Proposition 65 NSRL: Carcinogen Limits, Exposure, and Exceptions

The Proposition 65 No Significant Risk Level, or NSRL, is a daily exposure ceiling for a listed cancer-causing chemical. Stay at or below it and you owe no Proposition 65 warning, and you have a safe harbor against both government enforcement and private lawsuits.¹ The number is set at a level that would cause no more than one additional cancer case per 100,000 people exposed daily for 70 years. That is a conservative bar by design, and understanding how it works is the difference between routine compliance and an expensive certificate-of-merit letter arriving in the mail.

What the NSRL Is and What It Covers

Proposition 65 requires any business with ten or more employees to give a clear and reasonable warning before exposing a person to a listed chemical.² The NSRL is the safe harbor number that lets you skip that warning for a listed carcinogen. The regulatory basis is Title 27 of the California Code of Regulations, Section 25701.³

The NSRL covers carcinogens only. Chemicals listed for reproductive toxicity use a separate threshold called the Maximum Allowable Dose Level, or MADL.⁴ Some chemicals appear on both lists, so a single substance may force you to meet both thresholds. Lead is the standard example: it carries a 15 μg/day NSRL for cancer risk but a 0.5 μg/day MADL for reproductive toxicity, and the lower number is what controls in practice.

How the Number Is Set

Every NSRL is built backward from the one-in-100,000 risk goal. Researchers pull data from animal studies or human epidemiology, apply dose-response models to estimate cancer potency, and use conservative assumptions at each step so uncertainty tips toward protecting the public. The result is expressed in micrograms per day.

Two features of the calculation are worth pinning down. First, “lifetime” means 70 years of daily exposure. That figure is written directly into the exposure formulas in Section 25721.⁵ Second, the regulations allow adjusted levels in narrow situations where sound public health reasoning supports a different benchmark, such as chemicals formed during cooking that makes food safe to eat, chlorine disinfection under federal and state drinking water rules, and government-supervised cleanups.¹ For most businesses, though, the published NSRL is the number that matters.

Measuring Your Product’s Exposure Against It

Knowing the NSRL for a chemical is only half the compliance question. You also have to calculate the daily exposure your product actually creates and compare it against the threshold. Section 25721 spells out the default assumptions.

For a typical adult, the defaults are two liters of drinking water per day, 20 cubic meters of inhaled air per day, and a 70-year lifespan.⁵ For a consumer product, the regulation directs you to use the average intake rate for people who actually use that product category, not a per-capita figure spread across every Californian. If only a fraction of the population uses a product, the exposure assessment focuses on real users. You can substitute product-specific data when the science supports it, but most compliance work starts from these defaults.

Courts have accepted that exposure can be averaged over time rather than measured on a single peak day, which matters for products used intermittently.⁵

Where to Find Published NSRLs and Sample Values

The Office of Environmental Health Hazard Assessment maintains the official list. OEHHA has published more than 300 safe harbor levels across carcinogens and reproductive toxins, and the values are updated as new science emerges.⁴ Check the current list rather than relying on a number you looked up years ago.

A few examples show how widely the values spread:

Acrylamide: 0.2 μg/day. This tight threshold drives Proposition 65 suits against coffee, potato chip, and baked-goods sellers.
Inorganic arsenic by inhalation: 0.06 μg/day.
Lead by the oral route: 15 μg/day NSRL, though the 0.5 μg/day MADL for reproductive toxicity is the effective limit.
Formaldehyde gas: 40 μg/day.
Benzene: 6.4 μg/day oral, 13 μg/day inhalation.
Glyphosate: 1,100 μg/day, one of the more permissive levels.

All figures are micrograms per day.⁴

When No NSRL Has Been Published

Plenty of listed carcinogens have no OEHHA-published NSRL. The safe harbor still exists on paper, but you have to build the number yourself using the same one-in-100,000 methodology the state uses.¹ OEHHA itself calls determining anticipated exposure “very complex” and recommends consulting a qualified professional.⁶

In practice that means a toxicologist or specialized consultant, dose-response data, and a written risk assessment that can survive a courtroom challenge. There is no government pre-approval for a privately developed NSRL. The quality of the science and the credibility of the expert are your only defenses if someone sues.

Two failure modes are common. Some companies skip the assessment and apply an unnecessary warning, which OEHHA discourages because it dilutes real warnings. Others produce a thin assessment that collapses under litigation. If your product category depends on an ingredient that lacks a published NSRL, paying for a rigorous assessment upfront is almost always cheaper than defending a suit later.

