The shift towards clean beauty is more than skin-deep.

These days in the makeup, hair and skincare space, nothing is buzzier than the term clean. Whether you're buying a mascara, moisturizer or hair mask, major retailers such as Sephora, Neiman Marcus and Target now offer an entire section dedicated to "cleaner" products. And studies show that the desire to have clean beauty is growing more than ever.

Market research company Statista reported that 76 percent of Gen Z consumers and 71 percent of millennials sought out clean beauty products in 2021 and 2022. And, yet, while it's clear that people are craving this change, the clean beauty wave is not without its blemishes.

To get the scope of the clean beauty industry, we called in the experts: Board-certified plastic surgeon Dr. Michele Koo—who also has experience formulating beauty products—and Dr. Christopher Spaeth, a Ph.D. Forensic Toxicology Consultant.

They answered our burning questions about clean beauty, so you can put your best face forward.

What is clean beauty?

In short, there isn't a standard definition. But Dr. Koo tells E! News there's a rule of thumb that many companies follow.

"It is generally accepted that clean implies the avoidance of ingredients that can harm humans," she said, "and some that are ecologically toxic." (As in, certain chemicals are thought to do harm to the environment. More on that, later.)

Why is there a spectrum of clean beauty?

The main reason there are so many meanings is that clean beauty is not a regulated term.

"The definition of 'clean' would be set by the company itself as part of branding and marketing," Dr. Spaeth, who previously worked as a cosmetics toxicologist, shared with E!. "The variations or spectrum of clean beauty are a result of limited regulations on cosmetics, as initially set forth in the 1976 Food, Drug and Cosmetic Act."

In other words, the FDA leaves it up to the brands to label and market their products. And while the FDA monitors the labeling of cosmetics, beauty products don't actually need to be approved by the government agency before hitting the market (with the exception of color additives; read the approved color additives here). So, again, it's up to the brands to do their due diligence. 

Another reason clean beauty has a wide-ranging definition is that a multitude of terms fall under its umbrella, including nontoxic, natural, organic, sustainable, green, vegan and cruelty-free. Many of those buzzwords are just as hard to pinpoint as well, with the exception of vegan—which doesn't contain any animal by-products or ingredients sourced from animals—and cruelty-free, which means it hasn't been tested on animals.

However, it's important to note that a product can be vegan and not cruelty-free—and vice versa.

What ingredients are typically not found in clean beauty?

According to Dr. Koo, many clean beauty brands avoid what's called the "dirty dozen." Generally speaking, you won't see the below list of ingredients on the back of a "clean" product label.

Phthalates: This is a group of chemicals used to make plastics more durable and flexible. They help dissolve other materials and are typically found in soaps, shampoos and hairsprays.

Butylated hydroxytoluene (BHT): This is a stabilizer that acts as an antioxidant to help maintain the properties and performance of cosmetics, especially when it's exposed to air.

Butylated hydroxyanisole (BHA): This is a preservative and antioxidant commonly found in lipsticks and moisturizers. It can also be used as a fragrance to mask the odors of a formula.

Parabens: These are a family of related chemicals—methylparaben, propylparaben, butylparaben and ethylparaben—commonly used as preservatives in cosmetics. In some cases, preservatives are described interchangeably with parabens.

Polyethylene glycols (PEGS): These are petroleum-based compounds and are mostly used as solvents or softeners for cream-based products. 

Fragrance: This can range from natural, synthetic and essential oil compounds found in cosmetics to either mask or create a pleasurable odor. It's important to note that under FDA regulations and the law, fragrance ingredients do not need to be specified on the label as to not "force a company to tell trade secrets."

Dye: Cosmetic dyes are considered color additives and requires FDA approval before being sold. Dyes are coloring agents found in various products, including eye makeup and nail polish.

Formaldehyde: This is typically used as a preservative to help fight against bacteria and other microbial growth in a product. It's commonly infused in nail polishes, hair gels, soaps, lotions, makeup and deodorants.

Triclosan: This is a chemical used for its antibacterial properties and is often found in soaps, cleansers, lotions and skincare creams.

Hydroquinone: This is a topical agent typically used to treat hyperpigmentation for its skin-bleaching effects. 

Benzophenone: This is a naturally occurring chemical found in plants and is mostly used as sunscreen in lotions, conditioners and other cosmetics. 

