Your skin has its own immune system

New, needle-free vaccines could target the skin directly

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It only takes a brief, casual observation of your skin to notice how busy things are beneath the surface. Just think of the spectrum of colours a bruise goes through as it heals, or the way a scab hardens and becomes flaky while a graze is repaired.

It's hard to miss your skin's responses to the bumps and scrapes from your collisions with the outside world. But its efforts to protect you from the microorganisms looking to creep into your body from the outside world are often overlooked. It's all too easy to see your skin as just a barrier - the external walls of your body's fortress - while giving your immune system all the credit for defending it against any intruders that manage to get in.

But recent research has revealed the fortress walls of your body have their own army of defenders. In other words, the skin has its own, semi-autonomous immune system ready to fight off infections at the point of entry.

According to a pair of new studies published in Nature, this system can actively produce the antibodies that counteract anything our bodies recognise as a threat, such as foreign microbes or toxins. Immune responses in the skin are completely normal during an infection. But the discovery that healthy skin builds up its own defence in preparation for an attack is a surprise to researchers.

“It was very exciting,” Prof Michael Fischbach and Dr Djenet Bousbaine, bioengineers at Stanford University and co-authors of the two new studies, told BBC Science Focus. “We already knew that skin microbes could induce one part of the immune system (T cell responses) and that such responses could be redirected against new antigens.

“Our discovery that skin microbes also induced an antibody response (another arm of the immune system) allows us to develop topical vaccines that can be applied to the skin or inside the mouth against diseases such as tetanus.”