Shingles (otherwise known as Herpes Zoster) is a painful, blistering rash caused by the chickenpox (varicella) virus, which affects only a limited area of skin, and makes you feel surprisingly tired, run down, and even depressed.

You may feel slightly unwell, and develop a localised area of pain and tenderness a few days or sometimes up to two weeks before the rash appears. The rash starts off as red spots, which quickly turn into blisters. They always affect only one side of the body (left or right) and never cross the midline. This is because they come out on the area of skin which is supplied by one particular nerve.

The rash may affect any part of the body, including head and limbs. It may thus appear as a band around one side of the chest or abdomen, or down an arm or leg. It may affect the head, and when it affects the upper cheek or the side of the forehead it may also affect the eye. You should certainly see your doctor if you have shingles affecting the side of the head, and especially if it seems to affect the tip of your nose or the eye itself.

It is usually a very painful rash, and typically people can't bear clothes touching the affected area.

The blisters burst and crust over, usually within a week and the area slowly settles, sometimes leaving pale scars. The pain may settle as quickly as the rash, but unfortunately some people are left with pain affecting that area for many months or even years (Post herpetic neuralgia).

Most people are surprised by how ill they feel with shingles. This seems out of proportion with the extent of the skin involved. There is a general debility and exhaustion, sometimes with aches and pains and sometimes a mild fever. Depression is often a feature of shingles, as in many other viruses. You may need up to three weeks off work.

You can only get shingles (Herpes Zoster) if you have previously had chickenpox. After having chickenpox the virus lies dormant in the nerves, and shingles occurs when it is revitalised in one particular nerve to the skin, thus explaining the way it affects a clearly demarcated band of skin only.

Usually the cause is a decrease in your body's natural resistance, which may come through other infections, stress, being generally run down, or occasionally, when the body's immune defences are affected by certain drugs or other immune deficiencies.

The pattern of the rash, in the form of blisters usually clinches the diagnosis, but a sample of the fluid from the blisters, or of blood can confirm it. It is unlikely that your doctor will need to do any tests.

The main thing is to take regular pain relief (an analgesic), possibly even better an anti-inflammatory pain killer (non steroidal anti-inflammatory drug), as long as these do not upset you or interact with any medications you may be taking. In addition calamine lotion can help to soothe the area.

Your doctor may want to prescribe a specific anti-viral agent, possibly in the form of treatment to be applied, or in the form of tablets. These are more likely to be used in someone whose eye is affected, or whose immune system is adversely affected by drugs or illness.

If any of the blisters become infected with ordinary germs (bacteria) the area becomes more red and sore (inflamed) and may take longer to heal. The doctor may treat this with antibiotics, in the form of a cream, or by mouth.

If the eye is affected (ophthalmic herpes) or looks like it may become affected, your doctor is likely to ask an eye specialist (ophthalmologist) to see you as a matter of urgency. The treatment is likely to involve specific anti-viral eye drops, and possibly treatment by mouth as well.

In the event of long-lasting pain (post herpetic neuralgia) you should consult further with your doctor, who may try alternative treatments, and sometimes may ask a pain specialist to see you.

You cannot do much to avoid shingles. It is not caught from contact with someone with shingles or with chickenpox.

If you have shingles you should stay away from other people until the blisters have dried (usually about seven days), as there are virus particles in the blister fluid. The risk is that people who have not had chickenpox might catch that from you.

Those at particular risk are people whose immune system is not functioning normally (who are immunocompromised), as for example in people on steroids, chemotherapy for cancer or those with transplants or with AIDS, so do try to avoid contact with people in these categories if you have shingles.

Shingles is caused by a reactivation of the dormant virus in the nerves of people who have previously had chickenpox. As as a result shingles can unfortunately occur more than once.

You may have further attacks of shingles, especially at times when you are run down. These attacks may affect a different part of the body.