A Question of Health: The bane of my sex life

I GET cystitis whenever I have sex. Help!

There are a number of things you can do to try and prevent cystitis after sex. You should empty your bladder before intercourse, and empty your bladder again soon after intercourse. For some women this solves the problem without any further treatment. If you use the diaphragm for contraception you should probably change to another method, because diaphragms can increase the risk of cystitis by putting pressure on the urethra - the tube which connects the bladder to the outside world. You should increase your fluid intake to make your urine less concentrated. Drinking cranberry juice also helps to prevent cystitis. You should also see if any particular sexual positions make the problem worse and avoid these.

If all these things fail, some women can only prevent cystitis by taking a single dose of antibiotics whenever they have sex. You will need to discuss this with a doctor, and at the same time you should have a urine test to confirm the cause of your cystitis and rule out any other diseases such as diabetes.

MY DAUGHTER is ill with chickenpox, and I am worried that I may catch shingles from her. Is this possible?

Shingles and chickenpox are both caused by the same virus - the varicella zoster virus - which is a member of the herpes family. It is not possible to catch shingles from someone who has chickenpox, although it is possible to catch chickenpox from someone who has shingles. More than 90 per cent of people develop chickenpox in childhood and it is usually a relatively minor disease. But the virus that causes the chickenpox infection can remain in the body in a dormant state for many decades. If it "reawakens" - because of reduced immunity - it causes an attack of shingles, which is usually a painful rash affecting a single area on one side of the body, such as the forehead, or back and front of the chest. But you can only "catch" shingles from the virus that originally caused your own attack of chickenpox.

WHY ARE prescriptions free for people with diabetes, but not for those with asthma?

The NHS decided years ago that it would provide free prescriptions for patients who were suffering from "deficiency diseases". This included any diseases caused by the human body's inability to produce natural hormones. People with diabetes are not able to produce enough insulin, so the NHS provides it for them in the form of free prescriptions. Asthma is not caused by a specific hormone deficiency, and people who use inhalers have to pay for their prescriptions.

The rules about who receives free prescriptions are hopelessly out of date, but no one seems very keen to update them. Why, for example, is hormone replacement therapy not free? It is a classic example of a "deficiency disease".

Please send questions to A Question of Health, The Independent, 1 Canada Square, Canary Wharf, London E14 5DL; fax 0171-293 2182; or e-mail to health@independent.co.uk. Dr Kavalier cannot respond personally to questions