Benzisothiazolinone; 1,2-Benzisothiazoline-3-One(in 434 products)
1. Antimicrobial Preservative - Actively kills and inhibits the growth of unwanted microorganisms which may be harmful.
2. Antioxidant - Reduces oxidation to prevent the formation of free radicals which may be harmful to health.
3. Drug / Medicine - Used to treat, alleviate, cure or prevent sickness. As officially declared by a governmental drug/medicine regulatory body
4. Fragrance / Fragrance Component - Provides or enhances a particular smell or odor.
5. Preservative - Prevents and inhibits the growth of unwanted microorganisms which may be harmful
Benzisothiazolinone (BIT) is widely used in home cleaning and car care products; laundry detergents, stain removers, and fabric softeners.
It is a known human immune system toxicant, and also is classified as an irritant for skin, eyes, and lungs. It is widely used as an active ingredient of many home cleaning products, paints, varnishes, adhesives, washing agents, plasters, sealants, and fabric treatments. 
Benzisothiazolinone or “1,2-Benzisothiazolin-3-one (BIT) (CAS no. 2634-33-5) is a biocide and fungicide that is widely used in paint and varnishes, but also in household cleaning products such as laundry detergents, and in agriculture pesticide formulations. BIT is the most frequently used isothiazolinone on the Danish market…”. . In a study, “Three hundred and ninety-two patients were tested with 0.05% BIT and 183 with 0.1% BIT; 27 patients had positive patch test reactions to BIT (0.05% and/or 0.1%)...Of the patients with positive patch test reactions to BIT, 85% were men, and 67% had hand eczema; 63% of cases were occupationally related.”  “Almost all publications on contact allergy to BIT are case reports. BIT is considered to be a weak to moderate contact allergen and less sensitizing than MI (methylisothiazolinone)”.  “Lundov et al. found a prevalence of 0.2% positive patch test reactions among 2411 patients tested consecutively with 0.1% BIT aq., and BIT is therefore considered to be a rare allergen, despite its frequent use in water-based paints.” 
In a separate study, "BIT concentrations below the following concentrations of 0.0075%, 0.035%, 0.035%, 0.021% [roughly 75-350ppm] in sunscreen, laundry detergent, dish soap, and spray cleaner, respectively, are unlikely to induce skin sensitization.”  "A pilot study consisting of bulk sample analysis of one representative product from each category labelled as containing BIT, and found BIT concentrations of 0.0009% and 0.0027% for sunscreen and dish soap, respectively.”  “BIT was not detected in the laundry detergent and spray cleaner products above the limit of detection of 0.0006%. Based on publicly available data for product formulations and our results, we were able to establish that cleaning products and sunscreens likely contain BIT at concentrations similar to or less than our calculated maximal safe concentrations and that exposures are unlikely to induce skin sensitization in most users.” 
Modelling aggregate consumer exposure to benzisothiazolinone “…using the newly proposed Probabilistic Aggregated Consumer Exposure Model–Kinetic, Dermal (PACEM-KD) by combining the reported individual use patterns for HC&PCP in Switzerland (N = 669 (558 adults), ages 0–91) with isothiazolinone concentrations measured in products used by the individual person.”  It was found that BIT had an exposure of 15.4 ng/cm2 on the palms of subjects (99th percentile).  Where “major sources of exposure to BIT included all-purpose cleaners, dishwashing detergent, and kitchen cleaner”.  “A Quantitative Risk Assessment (QRA) for BIT using Sensitization Assessment Factors (SAFs) indicates that around 1% of the Swiss population is at risk to be sensitized by BIT in cosmetics and household chemicals.”  “In 2012, BIT was classified as unsafe for use in PCPs due to its sensitizing potential and according to Annex V in Regulation EC. No. 1223/2009 BIT and OIT are not allowed in PCP (personal care product) formulations (Regulation EC, 2009).”  However, 1Source has not found any evidence that BIT has not been allowed for use in PCPs. BIT is not included in CosIng Annex V (as of April 2021), and Annex V is a compilation of ingredients which are allowed for use in PCPs. Ingredients prohibited in PCPs will be listed in Annex II.
