How what we put on our skin can prevent or create allergy

What we put on our skin may be as important as what we eat and a new study helps to explain why.

For years, Professor Franca Ronchese, an immunologist working at New Zealand’s Malaghan Institute of Medical Research, has worked to understand how allergies start.

What we feed our skin matters.Credit:iStock

Allergies affect about one in five Australians and these rates are increasing. Although researchers know that allergies occur when the immune system overreacts to certain substances and that there is often a genetic component, much less is understood about what changes in the immune system to cause this response in some people and not others.

Previous research had found that a chemical messenger, called IL-13 is a “key player” in the inflammatory response triggered by a parasite or allergen.

“For example, moulds can contain toxic substances that damage our airways and induce factors that signal the immune system to make IL-13 and that’s what starts the allergic reaction,” Ronchese explains over the phone from Wellington.

What she was surprised to discover however was that, unlike elsewhere in the body, IL-13 isn’t just produced when our skin’s immune cells detect a threat. It exists in our skin all the time.

Why?

Our skin, the largest organ of our body, is often the first line of defence against pathogens – just sitting in a room, we are exposed to about 9000 different species of microbes.

What this means is that the immune response of our skin must be primed at all times to respond quickly to threats, hence why it may be uniquely adapted to IL-13. But, this constant presence can also make our skin more trigger-happy, tipping some people towards allergic disease.

“Having this IL-13 in the skin at all times can predispose us to developing allergies if we are exposed to something through the skin,” Ronchese says of her research, published in Nature Immunology.

“We also know that when the structure of the skin is not completely impermeable… you have an increased risk of allergies – not just skin allergies, but food allergies, airway allergies. That, linked together with this factor in the skin that favours allergy, really adds up to a powerful combination… It’s not surprising that these allergies happen to people who are otherwise fairly healthy.”

And given that the two ways our immune system can be exposed to allergens is via our skin and our mouth, it is not surprising that what we put on our skin is likely to be as important as what we eat.

The key difference is that our guts have evolved to handle a range of foods and because we need food to survive, they are generally more tolerant.

“If our immune system sees the same thing through the skin, the response is different – the skin is trained to react and cause allergy,” Ronchese explains.

This means that using a nappy cream with peanut oil in it, for instance, can result in a food allergy to peanuts but introducing peanut butter – and other potential allergens like eggs – to a baby’s diet from around 4-to-6 months of age helps to create tolerance.

“It is important to encounter new foods by eating them, and after we have eaten them several times it seems to be safe to be exposed to them in other ways, for example the skin,” Ronchese says.

But it’s not just products containing highly allergenic foods that can be a problem for our skin.

Olive oil, when applied as a moisturiser, can break down some lipids (fats) in the skin, disrupting the skin barrier, explains Professor Adrian Lowe, an allergic disease epidemiologist at the University of Melbourne. This may apply to certain food-based products too: “food allergens in topical treatments [can] potentially cause sensitisation and allergy, if applied to the skin, particularly if it is already inflamed/had barrier breakdown occur.”

According to a Cochrane review Lowe was involved with, there is even some evidence that standard moisturisers and those marketed as eczema treatments can potentially increase the risk of skin infections in children’s skin, “possibly because it’s creating a micro-environment on the skin where infectious agents including bacteria and virus can adhere onto skin increasing the likelihood of it being able to penetrate and get a foothold”.

Lowe, who is currently leading a trial on a specially formulated cream called EpiCeram for the prevention of eczema and food allergy, also says strong detergents and powerful soaps “may” break down the skin barrier.

“Care does need to be taken. Not all skin treatments will improve the skin barrier.”

So, given that allergies can develop at any age, what can we put on our skin?

Dermatologists recommend prescription products only for those with allergies.

“No one product is going to be everyone’s panacea and neither is it everyone’s villain,” says dermatologist Dr Shyamala Gunatheesan. “Until we get to a stage where we can swab someone’s skin and say this is what you’re allergic to, it’s a bit of trial and error.”

She explains that, for instance there are studies showing avocado is anti-inflammatory and “very good for IL-13 suppression”, but because everyone’s skin barrier and genetic profile is different it could cause a reaction in certain people.

But Gunatheesan isn’t “too worried” about avoiding food-based products on our skin.

Coconut oil, for example, is “probably not ideal on your face” but it can trap in natural moisture on your body, while products containing the key ingredients of oatmeal, goats-milk or avocado can be soothing.

That said, she would prefer we save our smashed avo for our toast.

“I’m a very big believer of your gut health mirroring your skin health,” says Gunatheesan, the director of ODE Dermatology. “I think you’re going to get way better benefits ingesting it than putting it straight on your skin.”

Professor Lowe agrees.

“Avoiding frequent alcohol consumption and having a rich and diverse diet is probably a very good idea for a whole range of reasons,” he says. “We don’t really have evidence at this point to say that will reduce the risk of having allergy symptoms. But it’s one of those things you happily support even if the evidence isn’t there specifically around allergy.

“Our skin is a really vital organ, and it is immunologically active and the way we care for our skin is likely to have impacts on the rest of our health.”

Tips for protecting the skin’s barrier

Unless we have a true allergy, we can influence our allergenic potential throughout our lives.

Our skin cells replenish every 28 days, Gunatheesan says, and we can support our skin’s barrier by cleansing once a day at night to remove make-up and pollutants, and using an “ideal moisturiser”, which includes a humectant, that draws moisture from outside (for example, hyaluronic acid), an emollient, to soften the skin (like glycerin), and an occlusive ingredient, which traps moisture (like beeswax, mineral oil, or lanolin alcohol).

She also suggests getting into the right actives and spot testing first on the inside of our arm: “A vitamin B is very anti-inflammatory, it’s good for your pores, it’s good to reduce the oil-gland production and vitamin C is an antioxidant.”

Finally, she says: “Gut health really mirrors the skin barrier because the immune cells in our gut do a lot of cross-talk with the skin on our body. Reducing sugar, reducing dairy, reducing gluten – the common intolerances will give us a skin benefit. Drinking lots of water…and sleeping help too. And, once a week, you might do an autophagy fast, so fasting for 13-16 hours lets you replenish those damaged cells… the idea we can heal our body is huge”.

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