Benzisothiazolinone

What is Benzisothiazolinone?

Benzisothiazolinone is a synthetic heterocyclic compound from the isothiazolinone class, typically appearing as a colorless to pale yellow liquid or powder with high water solubility. Developed as a broad-spectrum biocide, it finds common application in water-based cosmetic products like lotions, gels, shampoos, and cleansers at trace levels. It works by penetrating microbial cell walls and reacting with essential protein thiol groups, disrupting enzymes vital for bacterial, yeast, and fungal metabolism, thereby halting growth and spoilage. This mechanism ensures formula integrity against contamination throughout shelf life and consumer use. Regulatory evaluations focus on its potency, permitting limited concentrations in specific product types while highlighting needs for patch testing in formulations.

Comedogenic Rating 0/5 Low risk of clogging pores
EWG Safety Rating 6 View on EWG →

Roles in Formulation

This ingredient serves the following purposes in cosmetic formulations:

Preservative
Protects the product from microbial contamination during storage and use, helping maintain safety, stability, and shelf life.
Antimicrobial agent
Helps limit growth of bacteria and other microbes on skin or in the formula; may be used for product protection, odor control, or targeted antimicrobial effects.

Benefits

Prevents microbial growth to maintain product freshness.

Broad-spectrum action against bacteria, fungi, and yeasts.

Supports stability in water-rich skincare formulas.

Who It's For

A quick guide for who this ingredient may suit (and who should be cautious).

Who May Benefit Who Should Avoid
Individuals using rinse-off products without sensitivity issues.
Those with sensitive or reactive skin.
Users seeking effective preservation in daily cleansers.
Individuals with known contact allergies.
People with normal skin tolerance to common preservatives.
People prone to dermatitis from preservatives.

Safety Notes

  • Associated with potential for allergic skin reactions.
  • High hazard rating for immunotoxicity concerns.

Frequently Asked Questions about Benzisothiazolinone

What does benzisothiazolinone do in skincare?

It acts as a preservative to inhibit microbes, keeping water-based products safe and stable.

Is benzisothiazolinone irritating?

It poses a high risk for skin sensitization and allergic reactions in some users.

Where is it commonly used?

In rinse-off products like shampoos, lotions, and cleansers at very low levels.