Skincare products company Rodan + Fields is facing a second federal class action lawsuit alleging that the multi-level marketing company failed to disclose the harmful side effects of a key ingredient in its Lash Boost eye serum which it claims gives users "the appearance of lush, longer-looking lashes."

As in an April 13 lawsuit, the new case singles out isopropyl cloprostenate, a type of medication called a prostaglandin analog that's used to treat glaucoma and other eye diseases. It has been linked to dry eye, eye irritation, eye inflammation, eye redness, and macular edema, the latest lawsuit says, and had the lead plaintiff, Melissa Ryan of San Diego, known about the "documented health risks" of the chemical, she wouldn't have purchased Lash Boost or would have paid less for it.

"R+F (Rodan + Fields) further claims that for 'best results,' use Lash Boost daily for 8 weeks, which would likely require a customer to buy at least two tubes of the costly (retail price of about $150) Lash Boost and further exposing the consumer to potential serious health effects," according to the court filing.

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Attorneys for Ryan and a spokesperson for Rodan + Fields couldn't immediately be reached for comment. San Francisco-based Rodan + Fields has disputed the claims in the earlier case.

Rodan + Fields also is in a legal tussle with skincare rival Procter & Gamble's Olay Regenerist line over the marketing of serums that promise to reduce the appearance of wrinkles.

The dispute centers around the different Vitamin A derivatives used in the companies' products. Rodan+Fields' Intensive Renewing Serum contains retinal, which is a precursor to prescription drugs called retinoids used to treat skin conditions such as acne and psoriasis. Procter's Olay Regenerist line uses Pro-Retinol, a Vitamin A formulation patented by the company.

Rodan + Fields claims the retinal in its product has 20 times the strength of Procter & Gamble's Retinol and is the closest to prescription strength Vitamin A that's available on the market. It's a claim that Procter & Gamble disputes.

Procter & Gamble sent Rodan + Fields a cease and desist letter in December 2017 over what Procter considered to be "false and misleading" claims on Rodan's website, YouTube videos and on social media posts made by Rodan's independent consultants about the efficacy of retinal and the Intensive Renewing Serum.

Two months later, Procter & Gamble filed a complaint against Rodan + Fields with the National Advertising Division (NAD) of the Better Business Bureau. Cincinnati-based Procter requested that the NAD order Rodan + Fields to quit making the misleading claims or risk a referral to the Federal Trade Commission.

The NAD is the advertising industry's self-regulatory body tasked with examining complaints about advertising claims. Though its recommendations aren't binding, they often are followed. According to P&G, its complaint against Rodan + Fields has been put on hold temporarily.

"Olay questioned the accuracy and truthfulness of Rodan + Fields advertising of its Intensive Renewing Serum and, in line with industry standards, filed a complaint with the NAD," Kate DiCarlo, a spokeswoman for Olay, wrote in an email. "We are disappointed that Rodan + Fields refused to participate in the self-regulatory process and instead sought protection in federal court."

DiCarlo is referring to a federal lawsuit filed in March by Rodan + Fields that alleges Procter & Gamble is illegally trying to block the marketing of Rodan + Fields' Intensive Renewing Serum so that the consumer products giant can gain an edge for its rival Olay Regenerist line.

"P&G does not want consumers to know about the ingredients in Rodan + Fields' Intensive Renewing Serum or the product's attributes and is actively trying to limit Rodan + Fields' ability to truthfully advertise them," according to a March 23 court filing.

Rodan + Field has vowed to fight what it sees as a "baseless legal challenge" from P&G. "We stand by the quality of our products and the claims made in marketing our Intensive Renewing Serum," according to a Rodan + Fields statement.

There is plenty at stake for both companies. Rodan + Fields generated $1.5 billion in beauty product retail sales including skin care in 2017, topping Olay, which had $932 million, according to Euromonitor.

Dr. Anthony Rossi, a dermatologist at Memorial Sloan Kettering Cancer Center in New York, urges consumers to be skeptical about claims made by makers of anti-aging products. "Marketing claims can be based on a variety of data that usually is not published and therefore not subject to scrutiny," he wrote in an email.