Introducing the gut-skin axis

Scientists have shown that the gut microbiome doesn’t just help you digest and support your gut health. 

In this article, we’ll dig into the latest findings about connections between your gut microbiome and skin health.

These connections make up the so-called gut-skin axis.

Skin and gut lining: Not so different

You might not immediately see a connection between your gut and skin, but they do share some features and play similar roles.

First and foremost, they both have large surface areas: 

• your skin: around 270 square feet (25 square meters)

• your gut lining: about 323 square feet (30 square meters)

Also, both are both supported by a dense network of blood vessels, nerves, and immune cells.

For example, your skin helps prevent pathogens from entering your body, as does your gut lining.

And while your stomach produces a famously strong acid to kill “bad” bugs, your skin is mildly acidic, too. It also secretes a lot of salt, discouraging “bad” bugs from proliferating.

Scientists have now shown that an imbalanced skin microbiome is linked with with some skin disorders. This imbalance is called dysbiosis.

Likewise, dysbiosis of the gut microbiome is associated with diseases of the gut and other ailments.

Now, because two areas of the body share similarities doesn’t mean they’re linked. But, in this case, they seem to be.

Skin and gut conditions linked

Scientists have known for a long time that some skin complaints can occur alongside gut symptoms and vice versa. 

For instance, these are two common gut conditions and their associated skin conditions:

• inflammatory bowel disease: psoriasis and atopic dermatitis (eczema)

• celiac disease: psoriasis, atopic dermatitis, chronic itch, and rosacea

Scientists have also noted links between diet and skin conditions, including psoriasis. 

As an example, one study in people with psoriasis found that following a Mediterranean diet more closely was associated with reduced symptoms.

However, it’s worth mentioning that studies examining skin health and diet can be challenging to interpret. 

For example, having a lower-quality diet can increase the risk of obesity, which comes hand-in-hand with inflammation. So, in this case, is the food or the inflammation influencing skin health? 

With that said, scientists are confident that the gut-skin axis exists. But they haven't fully fleshed out how these two areas communicate and affect your overall health.

How do your gut bugs influence your skin?

We don’t have enough evidence to answer this question entirely. But your gut bugs likely influence your skin via different routes, and experts have a few theories. We’ll touch on some of them here.

As such, short-term inflammation plays a key role in the body's natural response to infection or injury.

However, if inflammation continues for long periods, it becomes "chronic" and can cause damage. And many skin (and gut) conditions involve chronic inflammation.

This may be a critical link between your gut and your skin.

Driving or reducing inflammation

Some gut bacteria, including the “good” gut bug Faecalibacterium prausnitzii, produce substances called metabolites that influence the immune system. 

Even pieces of bacteria, such as polysaccharide A, can have an anti-inflammatory effect.

Experts also think that short-chain fatty acids (SCFAs) are important.

Some gut bacteria produce these acids as they feast on the fiber you eat, and SCFAs have a wide range of beneficial effects throughout your body.

One SCFA, called butyrate, has an anti-inflammatory effect, which might benefit your skin. 

However, it’s tricky to unpick how much influence SCFAs from your gut might have on your skin. Scientists still don’t know how much gut SCFA reaches the skin — and it’s likely to vary from person to person.

Also, some bacteria in your skin’s microbiome produce SCFAs, which muddies the water further. 

A more direct influence?

SCFAs in your gut might influence your skin health in other ways. Butyrate feeds the cells that line your gut, helping to keep the lining intact and prevent it from becoming “leaky.”

A healthy gut lining usually keeps bacteria and other unwanted compounds from exiting the gut. If the lining is compromised, they might sneak through into your bloodstream.

Not every participant in the study had bacterial DNA in their circulation, but those who did tended to have had psoriasis for longer and had higher levels of inflammation.

Other gut bug molecules

Besides SCFAs, your gut bugs produce an array of compounds that could potentially influence your skin and other bits of your body. 

