“Natural treats/chews can contain chemicals from processing or bacterial contamination. This can be harmful to the pet, and even the owner,” Tanner says. “Some pets may chew appropriately, but others may chew off and swallow large pieces that can lead to stomach upset, or worse intestinal blockages.” In addition, pets can sometimes be allergic to the animal proteins. Some treats are high in calories which—if you feed them too frequently—can lead to obesity issues.