Parsing pediatric contact allergens

By Allison Evans, Assistant Managing Editor, May 1, 2023

It is a common misconception that allergic contact dermatitis (ACD) is rare in children. It’s estimated that it affects up to 20% of the pediatric population. Diagnosing ACD in children and adolescents can be difficult because it often mimics other skin conditions, especially atopic dermatitis (AD) and irritant dermatitis. While the prevalence of ACD is similar in children and adults, pediatric patch tests account for less than one out of 10 patch tests, said JiaDe (Jeff) Yu, MD, FAAD, director of the Contact Dermatitis & Occupational Dermatology Clinic at Massachusetts General Hospital, assistant professor of dermatology at Harvard Medical School, and incoming president of the American Contact Dermatitis Society. “With challenges in both diagnosing and patch testing, childhood cases of ACD are likely underdiagnosed.”

Dermatologists, all members of the Society for Pediatric Dermatology, with expertise in pediatric contact dermatitis and patch testing reveal clues to watch for that should heighten suspicion for ACD as well as common and emerging allergens to keep on dermatologists’ radars.

“You can see contact dermatitis in children as early as three months of age,” said Karan Lal, DO, MS, FAAD, director of Pediatric and Cosmetic Surgery at Affiliated Dermatology in Scottsdale, Arizona. “How can that be when the skin barrier and the immune system aren’t even fully developed yet? Some children have a filaggrin mutation or they’re predisposed to develop eczema and they already have a compromised skin barrier,” he said. “And once you have a compromised skin barrier and you’re using different products and ingredients, you’re more likely to develop contact allergy just because you have a deficient skin barrier.”

Adults vs. children

Children spend a lot more time in play, school, and hobbies than adults do, so they are exposed to a different set of allergens, said Kari Martin, MD, FAAD, a pediatric dermatologist at the University of Missouri Health Care-Columbia. “Kids are much more likely to be playing sports, playing a musical instrument, and making slime than adults. There are so many different aspects of their day that adults don’t encounter, which gives me context as to what their different allergens might be that most adults probably wouldn’t have exposure to.” Typically, adults have to worry more about perfume, makeup, or chemicals in their workplace, whereas a child is likely using fewer products in general, Dr. Martin said. Unless they have eczema — and then they’re using many skin care products, she added.

Even products that are specifically marketed toward children often contain allergens, and they are different from what adults are typically exposed to, Dr. Martin said. “For example, tear-free shampoo and tagless onesies in which tags are stamped onto the back of the clothing, are items that adults would not be exposed to, but children may encounter daily.”

Contact dermatitis or atopic dermatitis…or both?

ACD cannot be connected to a single immunologic phenomenon. Instead, multiple inflammatory pathways contribute to the condition. On the other hand, irritant contact dermatitis (ICD) is not mediated by the immune system. It’s caused by direct injury to the skin by an irritating or toxic substance that does not require prior sensitization and will develop in any individual with enough concentration and exposure time, said Anna Yasmine Kirkorian, MD, FAAD, chief of Dermatology at Children’s National in Washington, D.C. This injury activates the immune system, triggering an inflammatory response. Unlike ACD, ICD is usually confined to the specific location of injury.

“Most pediatric dermatologists probably don’t think about allergic contact dermatitis enough,” Dr. Yu said. “Part of the reason for that is because, unlike in adults, atopic dermatitis is exceedingly common in children. About 20% of all kids have atopic dermatitis. If you ask any pediatric dermatologist what is the number one or two condition that walks through their door, most will probably tell you eczema or acne.”

Atopic dermatitis does not really have an environmental or allergic trigger; most of it is due to dysregulation of the immune system, Dr. Yu explained. “Most pediatric dermatologists are much more likely to think about eczema well before they start thinking about allergic contact dermatitis.”

“Allergic contact dermatitis can also happen in a systemic fashion where it causes eczematous dermatitis over the entire body, making it really tricky to distinguish AD from ACD,” Dr. Martin said. “With kids, I just have to have a healthy dose of suspicion for ACD. When I’m diagnosing a new child that seems to be clear-cut atopic dermatitis, I always have either irritant contact dermatitis or allergic contact dermatitis in the back of my mind.”

Both of those conditions present almost exactly the same way: red, scaly, itchy rashes on the body, Dr. Yu said. “Most of the time a dermatologist will think atopic dermatitis, and they’re not going to be wrong because most of the time it is going to be atopic dermatitis. But there’s really no way to easily distinguish between allergic contact dermatitis and atopic dermatitis unless you do patch testing.”

