What is Read-Across?
Read-across is a scientific method used to predict the safety profile of one chemical by comparing it to similar chemicals that have already been tested.
Instead of repeating animal studies, companies can use existing data – provided they can justify scientifically why the substances behave similarly.
Why is Read-Across Used?
- Reduces animal testing (3Rs principles)
- Saves time and cost
- Speeds up REACH registration
- Supports EFSA submissions
- Helps address data gaps in legacy portfolios
When Does Read-Across Work Well?
- Substances share clear structural similarity
- They follow the same metabolic pathways
- There is a consistent toxicological pattern
- High-quality data exist for source substances
When is Read-Across Risky?
- Structural similarity without mechanistic similarity
- Unknown metabolites
- Diverging physicochemical properties
- Poor study reliability
- Complex endpoints (e.g., developmental toxicity)
Read-Across is Powerful – But Not Automatic
Regulators expect structured scientific justification, not assumption.
When designed properly, read-across can:
✔ Reduce animal testing.
✔ Accelerate compliance.
✔ Withstand regulatory scrutiny.
When poorly constructed, it delays approvals and invites challenge.
Considering Read-Across for Your Substance or Product?
The right strategy can save time, reduce testing, and strengthen your regulatory position – but only if it’s built on solid scientific foundations from the start.
If you’d like to explore whether read-across is suitable for your portfolio, our team of regulatory compliance consultants would be delighted to talk it through with you.
