The role of food allergy in atopic dermatitis, which has never been in doubt amongst
practising Allergists, has been the source of more controversy than any other subject
matter amongst dermatologists. Some of the confusion arises from dermatologists
who assume that because atopics will have several positive IgE-mediated reactions
to foods and inhalants, "it is not possible to make a definitive diagnosis
of clinically relevant food allergy". Every clinician treating infants
with atopic dermatitis successfully will agree that a significant proportion of
these kids with severe eczema will be found to have a relevant food allergy, if
it is looked for.
Several published prospective studies have determined the incidence of the common
food allergies in children as:
- Cow's milk: 2.5%
- Eggs: 2%
- Peanuts: 0.5 – 0.7%
Cow's milk allergy / intolerance & atopic dermatitis (AD) in infancy & childhood
Symptoms suggestive of CMPA/CMPI are seen in about 5-15% of infants, but the "true
incidence" ranges from 2% to 3%, when the strict diagnostic criteria are used
Adverse reaction to cow's milk should be the term used to describe cow's milk protein
allergy (CMPA) & cow's milk protein intolerance (CMPI), because no differentiation
is possible on the basis of symptoms, and there is no reliable single lab test available
for the diagnosis of CMPA or CMPI.
Approximately one third of AD children have a diagnosis of CMPA/CMPI according to
elimination diet and challenge tests, and about 40-50% of children <1 year of
age with CMPA/CMPI have AD.
CMPA/CMPI may induce a diverse range of symptoms including:
- Skin (most common) – AD, urticaria, angioedema (swelling of various body parts)
- Respiratory – rhinitis, asthma, cough
- Gastrointestinal – vomiting, diarrhoea, colic, gastroesophageal reflux
- Non-specific – failure to thrive, irritability.
AD is the most common skin manifestation of CMPA/CMPI.
AD is a chronic inflammatory disease in which the individual's genes, environment,
psychic, immune system and drug therapy contributes to its severity.
Immunologic findings include:
- Increased IgE
- Increased eosinophils
- Increased spontaneous histamine release from mast cells
- Increased IL-4 and Il-5 secreting Th2 cells
- Decreased numbers of interferon-gamma secreting Th1 cells.
Koch's postulate of causality in AD
Over the past 2 decades several studies have fulfilled Koch's postulate of causality:
- Removal of causative agent leads to resolution
- Introduction of causative agent leads to the disease
- Avoidance of the causative agent leads to prevention of the disease.
In studies in children with food-related AD where oral controlled food challenges
were used (2,3) skin reactions occurred in three fourths of the positive challenges
and consisted of itchy, measles-like or flat red lesions in the usually affected
sites of AD.
Most of the reactions occurred within an hour after beginning the oral challenge.
Eggs, milk and peanut were the most common foods responsible for the reactions.
Milk-induced reactions were 10-40% of the positive response (2).
Prognosis of food Allergy in infants with atopic dermatitis
Most food allergy is acquired in the first one to two years of life. The prevalence
of food allergy peaks at 5% – 8% at one year of age and then falls progressively
until late childhood, after which the prevalence remains stable at 1- 2%.
Most food allergy is indeed lost over time. It is therefore not surprising that
dermatologists treating only adults with atopic dermatitis will see relatively few
with food allergy. In a prospective study by Bock (6) almost all of the adverse
reactions had been lost by the age of three years. Among these, there were 11 children
with confirmed milk allergy, all of whom were able to tolerate
milk by the age of three. The median duration of adverse reactions to milk was only
Egg Allergy – All the studies looking at egg allergy in infancy
shows that the vast majority of egg allergy is also outgrown by the school-age years.
Peanut Allergy – Peanut allergy is likely to be lifelong
for most but not all patients. About 20% of children with peanut allergy will outgrow
their allergy. The more severe the allergy the least likely it is to be out-grown.
Important studies from around the world linking AD with foods
Atopic Dermatitis and food Hypersensitivity reactions
Burks AW; James JM et al, Dept. Paediatrics, Univ. Arkansas, Little Rock, USA
Paediatrics, 132(1): 132-6 1998 Jan
Objective: To determine the role of food hypersensitivity in atopic
dermatitis and to determine whether patients with atopic dermatitis who had food
hypersensitivity could be identified by screening prick skin tests using a limited
number of food allergens.
Study Design: Patients with atopic dermatitis attending Arkansas
Children's Hospital Paed. Allergy Clinic underwent allergy skin prick testing to
a battery of food allergens. Patients with positive skin prick tests underwent double-blind,
placebo-controlled food challenges.
Results: 165 patients were enrolled and completed the study. Patients
ranged in age from 4 months to 21.9 years (mean 48.9 months). 98 (60%) of the children
had at least 1 positive prick test. A total of 266 DBPC food challenges were performed.
64 children (38.7% of total) were interpreted as having a positive challenge.
(milk, egg, peanut, soy, wheat, fish, and cashew) accounted
for 89% of the positive challenges. By use of screening prick skin tests of these
7 foods we could identify 99% of the food allergic patients correctly.
