Egg on one's face

September 3, 2016 8:45 AM

Twice I have had an allergic reaction to egg white on my facial skin (note: the reasons for egg being on my face are irrelevant). This manifested in the classic response of a contact allergy: major swelling, redness, and itching. Since then I have had my blood tested for allergy to egg white and yolk (separately), but both showed no allergy response. Why not?

In my (limited) understanding of blood tests for allergies, shouldn't an allergic skin response also be detectable in the blood? Or do I specifically need a skin prick test (on my face)?

posted by Socky McSockface to Health & Fitness (6 answers total)

I don't know about food allergies, but I do know that I have had disagreeing results between skin prick and blood tests (neither of which seem to line up precisely with the actual reactions I have, either). My skin prick for dust mite invaded all the nearby tests and itched for a long time; the blood test I had a year later claimed I had no dust allergy at all. (I very clearly and strongly react to actual dust in my life). I don't know why the blood test didn't show a reaction- maybe it was done wrong, maybe they tested a different protein (it was on a new continent), maybe there's some reason my skin/eyes/mucous membranes react but my blood doesn't. But that was the combo of test results I ended up with.
posted by nat at 9:34 AM on September 3, 2016 [1 favorite]

My allergist told me there is a high false negative rate on the blood test (maybe 10%?). This after I tested negative on nuts despite having an actual allergy (skin tests positive years ago, and reactions any time I accidentally ate or touched nuts). The gold standard for food allergies is the food challenge, and it seems like you had an actual reaction, so you are most likely allergic. Allergies are weird. Testing is not perfect.
posted by Valancy Rachel at 9:42 AM on September 3, 2016 [3 favorites]

Food (in specific) allergy tests are pretty flaky in my opinion. I'm completely unallergic to peanuts, meanwhile various types of fish put me into anaphylactic shock -- testing has revealed that actually, contrary to reality, I'm deathly allergic to peanuts and not any type of fish. Ooooook.

> Allergies are weird. Testing is not perfect.

Yep!
posted by so fucking future at 10:01 AM on September 3, 2016

Echoing the above, my kids' allergist was careful to explain that there is apparently a difference between food allergies and eczema triggered by certain foods and since I was trying to comfort two screaming, rashy infants I basically said well, since they both break out in weeping hives when they ingest dairy, I'm going to call it an allergy and leave it at that.

Testing on both kids shows that one should only be mildly allergic and the other is very allergic but either way, they don't get dairy.
posted by annathea at 10:12 AM on September 3, 2016

Blood tests for allergies generally look for antibodies, and perhaps your reaction to egg whites is a purely cell-mediated immune response:

Cell-mediated immunity is an immune response that does not involve antibodies, but rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.

As I understand it, though this is not mentioned in the linked article, such T-cell mediated reactions are often delayed a day or so if you haven't been exposed to the offending substance for quite a while.
posted by jamjam at 11:02 AM on September 3, 2016 [1 favorite]

I have had allergies since forever, and been tested many times. Often results vary (although I have found that over time, at least in my case, usually the biggest offenders show themselves). Anyway, although perhaps jamjam is correct, or the test was whatever - is it at all possible that something else mixed in with the egg caused it? (Unless it was of course, just egg. :)
posted by bitterkitten at 1:15 PM on September 6, 2016