prevent vaccination unless the child has had an anaphylactic reaction to egg Vaccinations.
The family is encouraged to expand the diet towards a normal diet.
The child's diet should be regularly (annually) re-evaluated during the visits to the child health clinic: is the avoidance of certain foods based on an elimination-challenge test? Should a specialist re-evaluate the situation?
In Finland, one of the aims of the National allergy program (2008-2018) was to increase the tolerance of the population against allergens, and as a result, the number of special diets in daycare centres and schools was decreased by half http://www.jacionline.org/article/S0091-6749(21)00559-5/fulltext.
References
Hoare C, Li Wan Po A, Williams H. Systematic review of treatments for atopic eczema. Health Technol Assess 2000;4(37):1-191. [PubMed]
Johansson SG, Hourihane JO, Bousquet J, Bruijnzeel-Koomen C, Dreborg S, Haahtela T, Kowalski ML, Mygind N, Ring J, van Cauwenberge P, van Hage-Hamsten M, Wüthrich B, EAACI (the European Academy of Allergology and Cinical Immunology) nomenclature task force. A revised nomenclature for allergy. An EAACI position statement from the EAACI nomenclature task force. Allergy 2001 Sep;56(9):813-24. [PubMed]
Eggesbø M, Halvorsen R, Tambs K, Botten G. Prevalence of parentally perceived adverse reactions to food in young children. Pediatr Allergy Immunol 1999 May;10(2):122-32. [PubMed]
Venter C, Pereira B, Grundy J, Clayton CB, Roberts G, Higgins B, Dean T. Incidence of parentally reported and clinically diagnosed food hypersensitivity in the first year of life. J Allergy Clin Immunol 2006 May;117(5):1118-24. [PubMed]
Csonka P, Kaila M, Laippala P, Kuusela AL, Ashorn P. Wheezing in early life and asthma at school age: predictors of symptom persistence. Pediatr Allergy Immunol 2000 Nov;11(4):225-9. [PubMed]
Greer FR, Sicherer SH, Burks AW, American Academy of Pediatrics Committee on Nutrition, American Academy of Pediatrics Section on Allergy and Immunology. Effects of early nutritional interventions on the development of atopic disease in infants and children: the role of maternal dietary restriction, breastfeeding, timing of introduction of complementary foods, and hydrolyzed formulas. Pediatrics 2008 Jan;121(1):183-91. [PubMed]
Høst A, Halken S, Muraro A et al.. Dietary prevention of allergic diseases in infants and small children. Pediatr Allergy Immunol 2008 Feb;19(1):1-4. [PubMed]
Lee J, Seto D, Bielory L. Meta-analysis of clinical trials of probiotics for prevention and treatment of pediatric atopic dermatitis. J Allergy Clin Immunol 2008 Jan;121(1):116-121.e11. [PubMed]
Kukkonen K, Savilahti E, Haahtela T, Juntunen-Backman K, Korpela R, Poussa T, Tuure T, Kuitunen M. Probiotics and prebiotic galacto-oligosaccharides in the prevention of allergic diseases: a randomized, double-blind, placebo-controlled trial. J Allergy Clin Immunol 2007 Jan;119(1):192-8. [PubMed]
Räsänen L, Ylönen K. Food consumption and nutrient intake of one- to two-year-old Finnish children. Acta Paediatr 1992 Jan;81(1):7-11. [PubMed]
Vandenplas Y, Koletzko S, Isolauri E, Hill D, Oranje AP, Brueton M, Staiano A, Dupont C. Guidelines for the diagnosis and management of cow's milk protein allergy in infants. Arch Dis Child 2007 Oct;92(10):902-8. [PubMed]
Wickens K, Black P, Stanley TV et al. A protective effect of Lactobacillus rhamnosus HN001 against eczema in the first 2 years of life persists to age 4 years. Clin Exp Allergy 2012;42(7):1071-9. [PubMed]
Vetander M, Helander D, Flodström C et al. Anaphylaxis and reactions to foods in children--a population-based case study of emergency department visits. Clin Exp Allergy 2012;42(4):568-77. [PubMed]
Moneret-Vautrin DA, Morisset M, Flabbee J et al. Epidemiology of life-threatening and lethal anaphylaxis: a review. Allergy 2005;60(4):443-51. [PubMed]
Nwaru BI, Hickstein L, Panesar SS et al. The epidemiology of food allergy in Europe: a systematic review and meta-analysis. Allergy 2014;69(1):62-75. [PubMed]
Nwaru BI, Takkinen HM, Niemelä O et al. Timing of infant feeding in relation to childhood asthma and allergic diseases. J Allergy Clin Immunol 2013;131(1):78-86. [PubMed]
Nwaru BI, Takkinen HM, Kaila M et al. Food diversity in infancy and the risk of childhood asthma and allergies. J Allergy Clin Immunol 2014;133(4):1084-91. [PubMed]