Allergies to germs
March 11, 2025 5:22 PM Subscribe
"Mum, are there some people allergic to germs?"
My 4 year old asked me this yesterday and I thought I'd bring it to you lovely folk at Metafilter.
She knows that germs are very small and can make you sick. She knows that her cousin is allergic to eggs, and that we can't take peanuts to kinder. She has a basic understanding of how allergies work because I have some allergies as well.
My hunch is that since viruses contain proteins, it's possible?
My 4 year old asked me this yesterday and I thought I'd bring it to you lovely folk at Metafilter.
She knows that germs are very small and can make you sick. She knows that her cousin is allergic to eggs, and that we can't take peanuts to kinder. She has a basic understanding of how allergies work because I have some allergies as well.
My hunch is that since viruses contain proteins, it's possible?
If bacteria count as germs, then "certain bacterial species promote the development and exacerbation of allergic inflammation". (According to this paper whose quality I do not have the background to evaluate.)
posted by trig at 6:04 PM on March 11
posted by trig at 6:04 PM on March 11
As someone who has occasionally gotten hives at the end of a cold virus, and once gone into anaphylactic shock from it, yes. Not sure if it’s technically an allergy, but my immune system does react to certain viruses like it does to food I’m allergic to.
posted by Valancy Rachel at 7:56 PM on March 11 [3 favorites]
posted by Valancy Rachel at 7:56 PM on March 11 [3 favorites]
What we usually call allergy are type I hypersensitivity reactions (there are other types, for example contact dermatitis is caused by a type IV hypersensitivity reaction which is a distinct mechanism). Type I hypersensitivity reactions involve the release of histamine through mast cell degranulation caused by allergens (proteins) cross-linking IgE bound to the surface of the mast cell. Mast cells' main job in your immune system is to fight parasites, which cross-link the IgE bound to the surface in the same way.
Parasite infections can cause the same kinds of symptoms as allergy (rash if they get into your skin or mucus membranes, coughing if in your lungs and even anaphylaxis in some cases) because they are activating the same mechanism. So in some sense, your immune system's reaction to a parasitic infection can be similar to an allergy.
But if by germs you mean viruses and bacteria specifically, then it seems theoretically possible that a protein from a virus or bacteria could cause cross-linking of IgE on mast cells. In order to get an allergy reaction, you first need sensitization through exposure to the antigen that causes B cells to mature into plasma cells that produce IgE. But when you have a viral or bacterial infection, your immune system focuses on producing some of the other four types of immunoglobulins (IgG, IgM, etc), so it probably wouldn't produce significant quantities of IgE to germ antigens (B cells switch through the different types of immunoglobulins in a specific order and IgE is the last one). Perhaps if something went wrong, due to immune deficiency of some type or some kind of chronic infection, there would be sufficient IgE production to germ antigen to sensitize your immune system by arming mast cells. But that's already stretching my knowledge of immunology!
Immunology is complicated and we don't have a great understanding of how everything works (including allergy). We've really only been starting to put the pieces together over the last hundred years and getting into the details of mechanisms over the last fifty. So I wouldn't be surprised if the answer is that we simply don't know.
posted by ssg at 8:38 PM on March 11 [9 favorites]
Parasite infections can cause the same kinds of symptoms as allergy (rash if they get into your skin or mucus membranes, coughing if in your lungs and even anaphylaxis in some cases) because they are activating the same mechanism. So in some sense, your immune system's reaction to a parasitic infection can be similar to an allergy.
But if by germs you mean viruses and bacteria specifically, then it seems theoretically possible that a protein from a virus or bacteria could cause cross-linking of IgE on mast cells. In order to get an allergy reaction, you first need sensitization through exposure to the antigen that causes B cells to mature into plasma cells that produce IgE. But when you have a viral or bacterial infection, your immune system focuses on producing some of the other four types of immunoglobulins (IgG, IgM, etc), so it probably wouldn't produce significant quantities of IgE to germ antigens (B cells switch through the different types of immunoglobulins in a specific order and IgE is the last one). Perhaps if something went wrong, due to immune deficiency of some type or some kind of chronic infection, there would be sufficient IgE production to germ antigen to sensitize your immune system by arming mast cells. But that's already stretching my knowledge of immunology!
