The healthy vagina is a complex micro-environment where lactobacilli bacteria thrive, keeping the pH of the vagina acidic, says Mike Emens, consultant gynaecologist at the Birmingham Women's Hospital. "The vagina will normally `perspire' to keep itself moist," he explains. "It is particularly wet mid-cycle, when cervical mucus combines with fluid from the Bartholin's gland at the base of the vagina."
This fluid contains a number of agents to keep the vagina healthy, including a natural antiseptic from the vulval skin glands. Should the bacteria- rich fluid dry up, the vagina's acid balance is altered and its surface cells are destroyed in a "burn", causing soreness.
Women who suffer this imbalance are also more prone to infections such as bacterial vaginosis - the most common reason for vaginal discharge - and thrush. Vaginal lubrication, or the lack of it, is closely linked to hormonal changes, explains Sheila Hancock, advice sister at the Marie Stopes Clinic, London. The female hormone oestrogen is a water-retention vehicle which plumps up tissue, she says; the depletion in oestrogen which accompanies the menopause can cause thinning of the vaginal walls. Childbirth and breast-feeding also trigger hormonal fluctuations which can result in vaginal dryness, as do some contraceptive pills, while sanitary tampons may aggravate the problem. "Don't use them for more than four days in a row, and avoid wearing them at night," advises Mr Emens. And just as hair and skin can suffer during or after illness, vaginal lubrication may also be temporarily interrupted.
But one of the commonest complaints about vaginal dryness relates to lack of sexual arousal. Julia Cole, a psychosexual therapist with Relate, points out that many men and women are ill-informed about the complexities of arousal. "Many couples rush into sexual intercourse after five minutes, but up to 20 minutes of foreplay may be needed for women to lubricate properly," she points out. "If a woman is not ready it can set up a vicious circle of anxiety, insufficient lubrication and painful intercourse."
The picture is further complicated when anxiety or relationship problems make it difficult to relax. "If you are tense or worried you will not lubricate, even if you think you want to make love," says Ms Cole.
What can be done? Menopausal women may wish to consider treatment with oestrogen - whether taken orally or in the form of creams (which avoid the systemic effects of oral HRT). Women who have just had a baby, who have been unwell or who are around menopause, plus some women affected by disabilities, may find temporary use of vaginal lubricants useful. If a woman finds the traditional jelly offputting, a new range of lubricants which imitate the consistency of vaginal mucus may be helpful.
But lubricants should not be used to mask relationship problems, warns Ms Cole. "If you use a lubricant because you don't trust your partner, then you are sidestepping the problems in the relationship."
VAGINAL DRYNESS: WHAT MIGHT HELP?
The following products are water-based and safe to use with condoms. Oil-based lubricants, e.g. petroleum jelly, can seal in bacteria and damage condom rubber in minutes. Senselle vaginal solution. 10ml pounds 1.95; 40ml pounds 4.95. Imitates the consistency of vaginal mucus.
Astroglide lubricant. pounds 6.50 for 2.35oz bottle. Claims to match acidity of normal secretions, encouraging growth of healthy bacteria. Available only from Harlow Lubricants, Freepost NW6052, London NW74YP.
Replens vaginal moisturiser. Relieves symptoms for several days. Three- pack (of applicators) pounds 1.92; 6-pack pounds 3.95. Claims to match acidity of normal secretions. Can enhance growth of cell walls, causing the vagina to thicken. However this can cause "dandruff" from extra cells being shed.
KY lubricating jelly: 42g pounds 2.19; 82g pounds 3.45. Also available in pessary form.Reuse content