While oats do not actually contain gluten, almost all oats are grown in close proximity to wheat, rye, and/or barley. And they are processed in facilities that also process wheat, rye, and/or barley, as well as transported in trucks that have carried wheat, rye, and/or barley. So they are usually contaminated.
But, it is now possible to buy gluten-free oats. These oats are grown and processed completely separate from wheat, rye, and/or barley. And they have been tested to make sure they meet the gluten-free standards of under 20ppm.
Plus, there is a small percentage of people with celiac disease who have an adverse reaction to the protein in oats. So, it is best to consult with your doctor if you are going to add gluten-free oats to your diet. Your doctor will probably want to test you to make sure you are tolerating them.