Sulfates: This is a group of surfactants, Sodium Lauryl Sulfate (SLS) and Sodium Laureth Sulfate (SLES), and create a foam or lather when infused into products. Both ingredients are commonly used in cleansing products, creams and lotions.

Ethanolamines: This ingredient comes from a group—Monoethanolamine (MEA), Diethanolamine (DEA), Triethanolamine (TEA)—and is also used as a surfactant and emulsifying agent. It's commonly found in cleansing products to help remove dirt and oil on the skin.

What ingredients have been given a bad reputation by clean beauty brands?

There are a couple of ingredients that have been put under a magnifying glass: Sodium Laureth Sulfates (SLES) and Parabens.

When it comes to SLES, one of the surfactants mentioned above, Dr. Koo explained that it's "inconsequential to the environment" if they're used in tiny amounts with cleansers for hair and skin. "The concentration after being diluted from face and hair washing is not harmful to our waterways," she said. "This ingredient has actually been thoroughly tested and approved for use by the FDA and the European Union. Sulfates in detergents and household cleaners are present in much greater quantities and can be toxic to fish and marine life. The two uses and concentrations are often confused."

Similarly, parabens, according to Dr. Spaeth, are another ingredient that has a bad reputation that "is not necessarily justified." 

While Dr. Spaeth noted that preservatives can cause irritation and allergies, he also pointed out that it depends on "the dose, the exposure, how often a person is exposed and whether or not that exposure to the preservative is bioavailable or is able to get into the body (as opposed to sitting on the outer layer of the skin)."

Overall, the purpose of preservatives is to prevent microbial growth—you know, bacteria, fungi and mold. "Exposing consumers to microbes that can grow in water-based products is an unnecessary hazard in most cases when preservation is available," Dr. Spaeth explained. "As a result of scientific and toxicological studies, the level of a preservative that can be used to kill microbes but not harm the user has been defined. Thus, the preservation process is based on scientific studies to specifically avoid harming the user as a result of contact with the preservative."

Dr. Spaeth said that parabens are continuously being tested and monitored, including by the FDA and Centers for Disease Control and Prevention. As he put it, "It could be argued that the most studied cosmetic ingredients are preservatives."

Is it better to have clean ingredients for beauty products?

As Dr. Koo explained, "Moisturizers and serums that stay on the skin all day and night need to contain safe ingredients and ingredient extraction processes that leave no trace toxins or solvents."

Of course, no one's asking you to go full college biology lab on your fave night cream. "It is impossible for the consumer to gain that information," she critiqued. "That is why it's really important to trust your brand and find the brand philosophy that resonates with you."

What should shoppers keep in mind when selecting clean beauty products?

No matter what you're buying—blush, lipstick, powder, eye cream, etc.—it's important to look at its shelf life. But unlike food products, which clearly mark items with a "sell by" or "best by" date, it's not quite as clear for beauty products. Many brands will place a sticker on the package that indicates the timeframe it will expire after opening it. The most common stamps are three months, six months and 12 months.

Generally speaking, you'll want to ditch mascara three months after it's opened, Jocelyn Biga, Estée Lauder's Director of Global Pro Artistry, previously told E! News. As for foundations and other water-based formulas, they should be replaced six to 12 months after breaking the seal, Allure reported. Powders, on the other hand, have a longer shelf life and can last for up to two years. But it's probably best to swap it out before then.

Technically, it's up to the brand and people who manufacture or market cosmetics to determine how long a product will last before it goes bad based on its testing, as the FDA doesn't require specific tests to demonstrate the safety of individual products or ingredients. The law also doesn't require companies to disclose their safety information to the FDA.

Another key factor to look out for when selecting products? Exactly what they're claiming to do. Is a retinol-based serum instructing the user to only apply it two to three times a week? Is there a disclaimer on a blush that warns against using it near the eyes? These messages, according to Dr. Spaeth, indicate "relevant toxicological information."

If you still want more information before selecting a beauty product, Dr. Koo advises reaching out to the company. 

"You should trust and believe the brand and the founder have tried some of its products," she said. "If you have questions and want to go one layer deeper, the company should answer any questions you could have honestly."

(This story was originally published on March 14, 2023 at 3:00 am PT.)