Are people allergic to Roundup?

Expert response from Dan Goldstein

Former Senior Science Fellow and Lead, Medical Sciences and Outreach, Monsanto Company

Friday, 11/03/2016 11:54

To provide a short answer:

There is no evidence of allergic reactions to glyphosate or other components of glyphosate-based formulations from oral exposure (e.g. glyphosate residues on food).  You might have been asking this question because you were interested in food allergies, but since that was not specified I’m going to give a more comprehensive answer. 

We do see allergic skin reactions (e.g. contact dermatitis, a poison-ivy-like reaction) following the use of some glyphosate-based products.  Based on analysis of case reports this is most commonly from plants or other exposures, but a few cases are product-related and are most likely due to antimicrobial agents in “ready-to-use” products.  Concentrate products generally do not contain antimicrobial agents.

There are many brands of glyphosate-based formulations, glyphosate being the active ingredient in Roundup® branded herbicides and similar formulations.  The other ingredients are surfactant (soapy substance like detergent), water, and minor ingredients at small concentrations which may include colorants, anti-foaming agents, and anti-microbial agents (e.g. biocides).

There is no evidence that humans or animals develop allergy to glyphosate.  Glyphosate is a small molecule and, in and of itself, cannot induce allergic sensitization.  Small molecules that induce allergic reactions (like penicillin) do so by reacting with and binding to proteins in the blood or on cells (a process called hapten formation) to create a “target” big enough to trigger an immune response.  These reactions do not occur with glyphosate, which is excreted unchanged from the body in urine.  We are required to do animal skin sensitization testing of pesticides and formulations.  While the results may not be 100% predictive of human skin responses, we can say that glyphosate is not a skin sensitizer in animals (guinea pigs).

There have been reports of skin reactions from glyphosate-based formulations but the cause is difficult to determine because reports involve exposure to plants -the number one cause of allergic dermatitis. There are a few reports of skin reactions when exposure to plants or other sensitizers is unlikely; and in a few cases doctors have challenge-tested patients and demonstrated sensitization to glyphosate products.  The ingredients in glyphosate formulations are generally not known allergic skin sensitizers.  However, ready-to-use formulations require anti-microbials to prevent the growth of microorganisms which degrade the product, clog sprayers, or present an infection hazard.  Anti-microbials are chemically reactive- it’s how they kill the “bugs”- and the commonly used anti-microbials  are known allergic sensitizers in animals and humans. 

Consumers prefer ready-to-use products for many reasons related to cost, convenience, and safety.  While these products must contain anti-microbials, they avoid risk of eye or skin exposure to concentrated products and avoid exposure related to measuring and mixing of concentrate products.  The anti-microbials used in glyphosate products are used in a variety of consumer products such as liquid soaps and cosmetics, and are approved for these uses as well as for use in pesticide products.  The most commonly used anti-microbial in ready-to-use products in the US is a photo-sensitizer biocide (benzisothianzolin-3-one), meaning that exposure to the chemical on skin, followed by sunlight exposure (which results in chemical reactivity) can cause an allergic response. You might be wondering:  What about allergy labeling for glyphosate products?  

With over 6 billion people on the planet, all with their own propensity to react to different things, it is essentially impossible to establish that any chemical will never cause an allergic response under any circumstances. Even with human testing (as used for cosmetics), if you test 100 people and see no response statistically you can only be sure that less than 3% of the population will respond.  Because allergy potential depends on concentration and other factors, and because many foods and chemicals occasionally cause allergic skin reactions, labeling of products for allergic skin reactions is generally NOT based on whether a reaction has ever been reported or whether the product contains an ingredient which can cause allergies (although there are a few examples where frequent reports of human skin reactions have been a reason for labeling).  Rather, we test actual pesticide formulations. A positive result in these tests is what triggers labeling such as “may cause allergic skin reaction”.

Very few glyphosate products are labeled as sensitizers.  This does not mean sensitization is completely impossible, only that it is not a likely or frequent occurrence. The causes of individual reactions can be hard to sort out, but we are aware of some cases of potential allergic skin reactions to glyphosate-based products, mainly in the case of ready-to-use formulas which may contain anti-microbial agents known to cause skin allergies.