California’s Proposition 65 safe harbor levels are daily exposure thresholds set by the Office of Environmental Health Hazard Assessment (OEHHA) for each listed chemical. If a business can show that normal use of its product exposes a consumer to less than the threshold for a given chemical, no warning is required, even though the chemical is present. Two kinds of numbers do this work: No Significant Risk Levels (NSRLs) for carcinogens and Maximum Allowable Dose Levels (MADLs) for reproductive toxicants.
The Two Types of Thresholds
Which number applies depends on why the chemical is on the Proposition 65 list in the first place. Some chemicals are listed only as carcinogens, some only as reproductive toxicants, and some for both. OEHHA assigns a separate safe harbor level for each endpoint, and a product has to clear every number that applies to it.
No Significant Risk Level (NSRL) for Carcinogens
For a chemical listed as a carcinogen, the threshold is the daily exposure calculated to produce no more than one excess case of cancer in a population of 100,000 people over a lifetime of exposure.1Cornell Law School. California Code of Regulations Title 27 Section 25703 – Quantitative Risk Assessment “Lifetime” means 70 years of daily contact at that dose. The resulting number is deliberately conservative and is often measured in fractions of a microgram per day.
Maximum Allowable Dose Level (MADL) for Reproductive Toxicants
For a chemical listed for reproductive harm, regulators start with the highest dose at which the chemical produced no observable reproductive effect in human or animal studies, then divide that dose by 1,000.2Cornell Law School. California Code of Regulations Title 27 Section 25801 – General That thousand-fold safety margin is built to protect the most sensitive populations, including pregnant women and developing children, by setting the allowable exposure far below any level where harm has ever been observed in a study.
Examples
The gap between the cancer number and the reproductive number for the same chemical can be dramatic, and which one binds is not always obvious.3Office of Environmental Health Hazard Assessment. Proposition 65 No Significant Risk Levels (NSRLs) and Maximum Allowable Dose Levels (MADLs)
- Lead: NSRL of 15 micrograms per day (oral, cancer); MADL of 0.5 micrograms per day (reproductive harm). The reproductive number is 30 times stricter, so lead warnings are almost always triggered by the MADL.
- Acrylamide: NSRL of 0.2 micrograms per day (cancer); MADL of 140 micrograms per day (reproductive harm). Here the cancer number binds, which matters for coffee, baked goods, and fried foods where acrylamide forms during cooking.
- Cadmium: NSRL of 0.05 micrograms per day (inhalation, cancer); MADL of 4.1 micrograms per day (oral, reproductive harm). The route of exposure changes which number applies.
Not every listed chemical has a published safe harbor level. For chemicals without one, a business must either conduct its own risk assessment or provide a warning. OEHHA publishes the full table of established NSRLs and MADLs, and it is worth checking before paying for custom testing or a toxicology opinion.
Measuring Whether a Product Exceeds the Level
Knowing a listed chemical is in a product is not enough to answer the compliance question. The business claiming a safe harbor exemption has to quantify the daily dose a person actually absorbs during normal use, and then compare that dose to the NSRL or MADL.
Two steps get you there. First, lab testing identifies the concentration of the chemical in the product, typically in parts per million or parts per billion. Second, exposure modeling translates that concentration into a daily dose using standardized assumptions about how the product is used: how long skin contact lasts, how much of a food someone eats, whether the substance is inhaled or swallowed, how many times per day the product is used. The regulations supply the assumptions, but a toxicologist or environmental consultant typically runs the calculation.
If modeled daily exposure stays below the relevant threshold, no warning is owed. If it exceeds the threshold, a warning is required. Keep the lab results and the exposure assumptions on file. The statute does not explicitly mandate records, but those records are the primary defense if a private enforcer serves a notice, because the enforcer’s expert will run the same calculations and challenge every input.
The Naturally Occurring Exception for Food
Food producers have an additional avenue. A chemical is treated as “naturally occurring” if it is a natural constituent of the food or is present solely because the food absorbed it from the environment, such as minerals taken up from soil created by natural geologic processes.4Cornell Law School. California Code of Regulations Title 27 Section 25501 – Exposure to a Naturally Occurring Chemical in a Food Only the naturally occurring portion counts. Any amount added by human activity is still measured against the regular safe harbor level.
The exception has conditions. The producer must use quality control measures to reduce the natural contaminant to the lowest level currently feasible. Routine agricultural practices like plowing and irrigating are allowed, but adding chemicals to irrigation water is not. The producer also needs reliable data on the natural background level of the chemical in the growing region. Without that data, the defense fails.
