- What it can be used for
- Kills or slows microbes (the functions the EU ingredient database, CosIng, lists for it; a product may use it for any of them)
- CAS number
- 2634-33-5
Why it’s flagged
Classified as a skin sensitizer (may cause an allergic skin reaction).
- Skin Sens. 1A (H317). Source: EU CLP Regulation, Annex VI harmonized classification
EU hazard statement H317: may cause an allergic skin reaction.
What the research says
- Citric acid, methylisothiazolinone, phenoxyethanol, benzisothiazolinone, and the fragrance chemical geraniol were the five most commonly listed biocidal active substances in a 2016 scan of German household products, appearing on 859, 471, 409, 357, and 281 products respectively out of 2,963 scanned. Moderate evidence. Wieck 2016
- Certain hormone-disrupting chemicals recur together on the same product's ingredient list more often than chance: benzisothiazolinone with hexyl cinnamaldehyde in synthetic detergents, and the fragrance chemical Lilial (butylphenyl methylpropional) with citronellol in fabric softeners, identified by mining co-occurrence patterns across thousands of Korean household products. Moderate evidence. Lee & Ji 2022
- Because hormone-disrupting chemicals cluster by product type, cleaners, synthetic detergents, fabric softeners, air fresheners, and deodorants are the household product categories where checking for isothiazolinone preservatives (such as benzisothiazolinone) and fragrance chemicals (such as hexyl cinnamaldehyde, geraniol, and citronellol) is likely to be most worthwhile. Moderate evidence. Lee & Ji 2022
About ingredients flagged like this one:
- In a survey of 187 US pediatric personal-care products, preservatives (57.8% of products) were a more common source of contact allergens than fragrance (29.4%), even though the products were being screened specifically for hypoallergenic/fragrance-related marketing claims. Moderate evidence. Hamann 2015
Each finding shows its evidence grade. See every graded fact or how we grade.
What this page can’t tell you
These lists describe what a substance can do, its hazard. The risk from one product depends on how much is in it and how you use it, and the label doesn’t say how much.
Not being on a list doesn’t make an ingredient safe. It may never have been assessed.
Check your products
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Flagged the same way
Official lists checked September 2026. Spotted a mistake? Tell us.