Stable gut, happy skin?

The gut and skin share common features: both act as barriers to the outside world, protecting harmful substances from reaching the internal environment of the body; and both are lined with their own community of microbes (known as the microbiota). These microbes help keep our bodies healthy, such as protecting us from harmful microbes and extracting nutrients [1]. Along with its microbiota, the inner workings of the gut can impact the skin. Here, we explore how the gut can influence skin health and disease.

How the gut 'talks' to the skin?

In a 'stable' state, gut cells link together and form a strong barrier against harmful microbes and molecules. As with the skin, the gut is also supplied with a variety of immune cells ready to clear any harmful microbes that break through the barrier. But this barrier must allow nutrients in, so the gut barrier loosens or tightens to regulate the flow of substances to the tissue and blood vessels on the inside of the body [2]. Once substances enter the blood, they can reach and affect distant sites in the body, such as the skin. A range of substances influences the skin, including products released from the microbiota and immune and gut cells [3].

Keeping the skin happy

The gut may play a part in keeping the skin healthy through many different processes. For example, the gut microbiota can contribute to wound healing by helping gut cells absorb molecules that aid skin repair, or by directly releasing these types of products themselves [4]. The gut microbiota can also restore skin to a healthy state after damage, re-establishing appropriate immune response levels in the skin after UV exposure [5]. Animal studies have shown that supplementing the gut microflora can also improve skin thickness, flexibility and hydration [1].

Once substances enter the blood, they can reach and affect distant sites in the body, such as the skin. A range of substances influences the skin, including products released from the microbiota and immune and gut cells.

How does the gut influence skin conditions?

The diversity of the gut microflora, the relative proportions of different species, and/or their contact with the immune system may influence inflammatory skin conditions, such as psoriasis and eczema. Changes in the gut microflora can generate products that activate immune cells, which could cause inflammation in the skin [3]. The gut microflora also generates products that are anti-inflammatory and strengthens the gut barrier, such as short-chain fatty acids [6]. Short-chain fatty acids were found to be relatively low in some eczema cases [7], suggesting further investigation is needed into the role of the microbiota and these substances in eczema.

Complex gut–brain interactions may play a role in inflammatory skin conditions, such as acne. Under psychological stress, such as anxiety and depression, chemicals that activate neurons can be released from the gut. These chemicals loosen the gut barrier and move through the barrier into the blood, where they circulate around the body and can cause inflammation in the skin [1] — highlighting the complex interplay between the gut and distant regions of the body.

Conclusions

The gut may influence the skin in a variety of ways, from helping repair wounds to stimulating inflammatory responses. With complex systems involved, the full impacts on skin are still being revealed. Surprisingly, a more in-depth look at our gut may shed light on new ways to care for our skin.