Under California’s Proposition 65, the Maximum Allowable Dose Level is a numeric safe harbor for reproductive toxicants: a daily exposure ceiling, expressed in micrograms per day, below which a business does not have to place a warning on its product. If you can show that a consumer’s daily exposure to a listed chemical stays at or under the published MADL, the warning requirement in Health and Safety Code Section 25249.6 does not apply, and the product is shielded from state and private enforcement actions built on a failure-to-warn theory.1Office of Environmental Health Hazard Assessment. Proposition 65 No Significant Risk Levels (NSRLs) and Maximum Allowable Dose Levels (MADLs)
What the MADL Does
Proposition 65 bars businesses from knowingly exposing anyone in California to a listed chemical without a clear and reasonable warning first.2California Legislative Information. California Health and Safety Code 25249.6 Read literally, that sweeps in nearly any product carrying a trace of a listed substance. The MADL is what makes the rule workable. It converts an open-ended legal risk into a specific number a laboratory can measure against.
One boundary matters up front: MADLs apply only to chemicals listed as reproductive toxicants. Chemicals listed as carcinogens are governed by a separate safe harbor, the No Significant Risk Level (NSRL), which is calculated differently. Some chemicals sit on both lists. Benzene is one. A product involving a dual-listed chemical must clear both thresholds independently to avoid a warning entirely.1Office of Environmental Health Hazard Assessment. Proposition 65 No Significant Risk Levels (NSRLs) and Maximum Allowable Dose Levels (MADLs)
How the Number Is Set
Regulators start with the No Observable Effect Level (NOEL): the highest exposure in the most sensitive high-quality study at which no reproductive harm was seen, measured in milligrams per kilogram of body weight per day.3Legal Information Institute. California Code of Regulations Title 27 Section 25803 – Assessment When more than one reproductive effect drove the listing, the lowest resulting NOEL controls.
The NOEL is then divided by 1,000 to produce the MADL.4Legal Information Institute. California Code of Regulations Title 27 Section 25801 – General That factor of a thousand is a built-in cushion for differences between test animals and humans, differences in sensitivity across the population, and gaps in the underlying data. The published MADL sits well below any dose where harm was actually observed.
Route of Exposure Changes the Number
A single chemical can carry more than one MADL. The route matters. Lead has an oral MADL of 0.5 micrograms per day. Benzene is set at 24 micrograms per day for ingestion and 49 micrograms per day for inhalation. Bisphenol A has a 3-microgram-per-day MADL specifically for dermal contact with solid materials.5Legal Information Institute. California Code of Regulations Title 27 Section 25805 – Specific Regulatory Levels All MADLs are stated in micrograms per day, and the range across chemicals is wide: methanol’s oral MADL is 23,000 micrograms per day.
When a product delivers exposure through more than one route at once, the exposures are combined using an additive formula. For benzene, the safe harbor is lost when the oral dose divided by 24 plus the inhalation dose divided by 49 exceeds 1.0.1Office of Environmental Health Hazard Assessment. Proposition 65 No Significant Risk Levels (NSRLs) and Maximum Allowable Dose Levels (MADLs) Missing a secondary route is a common way to fail the analysis while thinking you have passed it.
The full table of established MADLs sits in Title 27 of the California Code of Regulations, Section 25805, and OEHHA maintains a downloadable version on its website.5Legal Information Institute. California Code of Regulations Title 27 Section 25805 – Specific Regulatory Levels
Running the Compliance Calculation
Compliance comes down to comparing two numbers: how much of the listed chemical a consumer takes in from your product per day, and the MADL for that chemical and route.
First, pull the correct MADL from OEHHA’s current list, and pull it for the right route. Second, get laboratory results on the concentration of the chemical in your product, typically reported in parts per million or micrograms per gram. Third, estimate the amount of product a consumer uses or consumes in one day. Multiply concentration by daily use to get daily exposure. If a product contains 0.5 micrograms of a chemical per gram and a typical consumer uses 2 grams per day, daily exposure is 1.0 microgram, which you then compare directly against the MADL.
If exposure exceeds the MADL by any margin, the safe harbor disappears and the product needs a warning. Keep every piece of paper this analysis generates. Lab reports, usage assumptions, calculation worksheets, and the version of the MADL table you relied on are what a business actually uses to defend a safe harbor claim later.
