The Hygiene Hypothesis -- Redefine, Rename, or Just Clean It Up?

Linda Brookes, MSc; Laurence E. Cheng, MD, PhD


April 06, 2015

In This Article

What Is the Best Advice for Preventing Allergies in Young Children?

"In terms of lifestyle changes, unless prospective parents go live on a farm and you regularly come into contact with animals, at this point there are no other data to suggest that any change in lifestyle will be of benefit [in preventing allergies]," Dr Cheng admitted. "The science has been very well done, but in the lay sense, the hygiene hypothesis has been interpreted as, 'We should therefore be putting our kids into dirt, exposing children to manure,' etc. We have come a long way in lowering infant mortality, and we don't want to throw the baby out with the bath water, so I would not agree that somehow people should be less clean." He stressed the need for more research: "Before we go there, we need to understand what is wrong and how it is wrong, and that is the power of basic science."

In cases of food allergies, Dr Cheng suggests that referral to an allergist might be appropriate for high-risk children, such as those enrolled in the LEAP study, who had severe eczema, food (egg) allergy, or both. "I want to be clear that the study had a narrow definition of children who were included in the study. The patients had to meet study-defined eczema activity and/or food allergy," he emphasized.

Severe eczema in this study was defined as:

  • A rash that required the application of topical creams and ointments containing corticosteroids or calcineurin inhibitors and, if the participant is:

    • Younger than 6 months of age, lasted for at least 12 out of 30 days on two occasions; or

    • Older than6 months of age, lasted for at least 12 out of 30 days on two occasions in the last 6 months; or

  • "A very bad rash in joints and creases" or "a very bad itchy, dry, oozing, or crusted rash," as described by the participant's parent or guardian in a pre-enrollment questionnaire; or

  • A rash that is currently or was previously graded 40 or higher using the modified SCORAD evaluation.

He also cautioned about misdiagnosis of food allergy, which in a recent study could be as high as 89% of children who had undergone a food blood test panel.[24] "Sensitization does not equal a clinical allergy diagnosis," he said. "That is why there is confusion, and that is why it has been somewhat overdiagnosed—because people test positive for these allergens, but in fact some of them are eating those foods and yet not having any issues." He cited a study of National Health and Nutrition Examination Survey (NHANES) data that concluded that a large percentage of people with high food-specific immunoglobulin E levels in the blood are eating the foods without a problem and so do not have true clinical allergy.[25] "People can have very high levels and yet if they are eating the food and tolerating it, by definition they are not allergic, no matter what the tests say," he said. Instead, these tests only corroborate the key clinical findings in patients with allergy. "Usually the immune response resulting in allergy is very stereotyped. Children get hives, diarrhea, vomiting, or difficulty breathing," he explained. New US guidelines for the prevention of environmental allergies and asthma and food allergies in children are under development. Dr Cheng hopes to see these new guidelines within the next 2 years, if not sooner. An additional consideration moving forward will be to find safe and developmentally appropriate vehicles for foods introduced in younger infants.


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