Immunology is complicated and we don't have a great understanding of how everything works (including allergy). We've really only been starting to put the pieces together over the last hundred years and getting into the details of mechanisms over the last fifty. So I wouldn't be surprised if the answer is that we simply don't know.
posted by ssg at 8:38 PM on March 11 [9 favorites]
Also, there are allergic reactions that aren't directly allergic reactions to germs, but involve them. For example, EBV and CMV (both viruses in the herpes family) can cause someone who is infected to become allergic to certain antibiotics.
posted by ssg at 8:49 PM on March 11
posted by ssg at 8:49 PM on March 11
The cell walls of a major group of bacteria, the Gram-negatives, are made of lipopolysaccharide, which triggers an inflammatory response. This is not what an immunologist would call an allergy; it's not through the adaptive immune system learning an unwanted response.
This is through the innate immune system, by a receptor specifically tuned for this bacterial signal -- it just plays out unfortunately for you if there's too much LPS dumped by lysing bacteria. So not quite on target for what you're looking for. But it's a medically significant immune response with the fun fact that nickel 'allergy' is by the same receptor.
posted by away for regrooving at 9:15 PM on March 11 [1 favorite]
This is through the innate immune system, by a receptor specifically tuned for this bacterial signal -- it just plays out unfortunately for you if there's too much LPS dumped by lysing bacteria. So not quite on target for what you're looking for. But it's a medically significant immune response with the fun fact that nickel 'allergy' is by the same receptor.
posted by away for regrooving at 9:15 PM on March 11 [1 favorite]
Oh if you include autoimmune responses, there's lots unfortunately. These are the adaptive immune system's learned response to the pathogen becoming a problem for the host. But not an allergy histamine sneezing / hives / anaphylaxis problem, rather the antibodies match a self-antigen and the actual immune self-attack is the problem.
Group A strep is a common trigger, causing "rheumatic fever" symptoms.
posted by away for regrooving at 9:28 PM on March 11 [2 favorites]
Group A strep is a common trigger, causing "rheumatic fever" symptoms.
posted by away for regrooving at 9:28 PM on March 11 [2 favorites]
In a certain way, illness caused by germs *can* be compared to allergy, as our biosphere is incompatible with theirs. So their invasion causes our body to react with an immune response, rather than synergistic or at least, non-interfering co-existence, much like gut bacteria.
posted by kschang at 11:42 PM on March 11
posted by kschang at 11:42 PM on March 11
In order for an immune response to count as an allergy, it must be mediated by igE, one of the five immunoglobulin isotypes.
And yes there are people who have igE reactions and allergies to pathogenic bacteria. Specifically, some people with Atopic Dermatitis have igE antibodies and allergies to S. aureus bacteria:
And yes there are people who have igE reactions and allergies to pathogenic bacteria. Specifically, some people with Atopic Dermatitis have igE antibodies and allergies to S. aureus bacteria:
Conclusion and Clinical Relevanceposted by jamjam at 12:41 AM on March 12 [4 favorites]
Specific IgE reactivities against a variety of bacterial antigens were observed in a subgroup comprising a third of AD patients and may contribute to allergic inflammation.
You need to speak 4 year old here. In that language, "Allergic to" means "gets sick from things that don't seem visibly dangerous." So no long complex explanation about biological processes really matters here. It's a preschool level analogy and it's true for the task of figuring out that bodies react badly to some invisible elements of things.
posted by ponie at 9:52 PM on March 12
posted by ponie at 9:52 PM on March 12
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posted by pullayup at 5:59 PM on March 11 [3 favorites]