A small amount of people with celiac disease have an adverse reaction to oats but the problem is in another protein present in oats, called avenin.
Avenin contains amino acid sequences similar to that of wheat gluten.
That explains why some people with celiac disease have no problem with oats while others do.
It is estimated however that only 1% of celiacs react to a large amount of oats due to avenin.
Another problem with oats is that the grain is often produced and packaged by the same manufacturers who deal with wheat, rye or barley.
That means that ‘contamination’ of oats with the grains with gluten is very possible even likely, making oats dangerous for people with celiac.
To be on the sure side, dietitians recommend that people with celiac disease should remove oats from their diet when they start the gluten-free regime, to give their intestinal lining time to recover. It might take about year or so. (1, 2)
There are many companies these days that offer uncontaminated, gluten-free oats.