Hot dogs are everywhere in the United States. In fact, each summer, Americans consume almost 7 billion hot dogs, with a whopping 150 million consumed on the Fourth of July alone. According to a report from CBS, however, a recent study reveals that some pretty questionable ingredients go into all of those franks.

A report from Clear Foods described a method for using genomic technology to analyze the ingredients of hot dogs sold in the U.S., which opened the lid on a high number of things you wouldn’t want to eat intentionally.

The report scanned 345 different hot dog and sausage food products from 75 brands and 10 different distributors. Their results suggest that not all hot dogs are created equally, and there can be some unwanted ingredients in even the highest-end brands.

Hot dogs are typically processed in factories, using meat trimmings, spices, and a number of other ingredients that are diced, blended, and filled into giant stuffing machines. These machines pump emulsified meat into casings, which gives hot dogs their distinctive shape.

After being filled, the hot dogs are cooked inside of a smoke house, cooled under a water shower, and packaged for distribution. A common ingredient listed on the label of many hot dogs is “variety meats” – a term used to describe kidneys, livers, hearts, and other edible but less-than-desirable animal parts.

Variety meats are just the tip of the iceberg. The report from Clear Food found that 14.4 percent of the hot dogs sampled were problematic. The biggest problems facing hot dogs were ingredient substitutions and issues with hygiene. Substitution refers to ingredients being present in the product but absent from the label.

But perhaps the grossest thing the study found about hot dogs was that there was often human DNA present. Human DNA was found in 2 percent of the total sample, and in 2/3 of vegetarian hot dogs.

The study also found traces of chicken, beef, turkey, and lamb in food products that did not indicate their presence on the label. Pork was found in 3 percent of the hot dogs tested as well, which poses concerns for a number of groups who exclude pork from their diet for religious purposes. Pork substitution was by far the most common type of substituted meat found in hot dogs.

There were some other problems with the accuracy of hot dog labels relative to what the products actually contained. 10 percent of hot dogs labeled as vegetarian actually contained meat, including chicken and pork. Many hot dogs had labels that exaggerated the amount of protein in them by as much as 2.5 times.

Americans are typically concerned with what goes on top of their hot dogs, but the report suggests that it may be time to start paying attention to what’s inside of them too.