HOW SKIN HELPS TO KEEP YOU HEALTHY

THE skin is the largest organ in the body — and now scientists are discovering it plays a key role in our immunity.

This isn’t just because the skin is a physical barrier. It also sends signals of its own to the immune system about attack by infection, using messenger cells that scientists once believed were only found inside the body.

Now they know these delicate signalling mechanisms are also in the skin. But they can decline, causing inflammation — a build-up of inflammatory molecules that leads to skin problems such as dryness, soreness, redness or flaking, and reduced immunity to infection.

This inflammation, or ‘inflamm-ageing’, in the skin is closely associated with ageing (plus sun damage and environmental stress, such as pollution) and damage to the entire immune system (especially in people with diabetes).

The process happens at the same time as our ‘personally tailored’ immunity (the so-called adaptive immune system, with its library of antibodies and other structures that we each build up over a lifetime of exposure to invading infections) begins to fail with age.

To compensate, the innate immune system — which attacks any foreign cell — begins to overreact, producing extra quantities of catchall ‘natural killer’ cells and cytokines in the skin, triggering inflammation.

Meanwhile, there is also a reduction in levels of specialist immune agents found in the skin called Langerhans cells.

‘We know the numbers of them decline, then really drop off sharply at the age of 70,’ says Suzanne Pilkington, a dermatology researcher.

In another affront of ageing, inefficient or non-functioning immune system cells called T lymphocytes hang around in ageing skin and are not replaced.

These cells are meant to be part of our adaptive immune system that preserves a memory of invading bacteria, viruses or fungi that have been fought off in the past, so the body can be alerted to the need to mobilise defences.

But they increasingly fail to recognise enemy invaders, allowing them in, and also occupy space that would otherwise be available to new cells capable of forming new ‘memories’.

T lymphocytes also contribute to the build-up of inflammation.

‘Once you get a lot of these inflammatory molecules, you seem to lose more natural immunity, so you’re more vulnerable to infection via the skin,’ says Dr Pilkington.

‘This decline in skin immunity seems to coincide with conditions such as Alzheimer’s, heart disease and diabetes getting a grip on the ageing system.’

Damage or ageing processes affecting skin immunity mean that mast cells, which are part of the armoury, also mysteriously redistribute themselves next to nerve fibres, as part of a mechanism which is believed to trigger chronic itching.

This little-discussed by-product of ageing causes misery and sleepless nights for many elderly people, even those without diabetes and other chronic conditions.