Researchers call for stronger safety testing of lip cosmetics

New peer-reviewed publications find significant gaps in lip product regulation and safety testing, including reliance on inappropriate skin models and significant underestimation of usage and ingestion rates, leaving consumers exposed to potential risks.

Two international critical reviews into the testing and legal framework for lip cosmetic products have identified significant blind spots when it comes to ingestion rate data, tissue testing types, and ingredients used in products.

Lip cosmetics, including lipsticks, glosses, balms, oils, masks and stains, are classed as topical cosmetics for external use only. In practice, these products are routinely ingested and absorbed through lip tissue, resulting in a dual-pathway exposure route that existing frameworks were never designed to assess.

Commissioned by the Lip Service Alliance in partnership with University of Birmingham researchers, the studies have been published today in Integrated Environmental Assessment and Management.

The Lip Service Alliance is an independent non-profit working to modernise lip product safety standards and raise consumer awareness in this increasingly popular beauty category. The University of Birmingham is a founding member of the LSA, contributing expertise in environmental nanoscience, toxicology and legal regulation.

Researchers examined how absorption through lip tissue and incidental ingestion are assessed under cosmetics regulation in the UK, US, European Union, Canada, China and South Korea, and compared how the same exposure routes are treated differently across cosmetic, food and pharmaceutical frameworks.

The biological case for change

Most countries' testing and regulations do not account for absorption of lip cosmetic ingredients through skin. In stricter regions such as the UK, EU and China, absorption data is derived from regular skin models that have an intact barrier layer, which is biologically different to lip skin.

The lip vermilion has only three to five layers of protective cells, roughly one third the thickness of the equivalent layer on facial skin, has no oil glands or hair follicles, and blood vessels lying close to the surface, allowing a direct pathway into the bloodstream. This makes lip tissue behave more like oral mucosa, the lining of the mouth, than conventional skin.

Pharmaceutical science already exploits that route (oral mucosa) to deliver medicines rapidly into the bloodstream, bypassing the liver. The reviews cite studies showing substantially higher absorption through oral mucosal tissue than skin for compounds including benzoic acid, caffeine and hydrocortisone.

Despite this, no regulatory framework examined in the studies requires lip cosmetics to be tested on models reflecting these differences in skin tissue type.

In the United States, the 2022 Modernisation of Cosmetics Regulation Act (MoCRA) singled out products that regularly contact the mucous membrane of the eye for stricter oversight. It did not extend that recognition to products applied to the mouth.

Professor Iseult Lynch, Professor of Environmental Nanosciences at the University of Birmingham and a member of The Lip Service Alliance research team, said: "These critical reviews are an important first step in addressing a significant evidence gap in our understanding of how substances in lip products interact with the body. Through The Lip Service Alliance, we have brought together expertise from academia, industry and regulatory science to examine whether the assumptions used in current safety assessments accurately reflect the unique biology of the lips.

"Our findings suggest that the lips should not simply be treated as ordinary skin. They share important characteristics with the mucosal tissues inside the mouth, which are known to be considerably more permeable. This indicates a clear case for developing more lip-specific exposure assessment methods based on the best available science."

By identifying this knowledge gap, the researchers hope to encourage further studies and support for the development of testing approaches that give regulators, industry and consumers greater confidence in lip product safety.

Lacking or outdated ingestion assumptions

Every framework reviewed in the papers classifies lip products as cosmetic, which are assumed to stay on the outside of the body. Lip products therefore commonly use ingredients that are not assessed for chronic ingestion or absorption safety at modern-day usage rates.

While the EU and UK explicitly acknowledge some ingestion rates, the usage and exposure assumptions rest on studies that are over two decades old. The EU assessment assumes all of an applied lip product enters the body, using 0.057g a day at the 90th percentile for lipstick and lip salve. The US references 87mg a day at the 95th percentile for lipstick but has applied that ingestion figure for lead exposure only. Both derive from studies conducted between 2003 and 2005, and neither has been updated.

Canada, China and South Korea have never measured how much lip product their own populations use and rely on the European figures instead. That means safety in China, the world's second-largest cosmetics market, is assessed using a twenty-year-old survey of European consumers.

