You’re standing in the drugstore aisle with a stick of deodorant, reading the back, and there it is: alpha-isomethyl ionone. A name that long deserves an explanation, and the label doesn’t give you one. Here’s what the graded evidence says, including the parts that are thinner than the scary ranking suggests.
Evidence key Strong Moderate Weak How we grade
The scent chemical in every tampon they tested
Start with the product you’d least expect to be scented.
The fragrance allergens found most in scented tampons were α-isomethyl ionone (in every tampon, 12.6-19.1 µg/g) and hexyl cinnamal, not the familiar citrus and lavender terpenes. Moderate evidence. Desmedt 2020
Sanitary pads, panty liners and tampons can contain undisclosed fragrance allergens, chiefly alpha-isomethyl ionone (in every scented tampon tested), hexyl cinnamal and benzyl salicylate, plus trace limonene, linalool and geraniol, and in the EU they do not have to declare any of them. Moderate evidence. Pastor-Nieto 2021 (Desmedt 2020)
And in your deodorant
The same chemical shows up under your arms.
Alpha-isomethyl ionone, an allergen on the EU's 1999 labeled list, was declared on 46.6% of 88 deodorants checked in 2007 and detected in about 65% of 23 analyzed deodorants (6-2,588 ppm); it was found in 21.7% of 516 consumer products in another survey. Weak evidence. SCCS 2012 (SCCS/1459/11)
It’s not only one chemical, either. A whole shelf of fragrance materials rides along.
Besides the fragrance-mix allergens, 14 other common fragrance materials (including linalool, benzyl acetate, and hedione) were found in 40-97% of the 73 deodorants tested in 1996; for three of them (hedione, linalyl acetate, alpha-isomethyl ionone) no published human contact-allergy case existed at the time despite their widespread use. Moderate evidence. Rastogi et al. 1998
What the EU says about it
In 2012 the EU's scientific committee on consumer safety (SCCS) classified 82 fragrance ingredients (54 chemicals and 28 natural extracts, including all 26 then labeled) as established causes of contact allergy in people, on clinical evidence alone. Strong evidence. SCCS 2012 (SCCS/1459/11)
Now the ranking for this particular chemical. We’d rather give you the weak grade than oversell it, so read the caveat before you quote the ranking.
Alpha-isomethyl ionone ranks as an established human contact allergen in the EU opinion (category ++, 11-100 reported cases), but individual patch-test studies found positive rates of 0% to 2.1%, and the industry's own review lists four negative human induction tests. Weak evidence. SCCS 2012 (SCCS/1459/11)
Hold the next rule apart from the tampon findings above. It covers cosmetics, and the tampon claim says those products don’t have to declare any of these.
The EU's fragrance-allergen labeling thresholds are unchanged by the 2023 amendment: an individual allergen must be named when it exceeds 0.001% in leave-on cosmetic products or 0.01% in rinse-off products. Strong evidence. Regulation (EU) 2023/1545
What 0.8 µg/cm² means
The EU committee put a number on a general exposure level, and then said what that number can’t do.
The EU committee said a general level of 0.8 micrograms per square centimeter (0.01%, 100 ppm in a product) would limit, but not prevent, allergic reactions in already-allergic people, and that ingredient labeling stays necessary. Moderate evidence. SCCS 2012 (SCCS/1459/11)
What we can’t tell you
We have no graded claim on how many people react to it today, how much a typical product contains, or whether a particular product will bother you. The tampon findings measure chemicals in products, not allergic reactions in users. We’d rather say so than guess. You shouldn’t have to guess either, and nobody should be able to keep this off the box.
What you can do
- Look it up on our alpha-isomethyl ionone page, or paste a whole label into the label decoder.
- A name on a label is the minimum. Ask for products with no added fragrance at all, and tell the brand you want it listed even when no rule makes them.
- Read more: fragrance allergy, deodorants and antiperspirants, women and fragrance, Europe vs. US fragrance rules, and the fragrance loophole.
Every claim above shows its evidence grade and names its source. See all the alpha-isomethyl ionone facts and the claims we won’t make. Information, not medical advice.