Proving the Safe Harbor Applies

Proposition 65 puts the burden of proof on the business. Once a plaintiff shows that a listed chemical is present, the company has to affirmatively demonstrate that exposure falls below the NSRL (or the MADL, for a reproductive toxin).² Waiting for the other side to prove danger is not the framework the statute uses.

That means the paperwork has to exist before the notice arrives. If a published NSRL applies, keep an exposure assessment on file showing your product falls below it. If no published NSRL applies, keep both a risk assessment and an exposure assessment. Use average users, not extreme cases, and document the methodology.

The Naturally Occurring Exception for Food

A separate safe harbor sits in Section 25501: consuming a food does not count as an exposure to a listed chemical if the chemical is a natural constituent of the food or is present only because the food absorbed it from its natural environment.⁷ Minerals absorbed from soil or toxins produced by fungi on crops are the classic examples.

The exception is narrower than it first looks. The chemical qualifies as naturally occurring only to the extent it was not introduced by human activity. If contamination is partly natural and partly from pesticide use or industrial runoff, only the natural share is covered. Plowing, planting, and irrigating are not treated as “human activity” for this purpose, but adding chemicals to irrigation water is.⁷

The producer also has to use good manufacturing practices to reduce the chemical to the lowest level currently feasible. The defense extends to non-food consumer products when the listed chemical came from a naturally occurring chemical in a food ingredient used during manufacturing.⁷

What Happens If You Miss the Safe Harbor

Most Proposition 65 enforcement is private. The statute lets private citizens and organizations sue for violations, and a whole plaintiffs’ bar has grown up around that mechanism. Before filing, the private enforcer has to serve a 60-day notice of the alleged violation on the Attorney General, the relevant local prosecutor, and the business.⁸

For failure-to-warn claims, the notice must include a certificate of merit. The attorney certifies they consulted someone with relevant expertise, reviewed the facts and exposure data, and concluded the case has a reasonable basis.⁸ If neither the Attorney General nor a local prosecutor takes the case within 60 days, the private plaintiff can proceed.

Civil penalties can reach $2,500 per violation per day. Courts weigh severity, number of violations, economic effect on the violator, good-faith compliance efforts, and deterrent value when setting the amount.⁸ Most cases settle, and settlements routinely add attorney’s fees plus injunctive relief requiring reformulation or new warnings. The fees alone often exceed the statutory penalty.

If exposure exceeds the NSRL and no other defense applies, you have to provide a clear and reasonable warning in one of the safe harbor formats. The label needs a yellow triangle with a black exclamation point, sized at least as tall as the word “WARNING.” A black-and-white version works on labels not printed in color.⁹

OEHHA amended the warning rules effective January 1, 2025. The short-form warning now has to include at least one chemical name. Businesses using the older short-form format have a three-year transition period that closes at the end of 2027, so packaging and signage updates should already be underway.¹⁰

Grace Period for Newly Listed Chemicals

When OEHHA adds a chemical to the Proposition 65 list, the warning requirement does not kick in immediately. You have 12 months from the listing date before the obligation to warn attaches. The separate discharge prohibition, which bars releasing listed chemicals into drinking water sources, kicks in 20 months after listing.¹¹

The clock starts on the listing date, not the date you notice it. If you sell into California, build a routine for tracking OEHHA additions so the grace period is used for testing, reformulation, or labeling rather than eaten up before anyone realizes a new chemical has landed on the list.

1
Legal Information Institute. California Code of Regulations 27 CCR 25703 – Quantitative Risk Assessment
2
California Legislative Information. California Health and Safety Code HSC 25249-6
3
Legal Information Institute. California Code of Regulations 27 CCR 25701 – No Significant Risk Level
4
Office of Environmental Health Hazard Assessment. Proposition 65 No Significant Risk Levels NSRLs and Maximum Allowable Dose Levels MADLs
5
Legal Information Institute. California Code of Regulations 27 CCR 25721 – Level of Exposure to Chemicals
6
Office of Environmental Health Hazard Assessment. Businesses and Proposition 65
7
Legal Information Institute. California Code of Regulations 27 CCR 25501 – Exposure to a Naturally Occurring Chemical in a Food
8
California Legislative Information. California Health and Safety Code HSC 25249-7
9
Proposition 65 Warnings Website. Where Can I Get Information on the Warning Symbol
10
Office of Environmental Health Hazard Assessment. Proposition 65 Clear and Reasonable Warnings – Safe Harbor Methods and Content
11
Office of Environmental Health Hazard Assessment. Appendix A – The Safe Drinking Water and Toxic Enforcement Act of 1986 Proposition 65 A Summary