Proposition 65 Chemical List: Safe Harbor Levels and Business Duties

The Proposition 65 chemical list is California’s official registry of substances the state has identified as causing cancer, birth defects, or other reproductive harm. It is maintained by the Office of Environmental Health Hazard Assessment (OEHHA) under the Safe Drinking Water and Toxic Enforcement Act of 1986, and it now contains more than 900 chemicals, from industrial solvents and pesticide ingredients to heavy metals like lead and cadmium and byproducts of combustion like diesel exhaust.¹ The Governor is required by statute to revise and republish the list at least once a year, and in practice OEHHA adds chemicals throughout the year as new evidence comes in.²

What’s on the List

Every entry falls into one or both of two categories: chemicals known to cause cancer, and chemicals known to cause birth defects or other reproductive harm. Many substances appear under both headings because they carry both risks.³

The scope is deliberately broad. You’ll find synthetic industrial chemicals, pesticide active ingredients, pharmaceutical compounds, heavy metals, manufacturing solvents, and combustion byproducts. Some are substances most people never encounter directly. Others turn up routinely in food, consumer products, building materials, and vehicle exhaust, which is why Prop 65 warnings appear on such a wide range of items.

How to Look Up a Chemical

OEHHA publishes the complete list on its website in downloadable spreadsheet and PDF formats. The files let you filter by chemical name, the date it was listed, and whether the listing is for cancer, reproductive harm, or both.³

For a faster check on a single substance, the state’s warnings site at P65Warnings.ca.gov has a search tool that returns whether a chemical is listed, its category, and common sources of exposure.⁴ If you need exposure thresholds — the levels below which no warning is required — those are published in separate NSRL and MADL tables, updated as new levels are adopted.⁵

How Chemicals Get Added

There are four separate paths onto the list.⁶

Two independent scientific committees — the Carcinogen Identification Committee and the Developmental and Reproductive Toxicant Identification Committee — review toxicological evidence and can vote to add a chemical when the evidence clearly demonstrates harm. Each meets at least once a year.
The list must include chemicals identified in Labor Code Section 6382(b)(1), which incorporates substances classified as carcinogenic by the World Health Organization’s International Agency for Research on Cancer.
A designated authoritative body can trigger a listing when it formally identifies a chemical as harmful. These include the U.S. EPA, the FDA, the National Institute for Occupational Safety and Health, the National Toxicology Program, and IARC.⁷
A chemical is added when a state or federal agency formally requires it to be labeled as causing cancer or reproductive harm.

Removal is much harder. A member of the public, a state agency, or an expert committee can petition OEHHA to reconsider a listing, but OEHHA will only move forward if there has been a substantial change in the scientific evidence since the original decision. If the agency agrees to reconsider, it publishes a notice, opens a 60-day public comment period, and sends the materials to the expert committee for a final vote at a public meeting.⁸ Delistings are rare. The original listing already required a clear scientific showing, so reversing it requires a comparable one.

Safe Harbor Levels: When a Listing Actually Triggers a Duty

Being on the list does not, by itself, mean every use of a chemical requires a warning. OEHHA has established exposure thresholds for many listed chemicals, and if a business can show exposure stays below the relevant threshold, no warning is required.

For cancer-causing chemicals, the threshold is the No Significant Risk Level (NSRL), the daily intake estimated to produce no more than one additional cancer case in a population of 100,000 people exposed every day over a lifetime.⁹ For reproductive toxicants, the threshold is the Maximum Allowable Dose Level (MADL), calculated by taking the highest dose at which no reproductive harm was observed in testing and dividing by 1,000. That thousandfold safety margin accounts for differences between test animals and humans, variation within the human population, and uncertainty in the underlying data.¹⁰

Two chemicals that show up often in enforcement actions illustrate the scale:

Lead: NSRL of 15 micrograms per day by oral exposure; MADL of 0.5 micrograms per day. The much lower reproductive threshold is a large part of why lead warnings are so common.
Inorganic arsenic: NSRL of 10 micrograms per day for oral exposure and 0.06 micrograms per day for inhalation exposure.

