California’s Proposition 65 safe harbor levels are the daily exposure numbers a business can measure against to decide whether a product needs a warning. Stay below the level for a given listed chemical, and no warning is required even though the chemical is present. Exceed it, and a warning is required unless another exemption applies. Two separate thresholds exist: No Significant Risk Levels (NSRLs) for chemicals listed as carcinogens, and Maximum Allowable Dose Levels (MADLs) for chemicals listed as reproductive toxicants.
The Two Types of Safe Harbor Levels
Proposition 65 regulates chemicals on two separate tracks, and each track has its own threshold. The Office of Environmental Health Hazard Assessment (OEHHA) publishes both sets of numbers.
No Significant Risk Level (NSRL) for Carcinogens
For a chemical listed as a carcinogen, the NSRL is the daily exposure level 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” here means 70 years of daily contact at that dose. The result is a very conservative number, often measured in fractions of a microgram per day.
Maximum Allowable Dose Level (MADL) for Reproductive Toxicants
For a chemical listed as a reproductive toxicant, regulators start with the highest dose at which the chemical produced no observable reproductive effect in studies on humans or animals, 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 deliberately enormous. It is designed to protect the most vulnerable populations, including pregnant women and developing children, by setting allowable exposure far below any dose where harm has ever been observed.
How the Two Numbers Compare in Practice
For chemicals listed under both categories, the NSRL and MADL can differ by orders of magnitude, and the stricter of the two is what matters. A few common examples show why the comparison matters:3Office of Environmental Health Hazard Assessment. Proposition 65 No Significant Risk Levels (NSRLs) and Maximum Allowable Dose Levels (MADLs)
- Lead has an oral NSRL of 15 micrograms per day but a MADL of only 0.5 micrograms per day. The reproductive threshold is 30 times stricter, so lead warnings are almost always triggered by the MADL.
- Acrylamide has an NSRL of 0.2 micrograms per day and a MADL of 140 micrograms per day. Here the cancer number is the binding constraint, which matters for coffee, baked goods, and fried foods where acrylamide forms during cooking.
- Cadmium has an inhalation NSRL of 0.05 micrograms per day and an oral MADL of 4.1 micrograms per day. Notice that the route of exposure changes which number applies.
What Happens When a Chemical Has No Published Level
Not every listed chemical has a published NSRL or MADL. For those chemicals, there is no ready-made number to compare against, and a business must either commission its own quantitative risk assessment or provide a warning by default. OEHHA maintains the full table of established safe harbor levels, and checking it first is worthwhile before investing in a custom assessment.
Measuring Your Product Against the Level
Knowing a chemical is present in a product is not enough to invoke a safe harbor. To claim the exemption, a business must quantify how much of the chemical a person would actually absorb during normal use, then compare that daily dose to the applicable threshold.
The work runs in two steps. Lab testing identifies the concentration of the listed chemical in the product, typically reported in parts per million or parts per billion. Exposure modeling then translates that concentration into a daily dose by factoring in how the product is used: how long skin contact lasts, how much of a food someone eats, whether the substance is inhaled or swallowed, and how often the product is used. These calculations follow standardized assumptions in the regulations, but they still call for a toxicologist or environmental consultant to execute properly. This is where most enforcement problems start, because a plaintiff’s expert will run the same calculations and challenge every assumption a business made.
If modeled daily exposure stays below the relevant NSRL or MADL, no warning is required. If it exceeds the threshold, a warning is required. As a practical matter, keep detailed records of both the lab results and the exposure assumptions. The statute does not explicitly mandate record-keeping, but those records are the primary defense if an enforcement action is filed.
The Naturally Occurring Carve-Out 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 from soil formed 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 qualifies. If human activity added any amount of the chemical, that added portion is still subject to the normal safe harbor analysis.
The defense comes with conditions. The producer must use quality control measures that reduce the natural contaminant to the lowest level currently feasible. Ordinary agricultural practices like plowing and irrigating are permissible, but adding chemicals to irrigation water is not. The defense also depends on reliable data about natural background levels of the chemical in the region where the food was grown. Without that data, the defense collapses.
When Exposure Exceeds a Safe Harbor Level
If exposure crosses the 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 statute uses that general phrase. The detailed formatting rules most people associate with Proposition 65 warnings come from Title 27 of the California Code of Regulations.
A compliant safe harbor warning must include the yellow triangle warning symbol with a black exclamation point (or a black-and-white version if the label is not printed in color), the word “WARNING” in bold capital letters, at least one listed chemical name, and a statement of whether the risk involves cancer, reproductive harm, or both.6Cornell Law School. California Code of Regulations Title 27 Section 25603 – Consumer Product Exposure Warnings If the product triggers both cancer and reproductive warnings, the warning must name at least one chemical for each category unless a single chemical is listed for both.7Cornell Law School. California Code of Regulations Title 27 Section 25601 – Methods and Content
Delivery depends on the sales channel. For physical products, an on-product label is the standard approach, and the warning must be prominent and legible relative to other packaging text. Retailers can use point-of-purchase signs on shelves or at the register, provided the signs are clearly visible before the customer completes the transaction. Online sellers must place the warning on the product display page itself, or include a clearly marked hyperlink using the word “WARNING” visible before the consumer completes the purchase.8Proposition 65 Warnings. Frequently Asked Questions for Businesses A warning buried in terms of service or a post-purchase email does not count.
The Cost of Getting the Analysis Wrong
Proposition 65 is enforced primarily through private lawsuits. Any private party acting “in the public interest” can serve a 60-day notice on the alleged violator, the Attorney General, and the relevant local prosecutor, and if no government office files its own action within 60 days, the private enforcer can sue.9California Legislative Information. California Health and Safety Code Section 25249.7 Civil penalties run up to $2,500 per day per violation, and each product sold without a required warning can count as a separate violation.10State of California – Department of Justice – Office of the Attorney General. Frequently Asked Questions – View All Settlements typically include attorney’s fees and costs on top of penalties, and the fees often exceed the penalty. Based on data reported to the Attorney General’s office, the average settlement for private enforcement actions has historically hovered around $42,000, though amounts vary widely with the chemical, product volume, and duration of the alleged violation.11State of California – Department of Justice – Office of the Attorney General. Proposition 65 Enforcement Reporting
That is the practical reason the safe harbor analysis matters. A defensible file showing the lab results, the exposure model, and the comparison to the applicable NSRL or MADL is what stops a 60-day notice from turning into a settlement demand.