MIT, CMIT, and BIT Preservatives: What You Need to Know

Written by: Sacha Dunn

Published on October 8, 2024

Time to read 3 min

Table of contents

The Refill Movement & Safe Chemistry Why brands use them (the practical answer) Key health concern: sensitization (not just “irritation”) What regulations signal (with the right nuance) Environmental considerations (plain talk) Preservatives we use at Common Good

The Refill Movement & Safe Chemistry

Preservatives exist for a reason. Most water-based formulas need protection from microbial growth over time.

The question is which preservative system you use—and what tradeoffs you’re willing to accept.

At Common Good, we choose not to use isothiazolinone preservatives like:

Methylisothiazolinone (MIT / MI)
Methylchloroisothiazolinone (CMIT / MCI)
Benzisothiazolinone (BIT)

They’re effective. They’re also well-known skin sensitizers, and they’ve been the subject of significant regulatory attention—especially in personal care.

Why brands use them (the practical answer)

MIT/CMIT/BIT are used because they:

prevent bacteria, yeast, and mold in water-based products
work at very low concentrations
they are inexpensive
help products stay stable in real-world storage conditions

You’ll commonly see them in:

household cleaners (multi-surface sprays, dish liquids, laundry detergents)
personal care (shampoo, body wash, conditioner)

Key health concern: sensitization (not just “irritation”)

The core issue with MIT/CMIT/BIT isn’t that they’re “dirty” ingredients. It’s that they’re linked to allergic contact dermatitis (a true allergy).

That matters because:

sensitization can happen after repeated exposure
once you’re sensitized, reactions can be triggered by very small amounts later
it turns “fine for me” into “suddenly not fine” for a meaningful number of people

MIT was named “Contact Allergen of the Year” in 2013 because reported allergy rates rose sharply during widespread use.

What regulations signal (with the right nuance)

Regulations are most explicit in cosmetics, where rules differ for:

leave-on products (lotions, wipes)
rinse-off products (shampoos, body wash)

A clear example:

In the European Union, MIT is not allowed in leave-on cosmetic products, and its use is restricted in rinse-off products at low levels.

Household cleaning products are regulated under different frameworks depending on the country and product category, so you’ll see more variation. But the broader signal is consistent: regulators take sensitization risk seriously.

Environmental considerations (plain talk)

These ingredients are biocides. They’re designed to kill microbes.

As with many biocidal substances, there are legitimate concerns about aquatic toxicity depending on concentration and exposure. If you’re trying to keep your home clean and reduce unnecessary risk downstream, avoiding this preservative class is a reasonable line to draw.

Preservatives we use at Common Good

We keep formulas stable without MIT, CMIT, or BIT.

Instead, we use alternative preservative systems such as:

sodium benzoate
phenoxyethanol

We prefer a different risk profile for everyday exposure. These preservatives have been used in household and personal care products for many years and while no chemical is appropriate for all people, they are well tested and generally well tolerated by most people.

We don’t do “chemical-free.” We do Safe Chemistry: ingredients chosen for performance, with fewer obvious downsides.

Quick label-reading: what to watch for

If you’re scanning an ingredient list, look for:

Methylisothiazolinone (MIT / MI)
Methylchloroisothiazolinone (CMIT / MCI)
Benzisothiazolinone (BIT)
Preservative
Synthetic Preservative

READ ABOUT INGREDIENTS WE USE HERE→

Quick Reference Guide

The Problem: MIT, CMIT, and BIT are common, effective preservatives that are also potent skin sensitizers and allergens.

The Risk: Repeated exposure can lead to contact dermatitis and long-term sensitivity, prompting strict bans in leave-on products in the EU and other regions.

The Environmental Impact: These biocides are toxic to aquatic life even at low concentrations when washed into waterways.

The Common Good Solution: We use safe chemistry alternatives like sodium benzoate and phenoxyethanol to keep our formulas stable without the high-risk sensitization profile.