What Happens When a Product Exceeds the Level
If exposure exceeds the applicable threshold and no exemption fits, the business must provide a “clear and reasonable warning” before the exposure occurs.5California Legislative Information. California Health and Safety Code Section 25249.6 – Required Warning Before Exposure to Chemicals Known to Cause Cancer or Reproductive Toxicity The detailed formatting rules sit in Title 27 of the California Code of Regulations.
What the Warning Must Say
A compliant safe harbor warning includes four elements:6Cornell Law School. California Code of Regulations Title 27 Section 25603 – Consumer Product Exposure Warnings
- A warning symbol: a black exclamation point inside a yellow equilateral triangle with a bold black outline, placed to the left of the warning text and at least as tall as the word “WARNING.” Black-and-white is acceptable where the label is not printed in color.
- The word “WARNING” in all capital letters and bold. “CA WARNING” or “CALIFORNIA WARNING” are also accepted.
- At least one chemical name. If the product triggers warnings for both cancer and reproductive toxicity, the warning must name at least one chemical for each category, unless a single chemical covers both.7Cornell Law School. California Code of Regulations Title 27 Section 25601 – Methods and Content
- The type of risk: cancer, reproductive harm, or both.
How the Warning Must Reach the Consumer
For physical products, an on-product label is the most common approach, and the warning must be prominent and legible compared to other text on the packaging. Point-of-purchase signs at a retailer also work if they are clearly visible before checkout. For online sales, the warning must appear on the product display page itself, or a clearly marked hyperlink using the word “WARNING” must be visible before the consumer completes the purchase.8Proposition 65 Warnings. Frequently Asked Questions for Businesses Burying it in a terms-of-service page or sending it in a post-purchase email does not satisfy the rule.
Products with limited label space can use an abbreviated “short-form” warning, but as of January 1, 2025, the short-form warning must include at least one chemical name.9Office of Environmental Health Hazard Assessment. Proposition 65 Clear and Reasonable Warnings – Safe Harbor Methods and Content Businesses already using the older short-form format have a three-year transition period to update their labels.
Who Does Not Have to Comply
Proposition 65 reaches any business that exposes someone in California to a listed chemical, including companies headquartered outside the state. Manufacturing in Oregon, importing from overseas, or shipping from a warehouse in Texas does not take you outside the law if the product ends up in California hands. Online sellers are covered.
Three categories are carved out of the statutory definition of a “person in the course of doing business”:10California Legislative Information. California Health and Safety Code Section 25249.11
- Businesses with fewer than 10 employees, which are fully exempt from both the warning requirement and the discharge prohibition.
- Government agencies at the federal, state, county, city, and district level, including their departments.
- Public water systems as defined in state law.
There is also a built-in grace period when OEHHA lists a new chemical. Warning requirements do not begin until 12 months after the listing date, and the discharge prohibition does not begin for 20 months.11California Legislative Information. California Health and Safety Code Section 25249.10 That window is the time to test, reformulate, or add a label before enforcement risk starts.
The underlying chemical list is published and maintained by OEHHA. It contains more than 850 entries covering pesticides, industrial solvents, food-processing byproducts, and naturally occurring minerals, and new chemicals are added on a rolling basis.12Office of Environmental Health Hazard Assessment. The Proposition 65 List If a chemical is not on the list, Proposition 65’s warning and discharge rules do not apply to it at all.
What a Miss Costs
Enforcement comes mainly through private lawsuits. Before filing suit, a private enforcer serves a 60-day notice on the alleged violator, the Attorney General, and the relevant local prosecutor, identifying the chemicals, the product, the route of exposure, and the time period at issue.13California Legislative Information. California Health and Safety Code Section 25249.7 A notice alleging failure to warn must include a certificate of merit stating that the noticing party consulted with someone with relevant expertise and concluded the case has merit.14Cornell Law School. California Code of Regulations Title 11 Section 3101 – Contents The 60-day window is also the main window for settlement.
Civil penalties run up to $2,500 per day per violation.15State of California – Department of Justice – Office of the Attorney General. Frequently Asked Questions – View All Each product sold without a required warning can be counted as a separate violation, so the arithmetic escalates fast at any real sales volume. Courts can also order the business to stop the violation going forward, which in practice means reformulating, adding warnings, or pulling the product from California. Settlements typically include attorney’s fees and costs on top of penalties, and the fee component often exceeds the penalty itself. Reported private enforcement settlements have historically averaged around $42,000, with wide variation by chemical, volume, and duration.16State of California – Department of Justice – Office of the Attorney General. Proposition 65 Enforcement Reporting For a small company receiving its first notice, the combined exposure is often large enough to threaten the business, which is why the exposure calculation against the safe harbor level is worth getting right before the product ships.