Don’t take our word for it. Here’s every fact on this site, with its evidence grade, its caveats, and a link to the source, so you can check us.
We start you on the strong ones: findings that have been replicated or come from one large, well-controlled study. Moderate and weak facts are here too, labeled for what they are. Use “Link to this fact” to share a single card.
Skin allergy / Measured in people or real products
In people already allergic to cinnamal, a deodorant with just 0.01% of it triggered a reaction in 1 of 9, and 0.032% in 4 of 9; the industry limit is 0.05%, and it was set to prevent new allergies, not reactions in people already sensitized.
Strong evidence.
Caveats
Confirmed by the primary source, now in our evidence base: Bruze et al. 2003, an independent (non-industry, no COI declared), double-blind provocation study with a 20-patient non-allergic control group (0/20 reacted) and P<.001 statistics tying the reaction to both cinnamal-sensitization and the actively-scented axilla. The study's own authors recommend a deodorant limit below 0.01%, stricter than the 0.05% IFRA cap.
Source: RIFM Expert Panel 2005 (citing Bruze 2003), Food and Chemical Toxicology Industry-funded Link to this fact
Skin allergy / Measured in people or real products
In a double-blind study, deodorants containing as little as 0.01% cinnamic aldehyde (cinnamal) triggered allergic skin reactions within weeks in people already allergic to it, while an identical unscented deodorant on the other armpit, and the same deodorants used by 20 non-allergic people, caused no reactions.
Strong evidence.
Caveats
Small cohort (9 sensitized test patients, double-blind arm), but statistically significant (P<.001) with a concurrent negative control group and randomized/blinded contralateral-axilla design.
Source: Bruze et al. 2003, Journal of the American Academy of Dermatology Link to this fact
Skin allergy / Measured in people or real products
In a 5-year Danish patch-test survey of 17,716 eczema patients, 10.1% had fragrance allergy, and cosmetic products caused 42.1% of it; deodorants (25.3% of specific products listed) and scented lotions (24.4%) were the two leading culprits, together accounting for roughly half of all cases.
Strong evidence.
Caveats
Clinic-referred eczema patients (Danish Contact Dermatitis Group members' consecutive patients), not a general-population sample; retrospective database analysis, not a prospective cohort.
Source: Heisterberg 2011, Contact Dermatitis Link to this fact
Skin allergy / Measured in people or real products
Deodorants were significantly more likely to be the reported cause of fragrance allergy in men than women (37.9% vs 21.1% of listed products, odds ratio 2.3), while scented lotion (odds ratio 2.6) and fine fragrances (odds ratio 4.2) were significantly more often the reported cause in women; shampoo showed no sex difference.
Strong evidence: Reflects differential product use by sex, not necessarily differential susceptibility to sensitization.
Source: Heisterberg 2011, Contact Dermatitis Link to this fact
Skin allergy / Measured in people or real products
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.
Caveats
Small cohort (13 sensitized test patients fully tabulated of 35 enrolled), but statistically significant (P<.001) with a concurrent negative control group (0/10) and a randomized, double-blind, contralateral-axilla design; unblinding confirmed the active deodorant caused every reaction.
Source: Bruze et al. 2005, Contact Dermatitis Link to this fact
Information, not medical advice. See also: myths we won’t tell you.