For instance, some gut bacteria can produce neurotransmitters, which are chemical messengers that your nervous system uses.

Here are some compounds gut bugs produce that might influence your skin:

• GABA: This may help relieve itchiness. 

• Dopamine: This might slow hair growth.

• Acetylcholine: This may influence how well your skin acts as a barrier.

• Serotonin: This could influence skin coloration.

To be clear, scientists are still only scratching the surface (pun intended) of how these chemicals might influence our skin (if at all). But there's an impressive array of possibilities.

OK, we’ve covered some ways that your gut bacteria may influence your skin. Now, let’s see if the relationship also runs in the other direction.

Can your skin influence your gut bugs?

A fascinating study published in 2018 looked at the effects of exposure to narrowband ultraviolet B light. Dermatologists commonly use this type of light to treat skin conditions.

The researchers found that three light exposure sessions in 1 week increased vitamin D levels in participants’ blood. This isn’t too surprising — sunlight sets off a chemical reaction in skin to produce this vitamin.

But their other finding is surprising. The scientists split the participants into two groups: those who took vitamin D supplements during the winter and those who didn’t.

Although this was a small pilot study, it’s an interesting insight into the two-way communication between the gut and skin.

Could probiotics treat skin conditions?

If a thriving gut microbiome helps support skin health, it makes sense that probiotics might do a similar job.

Although a number of studies in humans have investigated this question, the jury is still out. But there’s some encouraging evidence. 

Human probiotic studies

One study included 80 adults with atopic dermatitis. For 56 days, the participants took either a placebo or a probiotic mixture of three species of bacteria.

At the end of the study, those who took the probiotic had smoother skin, reduced symptoms, and lower levels of inflammatory markers.

Another study recruited 57 people with acne, rosacea, and a form of dermatitis. Some took a placebo, and the rest took two capsules of Escherichia coli Nissle probiotics every day for 1 month.

A different study tested Bifidobacteria infantis — a “friendly” gut microbe — in people with several inflammatory conditions, including 26 people with psoriasis.

The team found that those taking the oral probiotic had reduced levels of inflammatory markers in their blood, compared with people taking a placebo.

Another study recruited 64 women with sensitive skin. The scientists gave half of the participants a probiotic containing Lactobacillus paracasei NCC 2461 and the other half a placebo.

The researchers measured the degree of skin sensitivity using capsaicin — the molecule that makes chili peppers hot. 

They assessed skin barrier function by testing how moist the skin was after comparing an area that had been repeatedly stripped with dermatological tape and an unstripped area.

More water evaporates if your skin barrier is compromised, leaving your skin drier. And if the barrier isn’t as effective, your skin can potentially let through compounds that might irritate or inflame it.

Before we get too excited

Although some of the findings above seem promising, the studies were relatively small. Scientists need to do much more research to see whether, and how well, probiotics might treat skin conditions.

Also, it’s important to highlight the relevance of sponsorship and financial conflicts of interest. 

Many scientists receive their funding from businesses. This is often necessary, and it’s completely above board. However, it’s always important to be transparent about where funding comes from. 

You can imagine that skincare and beauty companies are keen to find evidence that a pill can “keep your skin looking younger for longer.” 

But that’s not to say that probiotics could never help keep skin healthy. There’s just a great deal of science to be done before we can say this for sure.

So, what should you do?

It seems that there are meaningful links between your gut microbiome and your skin.

However, exactly what these links are and how they affect skin conditions is still quite mysterious.

As you’ve seen, the gut-skin axis is hugely complicated and poorly understood. So, if you read incredible claims on probiotic pill packaging, these are likely to be more marketing than science. 

And the best way to look after your gut microbiome is to eat a varied, plant-rich diet, to stay active, and to get enough sleep. 

It may or may not improve your skin, but it’s likely to make you feel healthier overall. We have a handy guide to improving gut health, which might be a good place to start.