By Dr. Paul Ehrlich
For families caught between the rock of a peanut-allergy patient and the hard place of others who love their peanuts, the job of housekeeping got quite a bit harder this week with the publication of two articles in the Journal of Allergy and Clinical Immunology by a group of British researchers. One is called “Distribution of peanut protein in the home environment”. The team “sought to validate a method to quantify environmental peanut exposure, to determine how peanut is transferred into the environment after peanut consumption, and to determine whether environmental peanut persists despite cleaning.” They found, “Peanut protein persisted on hands and in saliva 3 hours after peanut consumption. Peanut protein was completely removed from granite tables after cleaning with detergent, and levels were reduced but still present after detergent cleaning of laminate and wooden table surfaces, pillows, and sofa covers.”
The one bright spot for peanut fans is that except for the air directly above active peanuts shelling, the dust doesn’t waft around the room, and airborne traces couldn’t meet the threshold for registering on the tests. However, hands and mouths make ideal conveyances in the interval between eating and intensive washing.
The other study sought to measure the level of biological activity in the peanut residue via a basophil activation assay. That is, peanut dust samples taken from bedding and play areas were added to peanut-sensitized effector cells to create an in vitro allergic reaction.
These were highly worthy studies, undertaken at a time when more and more evidence is accumulating that food-allergy sensitization comes not via ingestion but through infant skin. We had an item on our New Science page a few months ago about a study (click here and scroll down to Link to Food Allergy Through the Skin?) in the evocatively named Journal of Investigative Dermatology that quoted another Brit, Dr. Carsten Flohr of King’s College, London: “This work takes what we thought we knew about eczema and food allergy and flips it on its head. We thought that food allergies are triggered from the inside out, but our work shows that in some children it could be from the outside in, via the skin. The skin barrier plays a crucial role in protecting us from allergens in our environment, and we can see here that when that barrier is compromised, especially in eczema, it seems to leave the skin’s immune cells exposed to these allergens.”
What a drag to think that a bowl of peanuts shared by an expectant mom and dad as they enjoy their remaining days as a couple in the run-up to delivery could result in sensitization in the months following the blessed event. I have been treating food-allergic patients for over thirty-five years. It used to be easier. We only had to answer one question: “to eat or not to eat?” Now it’s more like “to touch or not to touch?” and “To breathe or not to breathe?” Curiouser and curiouser.
I’m confused as to what this means for the skin prick test. If eczema leaves skin exposed to allergens, then does it not follow that a skin prick test for an allergen that has not been introduced into the diet can actually cause someone to be allergic to that very protein? I wonder this because my daughter, who has never consumed peanuts has been skin tested multiple times (she also has eczema), could this contribute to a future peanut allergy?
Thanks for your question. While I think this is a long shot, if nothing else it makes the case more strongly than ever that the most important factor in choosing to test for an allergen is a clinical history of symptoms. Testing should be used to help confirm a suspected allergy. It shouldn’t be a fishing expedition.
Dr. Paul Ehrlich