On Tuesday, the agency responsible for policing the American food and drug market issued warning letters to 14 companies that it says are "illegally selling more than 65 products that fraudulently claim to prevent, diagnose, treat or cure cancer."

"There's a couple of issues here," Jason Humbert, a regulatory operations officer in the FDA's Office of Regulatory Affairs, told CNN. "The FDA's role is to review and evaluate products for safety and effectiveness, particularly products that are intended for the treatment of a disease like cancer. Cancer requires the supervision of a licensed health care provider."

The companies that received the warning letters are required by law to respond in a timely fashion, indicating whether they intend to pull the products under scrutiny from the market or alter the advertising and packaging to comply with the agency's rules and regulations.

"Failure to correct the violations promptly may result in legal action, including product seizure, injunction and/or criminal prosecution," the FDA said in a statement.

What products were targeted?

Products included in this crackdown include pills, creams, ointments, oils, drops, syrups and teas. The FDA says they are most commonly marketed and sold online, especially on social media platforms such as Facebook and Instagram.

The companies that received warning letters from the FDA are AIE Pharmaceuticals, Inc.; Amazing Sour Sop Inc.; BioStar Technology International LLC; Caudill Seed & Warehouse Inc.; DoctorVicks.com; Everything Herbs; Hawk Dok Natural Salve LLC; Healing Within Products & Services Inc.; LifeVantage Corp.; Nature's Treasure Inc.; Oxygen Health Systems LLC; Sunstone Inc.; The Vibrant Health Store LLC dba Dr. Christopher's Herbs; and The Vitamin C Foundation. The entire list of product names (as well as the letters that were sent to each of the companies) can be found on the FDA's website

Amazing Sour Sop said it is working to address the issues. DoctorVicks.com said it is updating product descriptions. In its statement to the FDA, AIE Pharmaceuticals, Inc. enumerated all the changes and deletions to its website and added that its Facebook pages "have been deleted which include all products." Darren Jensen, CEO of LifeVantage replied that "We will respond to the FDA in a timely fashion and make any changes needed to further ensure our compliance."

Hawk Dok Natural Salve said it is changing its labels and maintains that it "has found the natural way to fight off cancer and the HPV virus."

A statement from The Vitamin C Foundation founder Owen Fonorow read, in part, "This is not the first time the FDA has attacked vitamin C trying to create the impression that vitamin C is an illegal drug. In my opinion, these attacks by the Government on vitamin C have little or nothing to do with the public interest or public health."

Nature's Treasure declined to comment. The other companies have yet to respond to a request for comment.

"Consumers should not use these or similar unproven products because they may be unsafe and could prevent a person from seeking an appropriate and potentially life-saving cancer diagnosis or treatment," said Douglas W. Stearn, director of the FDA's Office of Enforcement and Import Operations, in a written statement. "We encourage people to remain vigilant whether online or in a store, and avoid purchasing products marketed to treat cancer without any proof they will work. Patients should consult a health care professional about proper prevention, diagnosis and treatment of cancer."

Humbert said that beyond postponing vital treatment, some of the products targeted in this crackdown contain ingredients that themselves could cause consumer harm. "There's also concern that some of the products could interact with any medications or any other underlying conditions that consumers may have."

What should consumers look out for?

"I think the biggest red flag would be that any product that hasn't undergone FDA review is making a claim that it can treat or cure cancer," Humbert said. "Only products that have been evaluated -- approved FDA drugs -- can make those claims. So if a consumer happens upon a website or a social media site and they see that this product is marketed as a natural cure for cancer or a natural treatment for cancer, they should be very skeptical, because unless that product has been evaluated by FDA, there's no reason to believe it's safe or effective for that use."

Although claims vary from product to product, the FDA says fraudulent cancer products "often use a particular vocabulary." The agency identified these phrases as the most common red flags

Treats all forms of cancer

Miraculously kills cancer cells and tumors

Shrinks malignant tumors

Selectively kills cancer cells

More effective than chemotherapy

Attacks cancer cells, leaving healthy cells intact

Cures cancer

"The overarching point is that these products are untested, and some of the ingredients may present direct risk to the consumer's health or interact with any medications they might be taking," Humbert said. "They're not a substitute for appropriate treatment, and using these products can not only endanger consumers' health but waste their money and waste their time, as well."

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Nicole Kornspan, a consumer safety officer at the FDA, said in a written statement that "Anyone who suffers from cancer, or knows someone who does, understands the fear and desperation that can set in. There can be a great temptation to jump at anything that appears to offer a chance for a cure."

Just remember the old saying: If something seems too good to be true, it probably is.