A spokesperson for the company told BuzzFeed News it "stand[s] behind the safety and efficacy of lash boost."

A group of unhappy Rodan + Fields customers have filed a class-action lawsuit against the company, saying its "lash boost" serum left them with swollen, red, and crusty eyes.

Rodan + Fields is a skin care brand sold through multilevel marketing. In 2016, it launched its $150 Lash Boost serum, which promises customers the appearance of longer and fuller eyelashes in as little as four weeks.

The company itself touts the product as an "eyelash-conditioning" serum.

Independent sellers of Rodan + Fields, known as consultants, frequently market the product as safe and full of biotin, a vitamin, and keratin, a protein.

"You curl them, paint them, glue things to them, even try fake ones...but have you ever just given them vitamins?" one consultant wrote on Facebook in January. "That’s exactly what RF Lash Boost does."

While Lash Boost does contain biotin and keratin, one of its other ingredients has been well known to the FDA and eye doctors for years: isopropyl cloprostenate.

Isopropyl cloprostenate is a synthetic type of compound known as a prostaglandin analog, which is required to be labeled as a drug by the FDA.

These types of drugs were originally used to help glaucoma patients and came into popular use for eyelashes after doctors realized that they inadvertently led to eyelash growth.

However, these drugs can also cause side effects, like eye irritation, red eyes, blurred vision, inflammation, lid crusting, swelling around the eyes, and cysts, according to the FDA.

Because the ingredient “affects the structure and function of the body” — they cause eyelashes to grow and can lower the pressure inside the eye, among other things — the FDA requires products containing these compounds to be labeled as a drug.

There is one FDA-approved eyelash growth product, Latisse, and you need a prescription to get it.

However, companies have been dinged in the past for trying to circumvent the FDA, by labeling their products as a “cosmetic,” but then making claims — like eyelash growth — that clearly make them sound like drugs.

In 2011, the FDA warned the manufacturer of eyelash-growth products like RapidLash, NeuLash, and NeuveauBrow for doing exactly that.

The FDA said in a warning letter that the products were "not safe for use except under the supervision of a practitioner licensed by law to administer them."

Prostaglandin analogs are also known to be potentially harmful to pregnant women, according to the FDA.

Eye doctors have also warned about the potentially harmful effects of isopropyl cloprostenate, and have criticized cosmetic companies for not warning customers of the potential risks.

Optometrist Dr. Jennifer Lyerly, of Triangle Visions Optometry, said in a 2017 blog post that Rodan + Fields claims Lash Boost contains "no active medical ingredient," but has the same side effects as any other drug containing prostaglandin analogs.

She wrote this "makes it all the more confusing for potential patients trying to do their due diligence if they know they have a previous diagnosis of dry eye or are at increased risk."

"There is a major push within the medical community to have the FDA put stronger regulations on beauty products that are using chemicals with known side effects without disclosing the risks involved, but regulation and oversight may be many years away," she wrote.