Every fact on this site, with its evidence grade, its caveats and a link to the source.
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.
What you can do / Measured in people or real products
If you have unexplained or recurring dermatitis, ask whether patch testing will include oxidized linalool (and oxidized limonene); standard fragrance tests missed 60% of these allergies.
Strong evidence: Hydroperoxide tests now recommended for baseline series in Europe.
Source: Christensson 2012, Contact Dermatitis Link to this fact
What you can do / Review of other studies
People with suspected fragrance dermatitis should ask for patch testing that includes oxidized limonene and linalool, because standard fragrance screens miss many cases.
Moderate evidence.
Source: Sukakul 2024, Acta Dermato-Venereologica Industry-funded Link to this fact
What you can do / Measured in people or real products
People with unexplained dermatitis can ask for patch testing with oxidized limonene and linalool; standard screens can miss these allergies.
Moderate evidence.
Source: Bråred Christensson 2016, Contact Dermatitis Industry-funded Link to this fact
What you can do / Review of other studies
If you have unexplained eczema, ask for patch testing that includes oxidized limonene and linalool, now recommended for the European baseline series.
Moderate evidence.
What you can do / Measured in people or real products
If you have eczema, ask for patch testing that includes oxidized linalool and limonene: they are not in every standard test series, so the allergy can be missed.
Moderate evidence: The authors say more clinical-relevance data are needed before routine screening.
What you can do / Measured in people or real products
If you are diagnosed with oxidized-linalool contact allergy, avoiding products listing linalool or fragrance/parfum is worth doing even at low concentrations, since repeated use at product-realistic doses reproduced dermatitis in a clinical trial, and most participants who had already stopped using linalool-containing products reported their dermatitis improved.
Moderate evidence: Self-reported improvement on avoidance (4 of 5) is not blinded or controlled; the ROAT elicitation data (the stronger evidence) show reactions down to 0.3% oxidized linalool.
Source: Andersch Björkman 2014, Contact Dermatitis Link to this fact
What you can do / Measured in people or real products
If you have a confirmed (not just borderline) positive patch test to limonene hydroperoxides, avoiding products with appreciable oxidized/aged limonene is well supported: realistic product-level doses reliably triggered a reaction in this group.
Moderate evidence: Applies to confirmed reactors; a borderline patch-test result is much weaker evidence of true allergy.
What you can do / Measured in people or real products
People with chronic, treatment-resistant hand eczema and a history of reacting to scented products can ask their dermatologist for patch testing beyond the standard fragrance mix, including citral, Lyral, hydroxycitronellal and oxidized limonene/linalool.
Moderate evidence: Based on one clinical population's reaction pattern (Heydorn 2003); a dermatologist should tailor markers to local product exposure.
Source: Heydorn 2003, Contact Dermatitis Industry-funded Link to this fact
What you can do / Review of other studies
Close fragranced products after use and discard them about a year after opening to limit exposure to oxidized allergens.
Weak evidence.
Caveats
Expert advice; no study tests whether it reduces dermatitis. The assumed mechanism (in-bottle oxidation during storage) has now failed two industry market surveys rather than one: Kern 2014 (fine fragrances, antiperspirants, 9 months accelerated storage) and Natsch 2019 (104 products including creams and lotions, two fine fragrances tracked 3-6 years at room temperature) both found no hydroperoxide accumulation with age or storage time. The advice may still be reasonable for essential oils and raw materials (which do carry hydroperoxide, e.g. lavandin ~220 ug/g), just not via this specific in-bottle mechanism for finished consumer products. Both studies are industry-funded (IDEA consortium: Givaudan, Firmenich, IFF, IFRA) and not independently replicated, and say nothing about essential oils, raw materials or product categories outside fine fragrances/antiperspirants/creams/lotions. Kern 2014 and Natsch 2019 are both industry studies (Givaudan / IDEA consortium) with Natsch as a co-author on both, so they are not independent replications of each other.
Source: Pastor-Nieto 2021 (Klaschka 2010), Current Treatment Options in Allergy Link to this fact
Information, not medical advice. See also: myths we won’t tell you.