For nearly 6,000 years, essential oils have been used for cosmetic, spiritual and hygienic purposes. However, over the past few years, the growing industry has raised concerns from regulatory agencies and critics who say that companies are marketing essential oil products with unproven and unregulated medical claims.

A recent investigation into the marketing claims for essential oil by ATTN: found that companies and their distributors continue to promote essential oils for medical uses, such as helping fight breast cancer and melanoma, which goes against regulations.

This isn’t the first time the essential oils have been targeted over such claims. In 2014, the U.S. Food and Drug Administration (FDA) sent warning letters to some of the top essential oil companies, such as doTERRA and Young Living, over their marketing.

“Your consultants promote many of your Young Living Essential Oil Products for conditions such as, but not limited to, viral infections (including ebola), Parkinson’s disease, autism, diabetes, hypertension, cancer, insomnia, heart disease, post-traumatic stress disorder (PTSD), dementia, and multiple sclerosis, that are not amenable to self-diagnosis and treatment by individuals who are not medical practitioners,” the FDA said in its 2014 warning to Young Living.

DoTERRA, one of the top essential oil companies in the United States, was also warned at the time that the marketing for medical uses classified its products as drugs.

Media outlet ATTN: attained the response letter to the FDA from doTERRA through a public records request. In the response, doTERRA president David Stirling said the company had taken actions to conform with the agency’s request by reiterating its policies and hiring additional staff to ensure distributors adhered to guidelines.

Some Essential Oils Marketing Still Goes Against FDA Rules

Despite warnings from the FDA, a search of social media sites reveals distributors are continuing to promote essential oils for unregulated medical uses.

For example, in one Facebook post from November, an independent wellness advocate for doTERRA said diffused rosemary used topically and in cooking can help with cancer, hair loss, liver conditions, cellulite, depression and more. Other instances can be found on Twitter, Instagram and Pinterest.

According to the FDA, the agency does not approve essential oils before they make it to market, but it does regulate the labeling of the products.

“The law doesn’t require cosmetics to have FDA approval before they go on the market,” says the FDA website. “But FDA can take action against a cosmetic on the market if we have reliable information showing that it is unsafe when consumers use it according to directions on the label, or in the customary or expected way, or if it is not labeled properly.”

If an essential oil starts making medical claims, it becomes classified as a drug and would need to go through the agency’s drug-approval process.

According to Bill McGilvray, director of essential oil company Plant Extracts International, many companies have skirted federal regulations. He told ATTN: that besides a warning from the FDA, no visible action has been taken against violators.

He said bringing the topic to the attention of the appropriate authorities is one way of encouraging action.

Effectiveness of Essential Oils Not Proven in Humans

Despite thousands of years of use, little evidence exists about the safety and effectiveness of essential oils.

A few studies have noted possible benefits of essential oils. Several studies suggest that essential oils, particularly lavender, rose and frankincense, helped calm pregnant women during childbirth, according to University of Maryland Medical Center (UMMC). Peppermint oil was also found to relieve nausea and vomiting during delivery.

On the other side, a 2012 review of case studies published in a 2012 edition of the International Journal of Risk & Safety in Medicine found that essential oils led to a range of adverse effects, including one fatality. The most common side effect is a reaction, such as dermatitis, to essential oil creams.

“Although essential oils have been used for centuries, few studies have looked the safety and effectiveness of aromatherapy in people. Scientific evidence is lacking, and there are some concerns about the safety and quality of certain essential oils,” UMMC wrote. “More research is needed before aromatherapy becomes a widely accepted alternative remedy.”

In the end, since the FDA is unable to regulate the contents of essential oils, the agency encourages the public to remain wary of any scams promising cures that are too good to be true.

“Consumers should be mindful of health fraud scams, which are products that claim to prevent, treat or cure diseases or other health conditions, but are not safe and effective for those uses,” Lyndsay Meyer, a spokeswoman for the FDA, said to The Pueblo Chieftain. “Health fraud scams waste money and can lead to delays in getting proper diagnosis and treatment. They can also cause serious or even fatal injuries.”