# B12 alergies and avoidance: How?

**URL:** <https://boards.straightdope.com/t/b12-alergies-and-avoidance-how/603108>\
**Category:** Factual Questions\
**Created:** [November 16, 2011, 12:13pm UTC](https://boards.straightdope.com/t/b12-alergies-and-avoidance-how/603108 "2011-11-16T12:13:03Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\
**Post date:** [November 16, 2011, 12:13pm UTC](https://boards.straightdope.com/t/b12-alergies-and-avoidance-how/603108/1 "2011-11-16T12:13:03Z")

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I was doing some reading about B12 on Wikipedia, and I noticed that it was mentioned that there was a rare allergy. I’ve looked this up on Google, and everything mentions that someone with an allergy should avoid B12.

But how is that possible? B12 is a necessary vitamin, and its deficiency syndrome is rather bad. How do people with the allergy get the vital nutrient?

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**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\
**Post date:** [November 16, 2011, 1:46pm UTC](https://boards.straightdope.com/t/b12-alergies-and-avoidance-how/603108/2 "2011-11-16T13:46:40Z")

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At least some of the reported cases have been in people getting regular injections of B12 for pernicious anemia (caused by B12 deficiency), and it’s thought that a preservative or other component of the shots is spurring the allergic reactions.

Not sure if this link will work for you, but [desensitization](http://onlinelibrary.wiley.com/doi/10.1111/j.1398-9995.2007.01389.x/full) is said to have been effective in allergic patients.

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<div class="post-metadata">

**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\
**Post date:** [November 17, 2011, 10:17am UTC](https://boards.straightdope.com/t/b12-alergies-and-avoidance-how/603108/3 "2011-11-17T10:17:34Z")

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> [@Jackmannii](#):
>
> At least some of the reported cases have been in people getting regular injections of B12 for pernicious anemia (caused by B12 deficiency), and it’s thought that a preservative or other component of the shots is spurring the allergic reactions.
> 
> Not sure if this link will work for you, but [desensitization](http://onlinelibrary.wiley.com/doi/10.1111/j.1398-9995.2007.01389.x/full) is said to have been effective in allergic patients.

I indeed could read it, and it is quite informative. Particularly the part about desensitization being temporary. Thank you.