What is the meaning of the SNOMED concept Allergen which categorizes 6105 substances? Face value would come up with …

if a substance CAN BE the cause of an Allergy then it is an Allergen

In other words, Allergen is a grouping concept for substances that can cause allergies. Or is it?

SNOMED disorder axis has 1597 allergies to substances but only 1133 of those substances are classed as Allergens. In other words, SNOMED comes with allergies to substances that it doesn’t consider to be Allergens. Examples include Allergy to Oats whose cause, Oats, isn’t classed as an Allergen.

And the choice of what is and what isn’t an Allergen seems arbitrary. Of 54 fresh fruits, only 9 are said to be allergens. Strawberries are in, Raspberries out. Try a little meat. Pork is in, but its peer, Lamb is out.

And there’s more. Allergen itself breaks into Drug Allergen and Food Allergen. Surely a Food Allergen is a Food and a Drug Allergen, a Drug. But here are 25 foods that make it into Drug Allergen, including that well know drug, the Cherry.

All in all, in this condition, neither Allergen nor its specializations are good for anything.

Update: So I posted a variation of the above to the Substance Hierarchy Reworking group of SNOMED’s master, the IHTSDO and here’s what Matthew Cordell wrote …

Realistically it’s impractical/impossible to define the range of substance that “could” cause an allergy in “somebody”. Consequently such relationships aren’t really “defining” … defining something as being an “allergen” is actually saying a “a potential allergen” – which is circumstantial. … the allergen categories will most likely be retired

Circumstantial, not Defining, that says it all. Now, our SNOMED dataset has to reflect this. In general, it needs to do a better job at hiding or downgrading clutter.