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THE LAST WORD

Age markerElderly people sometimes develop what are known as liver spots, which are darker areas or blemishes on their skin. Why, and what causes them?

n Tissues such as hair and skin do not produce their own colour; they get that from neighbouring cells called melanocytes through a remarkable process that involves injection of the pigment raw material, melanin, into the cells of the growing tissue.

Fresh melanin is practically colourless, gaining its final colour as the new tissue matures. Even after that, sunlight may cause it to darken further, which is the temporary tanning effect we see in our skins after unaccustomed exposure to strong sunlight.

People, particularly those with certain genetic make-up and who have exposed themselves to a lot of ultraviolet light as they aged, may find some of their melanocytes multiplying or darkening, or both, forming visible patches in the skin tissue. The resulting effect is known as freckles, lentigo, or naevus depending on the details.

Unlike most similar-looking medically important growths, the typical liver spot is flat, harmless and requires no treatment unless for cosmetic purposes.

A medical checkup every year or two, in case a patch is hiding or developing into something more serious, is not a bad idea, but generally liver spots are of

little medical interest except to dermatologists. Jon RichfieldSomerset West, South Africa

Eyes right?Why, when I am tired, does my eyelid sometimes flutter?

n The involuntary muscle contractions that ripple across an eyelid are called myokymia. They appear spontaneously and usually disappear again within a few days, though they can persist for up to three weeks. They are triggered by stress, fatigue or eyestrain, and can be exacerbated by caffeine or alcohol.

Readers familiar with the series of Looney Tunes cartoons featuring a coyote in pursuit of a roadrunner may recall that the earliest cartoons apparently

showed Wile E. Coyote’s facial muscles twitching to convey the stress of being outwitted yet again. The animators were taking poetic licence because, though people with myokymia are acutely aware of the twitching and might even see the fluttering motion in their peripheral vision, it is virtually imperceptible to an observer, as can be confirmed by looking closely at the offending eyelid in the mirror.

Myokymia is quite different

to the erratic blinking that may be a sign of anxiety, particularly in young people. This anxiety can also be manifested as shoulder shrugging and mouth twitching. Sometime between their 7th and 14th birthdays, about 1 in 3 boys and 1 in 10 girls will experience this anxiety and its symptoms.

Intense, longer-lasting and more widespread shaking of the body might indicate caffeine poisoning, alcohol withdrawal, an overactive thyroid gland or Parkinson’s disease. Mike FollowsWillenhall, West Midlands, UK

Lazy powerWhat allows animals such as gorillas and alligators to remain so powerful when they rarely use that power? Alligators, for example, eat rarely and so only have to use their strength to catch prey once every so often. Why don’t they lose muscle mass during periods of inactivity in the way that humans, who have to work out regularly in order to maintain muscle mass, would?

n Gorillas and alligators get plenty of exercise. Gorillas are knuckle-walkers so their arms are in use all the time. They also climb trees, break off branches and tear up vegetation that they eat. Every night they construct a new nest out of tree branches.

The silverbacks are always on the go, keeping the troop together, looking for predators and making the younger males toe the line. As they age they do lose muscle bulk

and become weaker, eventually being replaced by a younger male and being cast out of the troop. From this point on they get weaker and weaker and ultimately die from old age.

Alligators and crocodiles also get lots of exercise: they live on food that they must first catch. Saltwater crocodiles have been found a long way out to sea where they have to swim all the time or sink.

So I suspect that the vision of lazy gorillas and alligators described in the question is incorrect.Hilton SelveyMooloolah, Queensland, Australia

This week’s questionsHAir-brAinEd?I bought some mohair knitting yarn but when I started to knit with it it shed hairs all over everything. Experienced knitters told me that I could solve the problem by putting the mohair in my fridge (but not the freezer) for several hours. I was astonished to find that this works. Why?Pat SlessengerKenilworth, Warwickshire, UK

On THE bOuncEMy fiancé constantly jiggles his leg up and down when he’s sitting. I’ve noticed that quite a few people do this. Why is it so common? And does it burn up calories?Helen ThomsonLondon, UK

“Although people are aware of their eyelids twitching, it is virtually imperceptible to an observer”

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