You get a rash after a scented product, and the question comes right away: is this an allergy? It might be. It might also be irritation, which needs no allergy at all. Telling the two apart is harder than it should be, and the studies below show why.
Evidence key Strong Moderate Weak How we grade
One armpit scented, one not: only the allergic reacted
The cleanest evidence comes from deodorant trials, where one armpit got the scented product and the other got an identical unscented one.
In a controlled study, deodorants containing hydroxycitronellal at 0.032% to 0.32% triggered allergic armpit rashes within a few weeks in all 7 people already allergic to the chemical, while an identical unscented deodorant on the other armpit, and the same deodorants used by 7 non-allergic people, caused no reactions (P<0.001). Moderate evidence. Svedman et al. 2003
In a double-blind study, deodorants containing isoeugenol at concentrations from 0.0063% to 0.2% triggered allergic skin reactions within weeks in 10 of 13 people already allergic to it, while identical unscented deodorants and the same products used by 10 non-allergic people caused no reactions. Strong evidence. Bruze et al. 2005
The people who reacted were already allergic. The people who weren’t had no reaction. The full story on this kind, including why the standard test misses so much, is in our fragrance allergy guide.
Fragrance sits on both lists
One narrative review puts fragrance on both sides of the line.
Fragrance causes both irritant and allergic contact dermatitis, among other adverse skin reactions, and fragrances are the most frequent chemicals causing contact dermatitis overall. Weak evidence. Pastor-Nieto 2021
Contact allergy is common, and fragrance allergy is real.
About 1 in 5 people in the general population (20.1% of 20,107 people patch tested in 28 studies) are allergic to at least one common chemical that touches the skin, such as nickel, fragrance, preservatives, or hair dye. Strong evidence. Alinaghi 2018
Fragrance ingredients rank alongside nickel as a leading cause of contact allergy in dermatology-clinic eczema patients, diagnosed in roughly 10-12% of those tested. Strong evidence. Johansen 2003, Am J Clin Dermatol 4(11):789-798
Some rashes need no allergy at all
Now the other kind. The cosmetics industry’s own safety panel found a reaction in most people tested, and still called the ingredients safe.
The cosmetics industry's own safety panel found that 5% benzyl alcohol and 2% benzoic acid provoke a non-allergic skin reaction (redness, swelling, itching) in most people tested with no prior sensitization needed, yet concluded both are "safe" up to 5% in cosmetics because it judged typical exposure limited, not because the reaction is rare. Moderate evidence. Nair 2001 (CIR Expert Panel) Industry-funded
Disinfectants and antiseptics are in the same boat.
Antiseptics and disinfectants are known skin irritants, especially when strong, used for long periods, under occlusion, or on damaged skin, and many can also cause true contact allergy that reviewers think is under-diagnosed. Moderate evidence. Lauriola 2025
One weak laboratory study tested neat limonene and linalool after prolonged air exposure. It did not test product storage, so don’t treat it as a rule.
Keep scented products closed and avoid old, long-opened ones: limonene and linalool became skin irritants after weeks of air exposure. Weak evidence. Bråred Christensson 2009 Industry-funded
One positive test, two possible meanings
A patch test is supposed to settle the question. In the studies below, a positive result did not always separate allergy from irritation.
Benzalkonium chloride, a cationic disinfectant and antiseptic ingredient, can cause both irritant and allergic contact dermatitis; the standard patch-test preparation is only 0.1% in water because higher concentrations irritate, and some authors think sensitization is likelier from disinfectant-strength use (above 1%) than from preservative use (0.01% or less). Moderate evidence. Lauriola 2025
In a Boston patch-test clinic, 32% of 615 dermatitis patients reacted to benzalkonium chloride (BAK), a preservative and disinfectant, and about 1 in 10 (10%) reacted strongly; the authors say weak reactions may be irritation rather than allergy. Moderate evidence. Isaac 2017
Another clinic reported it differently.
