What’s making me want to scratch?

FOR the past four months, I have been suffering with itchy skin all over my body. I have red spots, which are mostly small, but occasionally, I get large hives.

A blood test showed nothing. Do I have to suffer for ever? I am 77. John Keers, Truro, Cornwall.

You are not alone — one study on chronic itching, defined as itching that persists for more than six weeks, found that it affected 16 per cent of people.

Pruritus (the medical term for an itch) is a symptom, rather than a disease, and is a feature of a number of skin disorders, as well as seemingly unrelated chronic illnesses, such as kidney disease or thyroid problems.

The blood test you had seems to have excluded the possibility of a chronic disease in your body.

Given the description you have provided and your age, I believe you are suffering from general dryness, known as xerosis, as a result of normal skin ageing.

Just as our muscles waste away and hair naturally thins, skin gets drier as we age. That’s because the outer layer of our skin — the epidermis — thins, and skin loses its ability to retain water.

A reduction in the production of sebum, the skin’s natural moisturiser, in older skin also encourages dry, itchy skin and eczema.

Excessive bathing and central heating can make this worse.

As you say in your longer letter, your doctor has prescribed a moisturiser for you to use daily. I believe that this is critical and you should adopt it as a longterm strategy.

Moisturise your entire body — not just the areas that feel particularly dry — because it will all be vulnerable to becoming itchy, since the cause is generalised skin ageing, rather than a certain trigger in particular areas that may seem more dry.

KEy agents you should look for in an effective moisturiser are liquid paraffin (for example, Diprobase Emollient Cream, which is available at most chemists for less than £10), which has been proven to help, as well as glycerol and povidone (oilatum Cream, for example, contains both these ingredients and is available at most chemists for around £10), which will help form a gel layer on top of skin, helping it to retain moisture.

Continue to use the moisturiser at least twice daily — and avoid washing with soap, which can aggravate vulnerable skin.

Instead, use a soap substitute such as Dermol 500 Lotion, or aqueous cream, either of which should be applied to dry skin before showering or bathing.

you also describe episodes of urticaria, or hives, where there are intensely itchy spots — red with pale centres — that may enlarge then fade within hours. In many cases, the causes are poorly understood, but this may be the result of an underlying allergic response, so you may find that an antihistamine helps.

These work by blocking receptors on the nerve fibres in the skin that have a role in transmitting the itch sensation to the brain and make the itch worse.

you can buy antihistamines over-the-counter, but you should first discuss this with your GP, as antihistamines can cause daytime sleepiness as a side-effect, which may be hazardous. If it is suitable, my preferred choice for urticaria is a prescription-only antihistamine called fexofenadine.

High doses may be necessary, and often patients with this condition need a 180mg tablet twice daily for weeks, or months, to suppress the eruption.

I am sure your doctor will advise but, for now, keep slathering your skin with an effective moisturiser. WHEN I had a dental descaling, the dentist used an anaesthetic gel, which I understand contains benzene or a related chemical.

As benzene has been linked to leukaemia, is there a risk in using these gels? Name and address supplied. your anxiety — provoked by the fear that anaesthetic gel, which I assume is benzocaine, seems to contain benzene — is understandable. But be assured that there is no such risk from your descaling treatment, nor any anaesthetic gels. A short tutorial in chemistry will help in understanding why.

Benzene is a natural component of crude oil and is also found in cigarette smoke. It is made up of six carbon atoms bound together tightly in a ring — and each carbon atom has its own hydrogen atom hanging off it.

This structure has allowed benzene to be used in the manufacture of many materials — including plastics, pesticides and pharmaceuticals — essentially because there are lots of ‘ends’ that other chemicals can react with and attach to.

Crucially, as soon as the chemical structure is altered in any way, its properties change. That means the materials that are made using benzene do not carry the risks of benzene as you know it.

used in its natural state, benzene is known to cause cancer. That is, if you drink it, inhale the vapour, or are exposed to it over a long time, it has been shown to increase the likelihood of leukaemia and other blood disorders.

That’s because it has a toxic effect on the bone marrow — where blood cells develop.

But the materials derived from benzene — which are as varied as polystyrene to paracetamol — do not carry this risk.

It is the same with other chemicals, too. For example, sodium is a highly explosive and dangerous metal in its natural state — but sodium chloride is the chemical name for table salt — and all it took was a chemical reaction to attach a chlorine atom to change it into a completely different material, which is clearly not explosive.

Even water, which is formed by reacting two gases — oxygen and hydrogen (which, in itself, is explosive) — bears no resemblance to either. That’s chemistry for you.

I suspect what has worried you are local anaesthetic gels that contain the drug benzocaine.

This drug has a benzene ring as part of the molecular structure, but it is so substantially altered that it is not toxic in the way that the distant ancestral relative benzene is.

THE only note of caution for local anaesthetic gels is that if you swallow large quantities, you risk anaesthetising the back of your throat, the upper part of the gullet and even the larynx (voice box) and trachea (windpipe) — this may lead to suppression of your cough reflex for a short period while the anaesthetic lasts.

But you’re unlikely to swallow sufficient amounts during dental descaling. In short, I reassure you: there is no dangerous benzene as such in anaesthetic gels and no risk of cancer from their use.

you can relax and continue your dental care.