“If the patient is not responding to treatment,” Dr. Martin noted, “that is another clue for me that it might be due to something external continuing to drive the process, whether that’s ICD or ACD.”

“If the eczema is recalcitrant or if it’s recalcitrant and in a strange location, like eyelid, hand, or genital dermatitis — places that you would not typically expect eczema to persist, this leads me to wonder whether a kid may have eczema and superimposed contact dermatitis,” Dr. Kirkorian added.

“It’s pretty common to encounter both eczema and contact dermatitis because children with eczema are putting on all kinds of creams, and we know personal care products are a common source of contact dermatitis in all people, including children,” she said.

“Lots of babies have eczema on their face because they drool, and so you ask about irritant contact dermatitis. But if it’s really bad and not responding to mid-potency topical steroids, or responds and immediately recurs, that to me is a clue to patch test. Often the culprit is ingredients like cocamidopropyl betaine (CAPB) and lanolin, found in many children’s so-called natural and hypoallergenic products,” Dr. Kirkorian said.

Common pediatric allergens

Although certain allergens continue to lead the pack, new chemicals are frequently being introduced, shifting the pattern of allergen exposure and sensitization. Contact allergies change every few years based on emerging trends and consumer behaviors, Dr. Lal said.

Typical pediatric allergens include nickel, fragrance, cobalt, balsam of Peru, and neomycin. While nickel often tops the charts in studies of pediatric patch test results, Dr. Martin notes that she does not often see many kids with nickel positivity. “Nickel is probably the most widely discussed allergen out there. It’s so common that people know about it, and they usually figure it out and avoid it.”

According to a 2022 retrospective review published in JAAD, a study led by Dr. Yu, over half of children referred for patch testing were diagnosed with ACD — with nickel sulfate, cobalt chloride, and hydroperoxides of linalool as the most common allergens. Of the children tested, 20% had at least one positive reaction to an allergen not on the North American Contact Dermatitis Group screening series (doi: 10.1016/j.jaad.2021.07.030).

"I’m seeing more decyl glucoside, methylisothiazolinone (MI)/methylchloroisothiazolinone (MCI), and cocamidopropyl betaine,” Dr. Martin noted. “These are three of the insidious allergens because they’re in tons and tons of products. It’s hard to find a kid’s shampoo or body wash that doesn’t have one of these three ingredients in it. They are pretty weak sensitizers, however, so people can be exposed to these chemicals over and over again and most people are fine.”

“Propylene glycol is another common allergy we see,” Dr. Lal added. “It’s a surfactant found in a lot of different skin care products that strips the skin to allow ingredients to penetrate better. Oftentimes when we’re treating eczema patients and they develop a rash that’s all over their body and they’ve been using a lot of skin care products, we start thinking about propylene glycol allergy.”

Fragrance allergies are also extremely common, particularly as children enter adolescence and start using deodorant, body sprays, and perfume, Dr. Lal said. In addition to personal care products, candles can also be a source of contact allergy. A lot of candles contain balsam of Peru, vanilla, cinnamon, and other fragrances. “Sometimes kids come in and families are frustrated because physicians tell them to stop using fragrances and they are adamant that they’re not using them. Candles aerosolize the fragrance and a lot of candles have very potent contact allergens,” he said.

Lanolin

While not a new allergen by any means, lanolin is an important allergen to consider particularly for kids with eczema. In fact, lanolin, an oil derived from the wool of sheep, has been designated this year’s Allergen of the Year by the American Contact Dermatitis Society. “Lanolin is a very commonly used emulsifier and moisturizer included in a lot of over-the-counter moisturizing products, including well-known brands,” Dr. Yu said. “These are brands that kids, particularly those with atopic dermatitis or other skin rashes, probably use frequently on their skin. We often switch kids who develop a rash to these products to something more inert like petroleum.”

Slime dermatitis

If you’ve ever watched Nickelodeon in the late 80s and early 90s, there’s a strong likelihood you saw slime — lots and lots of slime. In recent years, slime has made a viral comeback as parents swapped slime recipes via social media. Consequently, slime dermatitis was identified in 2017 and became more prevalent throughout the COVID-19 pandemic as parents looked for at-home activities.

