Bryan Vander Dussen spent years as a dairy farmer before shifting to selling farm-raised beef. In the past year, he and his wife have been making another transition: Cooking up recipes in their kitchen that turn organ fat from his animals into tallow balm that buyers are eager to slather on their skin.

One tricky bit: Coming up with formulas that don’t smell like pot roast.

“You see it everywhere, so we were like, ‘Why don’t we do this?'” he said. “Some of the feedback is, ‘We don’t want to smell like beef,’ so we add things like lavender and wild orange to kind of counter that potential beef smell.”

From moisturizers made with beef tallow to salmon sperm facials, consumers have become more interested in animal-based skin care products in recent years. Promoted as natural alternatives to synthetics, they’re gaining popularity across social media and high-end spas as well as at farmers’ markets and in home kitchens.

Some experts connect the products’ rise to an increased focus on the health impact of chemicals, as well as pro-meat messaging from the Make America Healthy Again movement.

“There’s been a movement in the last couple of years to embrace animal-based foods,” said Norah MacKendrick, an associate professor of sociology at Rutgers University who has studied why consumers are worried about chemicals in their personal care products.

Here’s what experts have to say about animal-based skin care, including cautions about a lack of medical evidence for their effectiveness.

The cosmetics industry moved away from many animal-derived ingredients decades ago amid concerns about animal testing and disease outbreaks like mad cow, said Perry Romanowski, an independent cosmetic chemist who studies how skin care ingredients are formulated.

For years, those concerns, along with the rise of vegan beauty products, pushed many brands to avoid animal-based ingredients altogether. But recently, some of those materials have started to reappear in skin care products and are often marketed as natural alternatives.

Vander Dussen, the California rancher, said he and his wife are “just kind of jumping onto the fad that’s already there.” He added: “In today’s world, it’s very important not only what you are putting on your face but where it comes from.”

Kelly Pratt, who owns a spa in Tampa, Florida, said demand for treatments like salmon sperm DNA facials have surged because clients report improvements over time. Cassandra Hutchison, an aesthetician who gives the treatments at the spa, said the ingredient is intended to repair skin and keep inflammation down. She said it helps in hydration, making skin look healthier and repairing damage to the outer layer of skin that keeps moisture in and irritants out.

Prices vary, but a tub of tallow balm at Target costs about $15 more than a tub of petroleum jelly. And while there are some salmon sperm products like masks you can apply at home, many have to be applied at a spa, which comes with its own costs. Still, that hasn’t deterred some consumers, whose searches for terms like “beef tallow for skin” have jumped in recent years and remained higher than ever before, according to Google Trends.

Turning waste from an animal product into something people use is certainly an example of sustainability, experts said.

But neither beef tallow nor salmon sperm have robust medical data to support their effectiveness, said Dr. Angelo Landriscina, a New York City dermatologist who has taken to social media to debunk what he sees as skin care misinformation.