What is a balsam of Peru allergy?

Balsam of Peru is a resin from a tree that does not grow in Peru, and it is one of the most significant contact allergens there is. It is also, unusually, not a substance.

Why it is tested at 25 percent

Most entries in a patch test series are single compounds at one percent or less. Balsam of Peru is tested at 25 percent, by a distance the highest concentration in the European baseline series.

That is not because it is twenty-five times more dangerous. It is because it is a natural mixture of dozens of constituents, several of them sensitising, and no single one is present in enough quantity to test on its own. Testing the whole resin is the only way to catch the reaction at all.

Which is why the result is frustrating

The guideline states the consequence directly: where a positive reaction concerns a natural mixture, “it may not always be possible to pinpoint a particular sensitizer”.

So the test can tell you that you react, and cannot always tell you to what. That is an honest limit rather than a failure of the test, and knowing it in advance is better than discovering it afterwards.

It lives in two aisles

This is what separates it from most fragrance allergens.

In cosmetics it is named, as balsam of Peru or under its INCI name Myroxylon Pereirae Resin, so it can be found on a label.

In food it essentially never is. It is related to the flavour compounds in cinnamon, cloves, vanilla and citrus peel, and those arrive inside flavouring, natural flavouring or a spice.

The same substance is findable in one aisle and invisible in the other, and the invisible one is where a diet has to be managed. That is why dietary advice sometimes comes with this diagnosis, and it is a conversation with a dermatologist and a dietitian rather than something a label can settle.

Its overlaps

Eugenol is the clearest: the main compound in clove, tested separately at 1 percent within fragrance mix I, and someone reacting to one may react to the other.

Cinnamal, cinnamyl alcohol and the citrus terpenes sit in the same territory of substances that are fragrance and flavour at the same time. The general picture, including why the word fragrance can stand for dozens of substances at once, is on the fragrance allergy page.