Tokyo Food Safety Information Center » Tokyo Metropolitan Government food safety FAQ » I hear that an immediate allergic response can occur due to mites propagating in flour-milled products after opening. Is it true?

I hear that an immediate allergic response can occur due to mites propagating in flour-milled products after opening. Is it true?

I hear that an immediate allergic response can occur due to mites propagating in flour-milled products after opening. Is it true?

  • Immediate type allergy cases (anaphylaxes) due to ingestion of mites in flour-milled products have been reported both within Japan and overseas.

  • Consume flour-milled products, such as okonomiyaki and pancake mixes, as soon as possible after opening. If some part is not consumed and left over, it is effective to store it in a refrigerator.


More information


Okonomiyaki mix

<Past allergic cases: >

  • Reported cases indicate the allergic reactions were caused by consumption of dishes prepared by heating flour-milled products such as okonomiyaki and pancake mixes that contained mites.
  • In many cases, the flour-milled products had been kept at room temperature for several months to several years after opening.
  • Major symptoms include: cutis symptoms (erythema (red spots), nettle rash, and itching on whole body) and breathing difficulty but in some cases, whole-body anaphylaxes, such as lowering of consciousness and shocks, may occur.  In most cases, the symptoms appear immediately after ingestion or within one hour.

<Why do mites enter flour-milled products?>

  • For mites, products such as okonomiyaki and pancake mixes, which contain starch, protein, umami components, etc., are extremely convenient food sources.
  • As mites are very small with a body length of 0.3-0.5 mm, they can enter the bag after opening only if it has even an extremely small clearance.  It is reported that in flour-milled products stored in households, mites have been detected from products kept in bags with the openings folded and closed with rubber bands or clips, and even from those kept in airtight containers.

<What should we pay attention to?>

  • The mite allergen is strong against heat and thus heating in cooking cannot prevent the allergic symptoms to occur.
  • When consuming flour-milled products such as okonomiyaki and pancake mixes, use them up as quickly as possible after opening.
  • If some portion is not consumed and left over, store it in a refrigerator to prevent proliferation of mites.  Even if it is stored in a refrigerator, use it up as quickly as possible.

Bureau of Public Health, Tokyo Metropolitan Government
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