Understanding NSRL vs MADL: The Foundation of Prop 65 Compliance (2026)

Introduction: Why NSRL and MADL Matter in Prop 65 Compliance

If you are evaluating California Proposition 65 compliance, two regulatory thresholds determine whether your product requires a warning:

NSRL (No Significant Risk Level) and MADL (Maximum Allowable Dose Level).

These are not just technical definitions—they are the core decision points that determine compliance outcomes. Your entire Prop 65 strategy depends on how your product’s exposure compares to these limits.

What Is NSRL (No Significant Risk Level)?

NSRL applies to chemicals that cause cancer. It represents the exposure level at which no more than one additional cancer case would occur per 100,000 individuals over a lifetime.

Key Characteristics of NSRL

Applies to carcinogenic chemicals
Based on lifetime exposure risk
Expressed in micrograms per day (µg/day)
Established by the California Office of Environmental Health Hazard Assessment (OEHHA)

Compliance Interpretation:

Exposure ≤ NSRL → No warning required (with documentation)
Exposure > NSRL → Warning required

What Is MADL (Maximum Allowable Dose Level)?

MADL applies to chemicals that cause reproductive toxicity, including birth defects or developmental harm. It represents a level of exposure that is significantly below levels known to cause harm.

Key Characteristics of MADL

Applies to reproductive toxins
Includes a built-in safety factor (typically 1,000x)
Expressed in micrograms per day (µg/day)
Also established by OEHHA

Compliance Interpretation:

Exposure ≤ MADL → No warning required (with documentation)
Exposure > MADL → Warning required

NSRL vs MADL: Key Differences

NSRL: Based on lifetime cancer risk
MADL: Based on reproductive toxicity thresholds
NSRL: Statistical risk model
MADL: Built-in safety margin approach

Both thresholds serve the same purpose: determining whether a Prop 65 warning is required.

How NSRL and MADL Are Applied in Prop 65 Compliance

To apply these thresholds, businesses must perform an exposure assessment.

Step-by-Step Process

Identify the chemical present in the product
Measure concentration through laboratory testing
Calculate daily exposure based on usage or consumption
Compare calculated exposure against NSRL or MADL

Decision Logic:

Exposure exceeds NSRL or MADL → Warning required
Exposure is below threshold → No warning required (documentation required)

This calculation is the foundation of Prop 65 compliance.

Real-World Example: Lead Exposure

Lead is commonly regulated under Prop 65 for reproductive toxicity. The MADL for lead is extremely low, meaning even trace exposure levels may trigger warning requirements.

Two products with similar lead content may have different compliance outcomes depending on daily exposure levels.

Why NSRL and MADL Are Critical

A common misconception is that the presence of a chemical automatically requires a warning.

This is incorrect.

Compliance is determined by exposure—not presence. The same chemical may require a warning in one product and not in another depending on exposure levels.

Common Mistakes in Applying NSRL and MADL

Skipping exposure assessment entirely
Using incorrect serving size assumptions
Relying only on concentration data
Misinterpreting NSRL vs MADL applicability
Failing to document calculations

Enforcement actions often focus on whether your exposure calculations are accurate and defensible.

Required Documentation for NSRL and MADL Compliance

Laboratory testing reports
Exposure assessment calculations
NSRL and MADL reference data
Assumptions and methodology documentation
Compliance determination records

Documentation is required whether a warning is issued or not.

Why NSRL and MADL Form the Foundation of Prop 65

Every compliance decision under Prop 65 comes back to one question:

Does exposure exceed NSRL or MADL?

Warning requirements depend on it
Compliance strategy depends on it
Legal defensibility depends on it

Without understanding these thresholds, compliance becomes unreliable and difficult to defend.

Frequently Asked Questions (FAQ)

What is the difference between NSRL and MADL?

NSRL applies to cancer risk, while MADL applies to reproductive toxicity. Both are exposure thresholds used to determine warning requirements.

Do all chemicals have NSRL or MADL levels?

No. Not all listed chemicals have established safe harbor levels, which may require additional risk assessment.

Is a warning required if a chemical is present?

No. A warning is required only if exposure exceeds NSRL or MADL thresholds.

Who establishes NSRL and MADL values?

These values are established by the California Office of Environmental Health Hazard Assessment (OEHHA).

Final Thoughts: Compliance Starts with Exposure

NSRL and MADL are the foundation of decision-making under Proposition 65. Effective compliance requires accurate exposure calculations, proper testing, and structured documentation.

Get Expert Support for Exposure Assessment

If you are unsure how to calculate exposure or apply NSRL and MADL correctly, a structured compliance approach is essential to ensure accuracy and defensibility.

In Prop 65 compliance, one principle applies:

It is not just what is in your product—it is the level of exposure it creates.