The #1 reason irritation testing gets rejected? You’re using the wrong exposure route.

We’ve reviewed dozens of irritation studies that looked solid—until they reached regulators. The science was technically sound, but the contact model didn’t match the real-world use of the device. That mismatch? It’s an automatic red flag for the FDA and EU reviewers.

Let’s break down why it happens and how to avoid the delay.
Route of Exposure = Contact Type
Here’s the bottom line:

Skin is not the same as mucosa. Mucosa is not the same as ocular. Ocular is not the same as nasal.

Each type of tissue has different sensitivities, absorption characteristics, and regulatory expectations. That means each requires a tailored irritation model. One-size-fits-all doesn’t work in toxicology.

A Common (and Costly) Mistake
Real-World Example:

A client submitted irritation data for a vaginal-use device. They had used a dermal irritation model—because that’s what was familiar and available. The results? The study technically passed… but the FDA flagged it as not clinically relevant.

The outcome?

5-month delay
$$$$ in additional testing
Resubmission required

When we reran the study using the correct mucosal model, it passed again—and this time, it got accepted.

How to Get It Right
Let’s say you’re developing:

A topical vaginal cream → You’ll need a mucosal irritation model—not rabbit skin.
An eye drop or ocular device → Dermal testing is irrelevant. Use ocular-specific irritation testing.
A nasal spray or swab → Think respiratory mucosa, not general skin contact.
The key is to simulate how and where the patient will use your product. That’s what regulators are looking for.

Toxicologist Pro Tip
Before choosing your test model, map your device’s contact type to the exposure route. Is it surface? Mucosal? Ocular? Implant?

Then design your irritation testing to reflect real-world conditions. The closer your model simulates patient exposure, the stronger—and more acceptable—your data will be.

Bottom Line
If your exposure route isn’t accurate, your irritation data won’t stand up.

Design smarter. Justify early. Avoid rework.

Let’s Talk
What’s the most confusing part of irritation study design for your team?

Contact us. We’ve helped dozens of MedTech innovators navigate this exact issue.
info@kandih.com
240.565.8933
www.kandih.com

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