Balsam of Peru

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 for this site, not a substance at all.

A mixture, not a chemical

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

The reason is that it is a natural resin containing dozens of constituents, several of which are sensitising, and no one of them is present in enough quantity to test alone. Testing the mixture is the only way to catch the reaction.

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

So a positive test tells you that you react, and does not tell you to what. That is a genuinely unsatisfying result and it is the honest one, which is why it is worth knowing before rather than after.

Where it appears

In cosmetics and toiletries, as a fragrance and fixative, under its INCI name Myroxylon Pereirae Resin or as balsam of Peru.

In flavourings and food, which is what makes it different from most fragrance allergens. It is related to the flavour compounds in cinnamon, cloves, vanilla and citrus peel, and it turns up in flavoured drinks, baked goods, confectionery and spiced products.

That dual life is why this page sits in two clusters. Someone with a confirmed balsam of Peru allergy may be given dietary advice as well as a list of products to avoid, and that is a clinical decision rather than a label-reading one.

The names that will not help you

Here is the part a scanner cannot fix. On a cosmetic label the resin is named, so it can be found. In food it is essentially never named as balsam of Peru, because it is not the ingredient; the related flavour compounds are, and they arrive inside flavouring, natural flavouring or a spice.

So the same substance is findable in one aisle and invisible in the other, and the invisible aisle is the one where a diet has to be managed.

Its relatives

Eugenol is the clearest overlap: it is the main compound in clove, it is tested separately in the same series, and someone reacting to one may react to the other.

Cinnamal, cinnamyl alcohol and Limonene sit in the same territory of substances that are simultaneously fragrance materials and flavour compounds. The general shape of the problem, including the fact that fragrance may be declared as one word, is on the fragrance allergy page.