Advice What are Hairballs? Hairballs are usually harmless unless your cat is coughing them up frequently. The hair may have hardened and caused a blockage of the intestinal tract, and this condition can be fatal for your furry friend. It is common for your cat to swallow hair during the grooming process. The hair is usually passed through the body and eliminated, but there are times when the hair cannot make it through the intestinal tract. Your cat will vomit up what is known as a hairball, or trichobezoar.