Senior cats: ‘forever chemicals’ in the blood weren’t tied to hormone disease

If you share your home with one of the senior cats now dozing in a sunny window, here is some good news. Researchers found “forever chemicals” in the blood of nearly every cat and dog they tested. But once they accounted for age, those chemicals were not linked to hormone diseases, including the overactive thyroid that is so common in older cats.

That means finding PFAS in your pet’s blood is not a sign that your pet will get sick. It mostly tells us these chemicals are everywhere, in homes, in food packaging and in the dust on the floor.

How the study worked

Veterinary researchers in Italy and the Netherlands tested blood from 84 cats and 179 dogs. The samples were collected between 2021 and 2025 at the Universities of Bologna and Utrecht. Some animals were healthy, and others had hormone conditions such as hyperthyroidism in cats, or Cushing’s disease and adrenal tumors in dogs. The team looked back at these records and compared groups, and it published the work on Aug. 24, 2026, in Frontiers in Veterinary Science. Because nearly every animal had some PFAS, there was no truly unexposed group to compare with, and longer studies that follow pets over time will add to the picture.

What they found

PFAS are man-made chemicals used in non-stick pans, stain-resistant fabrics and food packaging. They break down very slowly, which is why people call them forever chemicals.

The most common one, PFOS, showed up in 99.0% of the cats and 99.5% of the dogs. Another, PFOA, turned up in 96.0% of the cats and 68.5% of the dogs. Dogs from the Dutch university had higher PFOS levels than dogs from the Italian one.

At first glance, the numbers did show some differences between healthy and sick animals. But they went in opposite directions. Healthy cats had higher PFAS levels, while some groups of sick dogs did. That mixed picture was a clue.

The key was age. Sick animals were older than healthy ones. And in both dogs and cats, PFAS levels were a little lower in older animals (a weak link, with a correlation of -0.234 in cats and -0.206 in dogs). Once the researchers adjusted for age, no PFAS was tied to any hormone disease in either species. Body condition score, a check of whether a pet is lean or heavy, showed no link either.

In plain words: age explained most of the differences, not the chemicals.

Why age matters in a study like this

Older pets are more likely to get hormone diseases. If a study doesn’t account for that, it can blame a chemical for something that is really about getting older. Adjusting for age is how scientists separate the two. Here, that step cleared the PFAS of any link to these conditions.

What you can do today

Pick up your phone and start a short note about your senior cat. Jot down anything you notice about thirst, appetite or weight, with today’s date. Bring it to your next vet visit. Those simple clues help your vet spot common older-cat conditions, like an overactive thyroid, early.