“Benzisothiazolinone (1,2-benzisothiazolin-3-one or BIT) is an antimicrobial agent used as a preservative in multiple water-based solutions, such as glues, cleaning agents, polishes, paints, varnishes, and hardeners”.  “It may occasionally be present in PVC gloves and (imitation) leather shoes.”  “Also, in 2012, the Scientific Committee on Consumer Safety expressed its concerns about its sensitizing properties, which are similar to those of methylisothiazolinone; hence, use of BIT in cosmetics has not been considered to be safe.”  Again, 1Source has not found any evidence that BIT has not been allowed for use in PCPs.
Benzisothiazolinone is also commonly used in water-based paints. In a sample of 71 different types of wall paints, “BIT [was found] in 95.8% (n = 68), ranging from 0.1 to 462.5 ppm”. “Paints purchased in Denmark and Sweden contained especially high concentrations of BIT.”  “Benzisothiazolinone (BIT), with a much longer history of use, is the leading preservative in Swedish paint and is incorporated in most water-based Swedish paints and putties at concentrations of up to 0.025%.” 
Similar to other isothiazolinones, BIT undergoes photodegradation in the presence of UV light. “BIT is also used in paper-based jointing but it degrades during sunlight exposure losing its biocidal efficiency.”  “According to the European Chemicals Agency, BIT is very toxic to aquatic life, causes eye damage and skin irritation.”  “The UV-VIS irradiation of an aqueous solution of benzisothiazolinone led to the formation of fourteen photoproducts…”  “The photoproducts including a phenolic or a sulfino group or both functions were found potentially more toxic than benzisothiazolinone.” 
Overall, benzisothiazolinone appears to be somewhat more penetrative than methylisothiazolinone, where it can trigger contact allergy reactions at lower concentrations. As of April 2021, there has been no evidence of BIT being banned by CosIng Annex II or for use in PCPs. BIT is also commonly used in Danish and Swedish water-based paints. Although it undergoes photodegradation naturally, it is "very toxic to aquatic life" and the photoproducts formed from the degradation can potentially be more problematic.
1. PubChem: https://pubchem.ncbi.nlm.nih.gov/compound/17520
2. Contact allergy to 1,2-benzisothiazolin-3-one. (Contact Derm., 75(5), 324–326. doi:10.1111/cod.12570)
3. Estimation of the safe use concentrations of the preservative 1,2-benzisothiazolin-3-one (BIT) in consumer cleaning products and sunscreens. (Food Chem. Toxicol., 56(), 60–66. doi:10.1016/j.fct.2013.02.006)
4. Aggregate consumer exposure to isothiazolinones via household care and personal care products: Probabilistic modelling and benzisothiazolinone risk assessment. (Environ. Int., 118(), 245–256. doi:10.1016/j.envint.2018.05.047)
5. Occupational allergic contact dermatitis caused by benzisothiazolinone in printing ink and soap. (Contact Derm., 76(1), 51–53. doi:10.1111/cod.12642)
6. Methylisothiazolinone and benzisothiazolinone are widely used in paint: a multicentre study of paints from five European countries. (Contact Derm., 72(3), 127–138. doi:10.1111/cod.12322)
7. Skin disease and contact sensitivity in house painters using water-based paints, glues and putties. (Contact Derm., 32(1), 39–45. doi:10.1111/j.1600-0536.1995.tb00839.x)
8. Photodegradation of benzisothiazolinone: Identification and biological activity of degradation products. (Chemosphere, 240(), 124862–. doi:10.1016/j.chemosphere.2019.124862)
1. EU Scientific Committee on Consumer Safety
- https://ec.europa.eu/health/archive/ph_risk/committees/sccp/documents/out289_en.pdf - https://ec.europa.eu/health/scientific_committees/consumer_safety/docs/sccs_o_099.pdf
2. CANADA Natural Health Products Ingredients Database 
3. International Fragrance Association Transparency List 
Safety and Hazards (UN GHS):
1. Harmful if swallowed (H302)
2. Causes skin irritation (H315)
3. May cause an allergic skin reaction (H317)
4. Causes serious eye damage (H318)
5. May cause damage to organs (H371)
6. Very toxic to aquatic life (H400)
7. Very toxic to aquatic life with long lasting effects (H410)
Potential Health Concerns For:
1. Dermatitis, Allergic Contact (PubMed ID:26795242)
2. Dermatitis, Contact (PubMed ID:25724174)
3. Poisoning (PubMed ID:28728110)