Almost all 'natural' skincare products sold at three top retailers in the US contain allergens, according to a study from a trio of dermatologists at the Stanford University School of Medicine.

Nearly 90 percent of the 1,651 personal skin care products studied – including lotions, soaps, and moisturizers – contained at least one of the top 100 most common allergens known to cause contact dermatitis.

Contact dermatitis is more than a fleeting irritation. It's a red, itchy rash that, at its worst, can blister, caused by exposure to substances that either irritate or inflame the skin. The latter is an allergic reaction that occurs once the skin becomes sensitized to an otherwise harmless substance.

According to some estimates, rates of contact dermatitis are on the rise worldwide, up almost three-fold in three decades since 1996.

The researchers say that this uptick in contact dermatitis, a rapidly growing skincare and beauty industry worth billions, and a lack of regulation on its marketing motivated the study.

"The US Food and Drug Administration (FDA) has not defined clean or natural, allowing sellers to freely advertise with these terms that imply safety and health benefits," dermatologist Peter Young and his Stanford University colleagues explain.

So researchers extracted product ingredient lists from the websites of three US retailers and checked them against an online database that lists common ingredients people with contact dermatitis should avoid. The American Contact Dermatitis Society maintains the database.

Contact dermatitis is preventable, so long as you can navigate and interpret the long list of ingredients found in skincare products and know which ones might aggravate the skin. Easier said than done.

A typical skincare or cosmetic product may contain anywhere from 15 to 50 ingredients. Research suggests people could be applying over 500 different chemicals to their skin each day, depending on their skincare routine.

In other words, the more products you use, the more you expose your skin to potential allergens.

Many of the allergens identified in the study were fragrances – think lavender and other botanical extracts – which have become a leading cause of contact dermatitis.

On average, skincare products contained between four and five known allergens. In total, 73 different allergens were listed 7,487 times across the 1,651 products studied.

That's only based on product information available online, but it still gives you a sense of the scale of the problem.

"These results suggest a need to educate patients and health care professionals to ensure the public is informed about the products they apply to their skin," Young and colleagues conclude in their paper.

Of course, this isn't the first study examining allergens in personal care products. In 2017, another US study found few moisturizers were free from allergens, and even 'fragrance-free' products sometimes contained fragrances, which can irritate the skin.

The issue has been on dermatologists' radar for some time, but their message rarely seems to cut through the marketing buzz around natural products – which often emphasizes what supposedly harmful ingredients products don't contain, hoping savvy consumers don't scrutinize ingredient lists too closely.

Also, labeling products as 'natural' tells consumers nothing about an ingredient's safety. Instead, it perpetuates a false divide between ingredients that can be sourced from nature and synthetic compounds that could be identical, chemically speaking.

'Natural' is just a marketing catchword that plays on a long history of humans sourcing traditional medicines and cosmetics from nature, making us think these are somehow safer.

But marketing sways consumers' perceptions, and this can have real consequences. An " epidemic" of contact allergies erupted, for example, when a more allergic preservative called methylisothiazolinone started replacing another safer perseverative, parabens after they fell out of favor with the beauty industry because of now-refuted claims based on very shaky science.

That's not to say all marketing is trouble, though it is often misleading and, at times, untruthful. Some beauty influences have contributed to a real shift in sentiment towards sunscreen, now a 'must-have' for good skin.

But terms like 'hypoallergenic' and 'dermatologist tested' are concocted by the industry to give an allure of medical credibility when there are no legal criteria that manufacturers need to meet to make these claims. And that's before we get to how marketing touts skincare's health benefits.

"Both consumers and physicians should demand that the clean beauty movement back up their claims with evidence," two dermatologists at the University of Pennsylvania, Courtney Blair Rubin and Bruce Brod, wrote in an editorial in 2019.

The same is true today.

The study was published in JAMA Dermatology.