Not every listed chemical has an established safe harbor level. When no NSRL or MADL exists, the business has to determine on its own whether an exposure requires a warning, and it carries the risk if it guesses wrong.⁵

What Being on the List Means for Businesses

A listing imposes two core obligations. First, no business may knowingly discharge or release a listed chemical into water, or onto land where it will probably pass into a source of drinking water. “Source of drinking water” covers both current supplies and water identified in a regional quality control plan as suitable for domestic use.¹¹ A discharge is exempt if it won’t cause any detectable amount of the chemical to reach a drinking water source and it complies with all other applicable laws, regulations, and permits, but the business has to prove both conditions.

Second, no business may knowingly expose anyone to a listed chemical without first providing a clear and reasonable warning. The requirement reaches products sold in California, workplaces, residential buildings, restaurants, retail stores, and any other setting where a person might be exposed.¹²

Some businesses are outside the law’s reach entirely. Prop 65 does not apply to businesses with fewer than 10 employees, to government agencies at any level, or to operators of public water systems.¹³

When a new chemical is added, covered businesses get 12 months before the warning requirement takes effect for that chemical, and 20 months before the discharge prohibition takes effect.¹⁴

A safe harbor warning uses a yellow triangle with an exclamation point, the word “WARNING” in bold capitals, at least one named chemical, and a reference to P65Warnings.ca.gov. A typical lead warning reads: “WARNING: This product can expose you to lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm.” Amended regulations effective January 1, 2025, closed the option of a short-form warning that named no specific chemical. Short-form labels must now include at least one chemical name, and businesses using the old format have until January 1, 2028, to transition.¹⁵

Why the List Drives So Much Litigation

Violations of either the discharge or the warning requirement carry civil penalties of up to $2,500 per day per violation, and the daily accrual is what makes noncompliance expensive.¹⁶ The Attorney General, district attorneys, city attorneys, and certain other prosecutors can bring enforcement actions, but any person acting in the public interest can also sue, provided they give 60 days’ written notice to the alleged violator, the Attorney General, and the local prosecutor, along with a certificate of merit showing a reasonable basis for the claim. If no government prosecutor files within those 60 days, the private enforcer can proceed. Most Prop 65 cases are brought this way, and food, dietary supplements, kitchenware, and lead-containing products are among the most frequent targets.

1
Office of Environmental Health Hazard Assessment. Proposition 65
2
California Legislative Information. California Health and Safety Code HSC 25249.8
3
Office of Environmental Health Hazard Assessment. Proposition 65 Chemical List
4
Proposition 65 Warnings Website. Search Results – Proposition 65 Warnings Website
5
Office of Environmental Health Hazard Assessment. Proposition 65 No Significant Risk Levels (NSRLs) and Maximum Allowable Dose Levels (MADLs)
6
Office of Environmental Health Hazard Assessment. How Chemicals Are Added to the Proposition 65 List
7
Office of Environmental Health Hazard Assessment. Request for Information on Chemicals Under Consideration for Possible Listing via Authoritative Bodies Mechanisms
8
Office of Environmental Health Hazard Assessment. Proposition 65 – The Listing Process
9
Office of Environmental Health Hazard Assessment. No Significant Risk Level (NSRL) for the Proposition 65 Carcinogen
10
Office of Environmental Health Hazard Assessment. Proposition 65 Maximum Allowable Daily Level (MADL)
11
California Legislative Information. California Health and Safety Code HSC 25249.5
12
California Legislative Information. California Health and Safety Code HSC 25249.6
13
California Legislative Information. California Health and Safety Code HSC 25249.11
14
California Legislative Information. California Health and Safety Code HSC 25249.9
15
Office of Environmental Health Hazard Assessment. Proposition 65 – Clear and Reasonable Warnings – Safe Harbor Methods and Content
16
California Legislative Information. California Health and Safety Code HSC 25249.7