Conclusion: This study confirms that most children with atopic
dermatitis have food allergy that can be diagnosed by a skin prick test for the
The incidence of food allergy in atopic dermatitis
Ogura Y, Ogura H, Zusi N., Dept of Clinical Research & Paed Allergy, Kochi National
Arerugi 2001 Jul; 50(7): 621-8
To clarify the incidence of food allergy in atopic dermatitis, 226 non-selected
cases with AD attending their hospital were evaluated by oral food challenges based
on masked food challenges.
181 of 200 cases (26 cases dropped out) showed a positive reaction to at least one
In conclusion, the incidence of food allergy in AD was 90.5%, and
egg allergy, cow's milk allergy, soy bean allergy, wheat allergy, rice allergy were
83.5%, 51.5%, 33.5%, 20.0%, 2.5% respectively in the 200 cases.
The association of atopic dermatitis in infancy with IgE-mediated food sensitisation
Hill DJ, Sporik R, Thorburn J, Hosking CS, Dept. Allergy, Royal Children's Hosp.,
J Paediatrics 2000 Oct; 137(4): 475-479
Objective: To prospectively investigate the association of high
levels of IgE sensitisation to foods and the presence of AD (judged by reported
topical steroid use during the first 16 months of life) in a birth cohort of 620
Australian children "at risk" of allergic disease because of family history.
Results: A total of 559 of the children in the cohort were fully
evaluated, and the cumulative prevalence of AD was 24%. More children in the cohort
who had AD had strongly positive skin test results, consistent with IgE sensitization
to either cow's milk, egg, or peanut at 6 months (22% vs 5%, and at 12 months 36%
vs 11%) than those without AD. The calculated attributable risk percent for IgE
food sensitisation as a cause of AD was 65% and 64% at these times. In a separate
group of infants with severe AD, the equivalent rates of IgE food sensitisation
at 6 months were 83% and at 12 months, 65%.
Conclusion: IgE food sensitisation is a major risk factor for the
presence of AD in infancy.
Evidence that Atopic Dermatitis is part of a systemic TH2 disease (Atopy), which
also includes asthma and allergic rhinitis:
- Patients with AD have elevated total IgE level and specific IgE (CAP – RAST)
- Nearly 80% of children with AD eventually go on to have asthma or allergic rhinitis.
When mice are sensitised through the skin with protein antigen, it induces a localised
allergic dermatitis, elevated serum IgE, airway eosinophilia, and hyperresponsiveness
to methacholine, suggesting that the skin exposure to allergen in AD may enhance
the development of allergic asthma.
Laboratory correlates of AD & Food Allergy
- AD associated with elevated food specific IgE antibodies
Ingested food proteins can trigger skin mast cells (Walzer, J Immunol 1927)
- AD with food allergy have GI malabsorption
Plasma histamine rises during positive food challenges (Sampson et al NEMJ 1984)
Eosinophils are activated when causal foods are being ingested
J Roy Soc Med 1997;
90 (S30): 3-9]
Diagnosis of food allergy in atopic dermatitis
The value of skin prick tests (SPT) in diagnosis of food allergy in AD
From a study published by Sporik et al. Clin Exp Allergy 2000; 30:1540-1646, the
size of the SPT wheal can predict with 100% accuracy that the open food challenge
will be positive.
Children: 0-2 years of age
Children: all ages (median=3 yrs)
Value of specific IgE antibody (CAP-RAST) in the diagnosis of food allergy
Recently, new developments in the lab (in-vitro) diagnostics for IgE-mediated food
allergies have occurred. Correlating food allergen-specific IgE concentrations in
the serum (Immuno-CAP RAST) and skin prick test wheal diameters with patient histories
and outcome of DBPCFC diagnostic decision points have been established
for peanut, egg, milk and fish.
Diagnostic decision points that are 90% to 100% predictive of clinical reactivity
to common food allergens.
(Hugh Sampson) JACI 2001; 107: 891-896
Atopy Patch Test (APT) (4)
Recently, the atopy patch test (APT) has been used to supplement the skin prick
test in the diagnosis of food allergy in children with atopic eczema. These tests
are particularly useful in investigating delayed reactions to milk and improves
the accuracy of skin prick tests, since about half of the reactions following the
ingestion of milk are not mediated by specific IgE antibodies to milk protein (delayed
Food allergy and atopic eczema are both common diseases in infancy. Atopic eczema
"is a complex disease with many triggers, foods being very important and often
missed in infancy". From the very good studies carried out in recent years,
showing clear causality between foods and eczema in infants, it is time for egos
and emotions to give way to rationality.
(1) Host A & Halken S. Epidemiology and prevention of cow's milk allergy.
1998;56 (suppl 45): 111-113
(2) Sampson HA & McCaskill CC. Food Hypersensitivity and atopic dermatitis:
evaluation of 113 patients.
J Pediatrics 1985;56: 669-675
(3) Burks AW, James JM et al. Atopic dermatitis and food hypersensitivity reactions.
J Paediatrics 1998;56: 132-136
(4) Niggeman B, Reibel S and Whan U. The atopy patch test (APT) – a useful
tool for diagnosis of food allergy in children with atopic dermatitis.
(5) Host A. Cow's milk protein allergy and intolerance in infancy: some clinical,
epidemiological and immunological aspects.
Paediatr Allergy Immunol 1994;56:
(6) Bock SA. Prospective appraisal of complaints of adverse reactions to foods in
children during the first 3 years of life. Pediatrics 1987:79:683-8.