So who's right?
The skin is a surprisingly complex and tricky organ. I don't pretend that this blog post will lay it all out neatly for you. There are a lot of avenues to explore, including the distinction between skin manifestations of ingested gluten versus actual skin reactions to surface contact with gluten. But by taking a peek into the peer-reviewed scientific literature, you can open a valuable window into answering the question: Can you react to gluten just through surface contact on your skin?
Spoiler alert: the short answer is yes (for some of you).
But first, we need to get a wee bit of background info and definitions out of the way, so that the discussion of the various studies makes sense.
Your body has at least five major antibody responses. Two are important here:
- IGG/IGA - these two are associated with celiac disease, and potentially with non-celiac gluten sensitivity
- IGE - a true allergy, known as Type I, which has the potential for anaphylactic response
- Atopic dermatitis - can involve scaly, itchy rashes; blisters; dry skin
- Urticaria - hives, itchy red welts
- Contact dermatitis - a cell-mediated Type IV response to surface exposure to an irritant (such as poison ivy)
- Oral challenge - ingested gluten that may cause a skin response
- Skin prick test, intradermal injections - introduce gluten into the layers of the skin to monitor for response
- Patch test - surface application of gluten to monitor for contact response over period of time
Okay, with that super basic overview out of the way, let's dive into the details, starting with a subject closest to the MO legislator's proposal: cosmetics.
Reactions to gluten in cosmetics
A number of studies and case studies—including from 2000, 2006, 2007, and 2012—all found identical results: contact urticaria (hives) in response to surface skin contact with a variety of cosmetics products, including lotions. The common culprit was hydrolyzed wheat protein (HWP), even in subjects who otherwise tested negative for skin reactions to regular wheat and gluten. HWP, researchers concluded, was particularly allergenic.
Skin reactions to gluten among bakers and other food preparers
Bakers and other food preparers who come into regular contact with wheat flour have been known to develop protein contact dermatitis, as evidenced—for example—by one study from 1993 and another from 2006, in which one third of study subjects developed atopic contact dermatitis.
Skin reactions among celiac disease patients
Early studies from 1976, 1977, and 1980 all found that intradermal (within the skin) injections of gluten caused skin reactions, including among as many as one third of celiac patients in one study. However, I failed to find studies that more explicitly associated surface contact with wheat/gluten with skin reactions among celiac disease patients.
This extensively studied condition is sometimes called the skin manifestation of celiac disease. Researchers from a 2006 study failed to produce skin reactions to intradermal injections of gluten fractions. This suggests that DH's skin rashes are associated with ingested gluten, though many other variables may come into play, and the study group was small.
Ingested gluten manifesting in the skin
But to the point of ingested gluten manifesting as skin reactions, a number of studies, including one from 2000, found that ingested gluten initiated an IGE antibody allergic response that manifested as atopic dermatitis. In such cases, a gluten-free diet reciprocally resolved the dermatitis. Thus what may appear to be a surface skin reaction to gluten is actually caused (and resolved) by the presence (or absence) of ingested gluten in the diet.
Skin reactions in wheat allergy
Compared to the IGG/IGA response of conditions such as celiac disease, the IGE pathway of wheat allergy offers additional insight. In a 1999 study of children with confirmed wheat allergy, 86% had a positive patch test. In other words, their skin reacted to surface contact with gluten. Two years later, a 2001 study, again of children with confirmed wheat allergy and atopic dermatitis, found that an atopy patch test (surface skin exposure to wheat) had a 94% positive predictive value. More recently, a 2008 study again confirmed the surface contact skin reaction to gluten among those with wheat-allergic atopic dermatitis.
Finally, in a 2004 study that bridged the worlds of celiac disease and wheat allergy, researchers found that a small percentage of patients with celiac disease also had wheat allergy, including a higher rate of IGE-associated atopic dermatitis. For such patients, they may have skin reactions to surface contact with gluten, but it's not their celiac disease at work, it's the wheat allergy.
As you can see, trying to answer the question of whether you can develop a skin reaction to surface contact with gluten turns up a complex network of conditions, tests, and results. But at the end of the day, some take-home lessons become clear. Whether due to celiac disease, dermatitis herpetiformis, wheat allergy, or another condition, you may develop skin manifestations of ingested gluten, but you may also have the potential for contact-related reactions to wheat/gluten. This latter population appears to be a minority, but their experiences of sometimes severe reactions to skin contact with gluten—such as via the hydrolyzed wheat protein of a shampoo—are very real.
Will you react to skin contact with gluten? I can't say. But it's clearly within the realm of possibility. For some the touch, the feel, of gluten is decidedly unpleasant, to say the least.