The lip cosmetics category has changed beyond recognition since those regulations were written, and several of the product types now driving growth (such as lip masks, lip oils, and long-wear lip stains) did not exist commercially at the time. Proprietary market research indicates 40% of US women aged 18 to 34 now use four or more different types of lip product, routinely applied in sequence, with social media encouraging more usage.

The publications point to contemporary studies documenting lip balm consumption of 1,270mg a day at the 95th percentile, 22 times the EU's current assumption of ingestion. At that rate, a heavy user of a single product accounts for roughly 463 grams a year through ingestion and absorption, the equivalent of more than 90 standard 5g lip balm tubes.

Food flavored but not food regulated

The publications point out that lip products are increasingly scented or flavoured like food, with names such as 'birthday cake' and watermelon slice.' These are being targeted towards children and teenagers - among girls aged six to eight in the US, 45% already use lipstick or lip gloss.

With food collaborations and trends in the beauty space on the rise, influencers conduct taste tests of non-edible lip formulations: deliberately consuming the products and reviewing them based on flavour.

Medicines delivered through oral mucosa require extensive preclinical and clinical testing; food additives must clear dietary exposure thresholds. Lip cosmetics, which use the same route of ingestion, require neither.

The reviews also draw on studies identifying microplastics, trace metals and mineral oil hydrocarbons in lip products. In 2022 the EU banned titanium dioxide as a food additive over concerns it could damage DNA after ingestion. It remains permitted in lip cosmetics with no concentration limit and is ubiquitous in lip products including those labelled natural, clean and organic. This is similar for perfumes and ingredients derived from plastics.

The authors do not conclude that lip products are unsafe or safe, but rather illustrate that at modern usage rates, across a dual pathway of ingestion and absorption, the risks are not being accurately assessed.

Laura DiGirolamo, lawyer and beauty industry founder of The Lip Service Alliance and YOM Beauty, said: "Lip products are often made to taste like food and desserts, yet formulated with plastics. Eight or nine in ten conventional lipsticks and glosses contain a plastic. Microplastics are slated to be banned in lip products by 2035, but that is only in the EU, doesn't cover all plastic, and that is 9 years away. While EU regulations acknowledge the presence of microplastics and plastic ingredients in lip products, consumers and parents are largely unaware of this fact, and that is something we look to change with the LSA.

"Children aged six to seventeen spent around 4.7 billion dollars on beauty products in 2023, and lip gloss was the most popular makeup product among them. There are so many ingredients restricted in food yet unrestricted in lip products we know are being ingested, and that is not even considering absorption through thin lip tissue. Nobody has been required to look at what years of that does, and an absence of proven harm is not the same as safety."

Recommendations

The reviews set out a number of key recommendations to address this testing and regulation gap, and build a better picture of lip product ingestion and absorption. This includes:

• Developing lip-specific exposure assumptions that better reflect real-world use patterns.
• Commissioning updated population-specific exposure studies and incorporating those assumptions into regulatory frameworks.
• Mandating testing of lip products on human lip-specific tissue using validated non-animal methods.
• Explicitly considering mucosal permeability alongside skin permeability in safety assessments.
• Using established laboratory models of oral and buccal mucosa, already standard in pharmaceutical research, to screen cosmetic ingredients.
• Providing clearer regulatory guidance that distinguishes lip products from other skin-contact cosmetics.
• Extending the food-grade ingredient principle, already applied by the cosmetics industry's own trade association to mineral oils in lip care, to all ingredient categories present in lip products, with established Acceptable Daily Intake values.

Laura DiGirolamo added: "If you identify a problem without a solution or a pathway forward, you cannot inspire change. We started YOM to prove that a new gold standard for lip formulation can be achieved with the ingestion and absorption routes in mind, and it is proof that the future is bright. But this is not enough on its own. We had to illustrate how real this issue is with robust peer-reviewed research and specialists across several fields. I am proud of what our research teams have achieved with the support of the University of Birmingham."

The Lip Service Alliance hopes that by pointing out this blind spot, consumers will be more aware of the issue, and that cosmetic companies and regulators will do more to close the gap, such as engaging and commissioning more peer-reviewed research, solid data, and exploring solutions so the industry can innovate and change as quickly as possible.

The Lip Service Alliance is inviting the beauty industry, regulatory experts, brands, scientists, universities, influencers, and anyone else who can help create awareness for this issue and help close this gap to get involved.