At the Mayo Clinic, 8.8% of 8,448 patients patch tested to benzalkonium chloride (BAK), a disinfectant and preservative, in 2000-2012 had a positive reaction, up from 5.5% in 1998-2000, and only 1.3% were called irritant. Moderate evidence. Wentworth 2016
Laundry detergent shows the same difficulty.
At the 0.1% aqueous test concentration used for detergents, irritant or questionable reactions (11-12 patients, 1.5-1.6%) outnumbered clearly allergic-looking reactions (5 patients, 0.7%), showing these test concentrations already sit close to the irritant threshold, which limits how much higher a concentration could be used without generating false positives. Moderate evidence. Belsito et al. 2002 Industry-funded
Of the only 2 patients whose detergent patch-test reaction could be further evaluated with dose-response testing and a blinded T-shirt wear test, one had a negative repeat test and use-test suggesting the original reaction was likely irritant, not allergic, and the other reacted equally to a fabric swatch laundered without any detergent as to one laundered with detergent. Moderate evidence. Belsito et al. 2002 Industry-funded
Even a deodorant solvent can play both parts.
Propylene glycol, a solvent and humectant used in many deodorants, can make up as much as 73% of the product and acts as both a skin irritant and an allergen, which makes its allergy patch tests hard to interpret (positivity ranges 0.1%-3.8% across studies). Moderate evidence. Musicante 2024 Industry-funded
It cuts both ways
None of this means allergy is the smaller problem.
In an Italian series of 277 people with confirmed clothing (textile) dermatitis, 58.3% had a true skin allergy and the rest an irritant reaction; about 8 in 10 of the allergic were allergic to textile dyes, and Disperse Blue 124 alone was positive in 54.5%. Moderate evidence. Lisi 2014
And a positive test isn’t always the answer either.
The Society also names 'Nonallergens of the Year': thimerosal (2002), because only 16.8% of its frequent positive patch tests (10.9% of 4,087 patients in 1996-1998) were relevant, and parabens (2019), which it calls one of the least allergenic preservatives. Moderate evidence. Militello 2020
The label won’t sort it out for you
If you hoped a word on the front of the package would do the sorting, look at the rules behind that word.
The US FDA has no directive at all regulating the use of the word 'hypoallergenic' on a cosmetic product, and in a 2015 survey the products so labeled had the highest contact-allergen rate (88.2%) of any of four marketing terms tested (hypoallergenic, dermatologist recommended, fragrance free, paraben free). Strong evidence. Hamann 2015
If you have fragrance allergy or eczema, don't rely on "fragrance free", "hypoallergenic" or "dermatologist recommended": in best-selling US moisturizers these claims often coexisted with listed skin allergens, so check the full ingredient list or a dermatologist-checked product list. Moderate evidence. Xu 2017
What testing can and can’t tell you
People with a dermatitis distributed under clothing who suspect laundry detergent can ask a dermatologist for patch testing with a 0.1% aqueous dilution of their own detergent (low enough to avoid most irritant false positives), but a single positive reaction needs further dose-response and use-testing to separate true allergy from irritation. Moderate evidence. Belsito et al. 2002 Industry-funded
Product-specific testing can find what the standard panel misses.
In a 4-year German patch-test study of 1,468 patients tested with their own deodorants and perfumes, 129 had positive reactions to a specific product, and 58 of them (45%) were missed by the standard fragrance-mix, balsam-of-Peru, and lyral patch tests. Moderate evidence. Martini 2020
What you can do
- Check what’s actually in the product with our label decoder, and read why “unscented” isn’t the same as fragrance-free.
- Whatever the mechanism, you can ask for fragrance-free spaces where you live and work. Print a sign, write a letter, or start with ask for fragrance-free.
- Get the overview in Allergy or irritation?, then read why the studies keep pointing to irritation.
Every claim above shows its evidence grade and names its source. See all the facts and the claims we won’t make. Information, not medical advice.