When No MADL Has Been Published
OEHHA has listed hundreds of reproductive toxicants but has adopted formal MADLs for only a portion of them. The warning requirement still applies to the rest. No published number does not mean no obligation; it means the analytical burden falls entirely on the business.
The most common route is a private risk assessment. A qualified toxicologist reviews the available literature, identifies a defensible NOEL from studies of the reproductive effect that drove the listing, and applies the same thousandfold safety factor the state uses.3Legal Information Institute. California Code of Regulations Title 27 Section 25803 – Assessment The assessment has to follow generally accepted scientific methodology, and it has to be documented well enough to hold up in litigation, because in an enforcement action it is your primary evidence. OEHHA has acknowledged that businesses may use alternative safe harbor levels if they can show scientific validity.1Office of Environmental Health Hazard Assessment. Proposition 65 No Significant Risk Levels (NSRLs) and Maximum Allowable Dose Levels (MADLs)
The other route is a Safe Use Determination from OEHHA itself. The request carries a $1,000 non-refundable processing fee and requires detailed product information, supporting data and studies, and a statement that the product is not already the subject of a Prop 65 lawsuit or 60-day notice. Companies pay for OEHHA’s evaluation costs, including staff time, as the review proceeds. OEHHA encourages informal consultation before filing, reachable through Proposition 65 Implementation staff at 916-445-6900.6Office of Environmental Health Hazard Assessment. Proposition 65 Safe Use Determination (SUD) Process For most small and midsize businesses, a private assessment is faster and cheaper.
Grace Period for Newly Listed Chemicals
When OEHHA adds a chemical to the Prop 65 list, the warning obligation for that chemical does not begin immediately. It takes effect one year after the listing date.7Office of Environmental Health Hazard Assessment. Frequently Asked Questions for Businesses – Proposition 65 Warnings That window is designed to give companies time to test, calculate exposure, and either reformulate or prepare labels. It closes quickly in practice, especially when lab queues are long or a supplier change is involved.
If Exposure Exceeds the MADL
Once daily exposure runs above the MADL, the product needs a clear and reasonable warning delivered before exposure occurs.2California Legislative Information. California Health and Safety Code 25249.6 For physical goods, that generally means a label on the packaging. For brick-and-mortar retail, a prominent point-of-sale sign works. For online sales, the warning must appear before the buyer completes the transaction.
The warning uses the yellow triangle symbol with a black exclamation point (black and white is acceptable when the label is not printed in color), the signal word “WARNING,” and text in no smaller than 6-point font.8Proposition 65 Warnings. Warning Symbol For products manufactured on or after January 1, 2028, the short-form warning has to name at least one listed chemical for each health endpoint covered. Products manufactured and labeled before that date can continue to use the older short-form language.7Office of Environmental Health Hazard Assessment. Frequently Asked Questions for Businesses – Proposition 65 Warnings
Who Has to Comply
Prop 65 applies to businesses with 10 or more employees that operate in California or sell into the state. Businesses under 10 employees, and government agencies, are exempt from both the warning requirement and the discharge prohibition.9Office of Environmental Health Hazard Assessment. Businesses and Proposition 65 The employee count is easy to miscount. Contract workers, part-time staff, and employees of affiliated entities can push a company across the line, and selling to California consumers online counts as operating in the state even without any physical presence there.
Enforcement Risk Without a Documented MADL Analysis
Prop 65 is enforced not only by public agencies but by any private individual acting in the public interest. Before filing suit, the private enforcer must serve a 60-day notice on the California Attorney General, the relevant local prosecutor, and the business, and a failure-to-warn notice under Section 25249.6 has to include a certificate of merit.10California Legislative Information. California Health and Safety Code 25249.7 Civil penalties reach $2,500 per day per violation.11Proposition 65 Warnings. What Are the Penalties for Violating Proposition 65 Most cases settle, often for five- or six-figure amounts that also cover attorney fees and sometimes require reformulation or new labels.
The businesses that resolve these notices quickly, or defeat them outright, are the ones that already have the exposure calculation on file with the lab data behind it. The businesses that never ran the numbers tend to settle, because without a documented MADL analysis they have no way to prove the safe harbor applied.