Don't be hit by a pucker punch...

THE skin on your lips is thin because it has to be flexible enough to form words and make facial expressions - and there's the small matter of eating, too.

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The top layer of the epidermis, the stratum corneum, on the lips is made up of just five layers of cells. This compares to the usual 16 to 20 layers in the skin on the rest of your face.

As a result, you can see the colour of the blood circulating in the tiny vessels underneath. And it is one reason lips can be such a useful guide to your health, as we see here...

BLUISH/PURPLE LIPS:

When everything is working as it should, your lips have a healthy pink hue. Blue lips are one of the first signs that your oxygen levels are dropping.

Gerard Lambe, a plastic surgeon, says: "Oxygen-rich blood is bright red, which gives lips their healthy pink colour through the thin skin.

"When oxygen levels drop, the blood becomes much darker and bluish. So, if you're struggling to breathe, the lips can turn a purplish blue. That's a clear sign that something's wrong, often linked to conditions such as pneumonia or other breathing problems."

In the longer term, bluish lips may also be a sign of anaemia, a shortage of iron needed to make haemoglobin, the protein which gives blood its bright red colour.

SWOLLEN LIPS:

If lips come into contact with a food which is an allergen, they may also swell up. This is because the immune system overreacts by releasing chemicals called histamine into the bloodstream.