You walk into your allergist’s office with a back covered in tape and pen marks. You walk out with a list of chemical allergens to avoid. For most people, it isn’t that straightforward. To the majority of people who are handed a list of chemicals to avoid, avoiding only the chemicals on that list isn’t enough. Each chemical can have several different chemical names, and might also go by any number of different trade or brand names as sold by various manufacturers.
Now add to that mix of chemical names the concept of cross-reactivity, or the tendency of the human body to sometimes react to chemicals that are similar in structure to the allergenic chemical. For example, a person who has an allergic reaction to propylene glycol could also react to polyethylene glycol, butylene glycol, or any number of other glycols. How do you wrap your mind around it all?
Brand names and trade names require research, but chemical names and families (related chemicals) are something you can learn. Consider the following:
The beginning parts of chemical names can be likened to adjectives, and the last half of the chemical names can be likened to nouns. Adjectives are words the help to further define or explain a noun, which is a person, place, thing, or idea. Soft kitten. The thing is a kitten, soft describes what the kitten is like. Brown dye. Dye is the thing, brown tells you what kind of dye. You can be allergic to kittens or dyes, but cannot be allergic to “soft” or “brown.” It wouldn’t make sense to avoid all brown things or all soft things. You might also only be allergic to brown dyes or soft kittens, and not all dyes or kittens.
Propylene glycol. The noun is glycol. That’s what chemical it is. The propylene designation tells us what kind of glycol by telling us about the “extras” that have been added to its structure. Methylisothiazolinone. The chemical is an isothiazolinone. “Methyl” tells us what kind of isothiazolinone by describing what modifications have been made to a basic isothiazolinone structure. Thus if you are allergic to propylene glycol you might be cautious of other glycols for cross-reactivity, but it would make no sense to avoid every chemical that is modified in a “propylene” manner. The same is true of isothiazolinones. You might be allergic to methylisothiazolinone, but that doesn’t mean you should avoid every chemical modified in a “methyl” manner, only that you might be wary of reaction to other isothiazolinones like methylchloroisothiazolinone.
Want a different analogy? Think of the chemical name as a person’s name. Bob Johnson. Now, you and Bob are in a pretty serious feud. Whenever Bob sees you, he throws a rock at you. Bob might keep the feud to himself and maintain hostilities only between the two of you, but he might tell his family, too – the whole Johnson clan. If he does tell his family, they might take your feud personally and start throwing rocks when they see you as well. It might be best to stay clear of Bob’s family (the Johnsons), but it wouldn’t be reasonable to think you should avoid every Bob in the world. There’s a pretty fair chance Bob Johnson knows nothing about most of those other Bobs and even if those other Bobs found out about your feud they wouldn’t take it personally. They’d see it as something between you and Bob Johnson.
Likewise, if decyl glucoside is your allergen, there’s no point in avoiding every chemical that begins with “decyl.” Those “decyl”-modified chemicals don’t share enough in common to care that you don’t get along with decyl glucoside. You might, however, want to be wary of other glucosides, like benzoyl-beta-D-glucoside and quercetin-3-0-glucoside. Those glucoside family members could harbour a grudge.
This is not a catch-all method of identifying cross-reacting allergens. Cross-reaction relies very much on molecular structure and receptors in your body, and not all chemicals are named in so straightforward a manner. This is, however, an excellent place to start.