Slime ingredients can vary based on the recipe but include both potential irritants and contact allergens. The base ingredients include a detergent, such as shampoo, soap, or laundry detergent, in addition to boric acid, which are both causes of ICD. Most slime recipes also include glue which can contain numerous contact allergens, including isothiazolinones. Many of the potential allergens in slime are not on the T.R.U.E. Test but have been listed in the Pediatric Baseline Patch Test Series. (See “Meet the patch tests” below.)

Isobornyl acrylate

Isobornyl acrylate, Allergen of the Year in 2020, is a chemical used in glues, adhesives, coatings, sealants, inks, and paints. Now a known component of medical devices including glucose monitoring systems and insulin pumps, these devices have been increasingly implicated as sources of irritant contact dermatitis and ACD in diabetic patients. It’s thought that diffusion of the glue affixing the needle to the plastic on the glucose sensors causes contact allergy. Other allergens found in diabetes devices include ethyl cyanoacrylate, N,N-dimethylacrylamide, and colophony.

Over the last five years or so, isobornyl acrylate has gone from an allergen that nobody has heard of to one that is widely considered, Dr. Yu said. “It’s different in that it’s not something that you’re going to find in everyday use. You’re not going to find it in your hair products. You’re not going to find it in your toys or other household products, which can make identifying it easier.

Once a new contact allergen has been uncovered through a typically laborious process, reporting on that allergen can have a significant affect, said Dr. Yu, as some manufacturers change their materials. “Sometimes switching to a different adhesive brings more problems because suddenly this new adhesive with this new chemical is actually more allergenic than the old one. But more often than not, when companies switch to something else, cases start to fall. That’s what we’ve been seeing with the glucose monitors,” he explained.

Limonene and linalool

Limonene and linalool are natural terpenes found in essential oils, fruits, trees, grasses, and tobacco. Oxidation of limonene and linalool results in allergenic hydroperoxides that have been increasingly implicated in pediatric ACD. While they are often found in personal care products and detergents used in children, they are not included in Fragrance Mix I or II allergens; they must be tested separately.

Linalool has been found in 90% of common essential oils, which are frequently applied directly to the skin or diffused, in which case they may cause an airborne contact dermatitis. Testing of limonene and linalool alone is unreliable in detection of ACD; their hydroperoxides must be included in patch testing to yield relevant data, Dr. Martin said.

A JAAD review found that among patients who tested positive to limonene and linalool, more than half also tested negative to Fragrance Mix I/II or balsam of Peru. Many patch testing experts recommend that the hydroperoxides of limonene and linalool should be tested in anyone suspected of having fragrance allergy.

“If you have a linalool allergy, you have to know that it could cross react with limonene or other fragrances,” Dr. Martin said, “and to avoid not just the word ‘linalool’ in the ingredient list, but all the other things that could cross react.”

When to refer a patient for patch testing

According to Dr. Yu, there are three general rules of thumb for when to refer a patient for patch testing. First, if a patient has what looks like eczema, but is in a really unusual distribution. “In very young children, having eczema on the face is not uncommon. But if I have a 15-year-old that has never had eczema before in his or her life and suddenly gets eczema on their face, that’s a reason to patch test because that location is unusual, and that history is unusual.”

“If I have a kid who has eczema, say, only on the tops of their feet, only on the backs of their hands, only on their hips, only on atypical locations that do not usually fit the clinical description and morphology of atopic dermatitis, then I would say this person probably has allergic contact dermatitis,” Dr. Yu added, “which may be a standalone diagnosis or maybe it’s paired together with atopic dermatitis.”

Lastly, if an AD patient has traditionally been doing well on a regimen of moisturizing and topical steroids for two years and the patient suddenly starts getting worse, even though nothing has changed, Dr. Yu recommends patch testing that patient. “Typically, with AD, it mellows out a bit over time, rather than exacerbating.”

When patch testing isn’t feasible or may be difficult for a particular patient, often a skin elimination diet is effective. “Once I see what my patients are using, I give them my recommendations for safe products I want them to use instead. I can get most of my patients clear this way,” Dr. Lal noted.

“I often do a three-month trial of changing products, treating, and then seeing what happens. If things don’t improve, I have no problem patch testing. It’s a very underutilized modality,” he said. “But I also think that rather than just ordering patch testing all the time on everybody, you have to be realistic about access issues, like insurance coverage.”

“When a pediatric patient has an eczematous process, it’s important to consider ACD, as the data show it’s more common in children than we think,” Dr. Kirkorian said. “If we ask the right questions, we’ll gain valuable information to guide treatment.”

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