When 42-year-old Barbara Carter began to lose some of her hair she was not that perturbed. She was expecting her second child, and assumed the hair loss was related to her pregnancy. But then it began to come out in handfuls.

'I would wake up in the morning and it was on the pillow and in my mouth. I used to go to the bathroom and comb my hair and it would just drop off,' she recalls. 'By Christmas 1988, three months before my baby was born, I was completely bald and I had lost every single hair on my body.'

Over the next three years Mrs Carter remained hairless. She tried everything, from drinking herbal concoctions to rubbing her scalp with a glass tube which transmitted a low electrical current, given to her by a hairdresser. Finally she was referred to a dermatologist who prescribed a combination of steroids, scalp lotion and zinc supplements. Now she has a mass of thick rich auburn curly hair.

Mrs Carter's success in regaining her hair is an exception. While steroid treatment helped her - 'the minute I started taking them, the hair just seemed to whoosh, eyebrows, eyelashes, everything' - dermatologists say that people who lose all their hair rarely regain it. Most have to live all their lives with what Mrs Carter experienced for just three years.

What she thought was natural 'moulting' had, in fact, nothing to do with pregnancy. It was alopecia areata, a disease of the scalp in which baldness is patchy. This can develop into alopecia totalis, loss of all scalp hair, or - as in the case of Mrs Carter - alopecia universalis, loss of all body hair. In addition, many women suffer from a condition called diffuse alopecia, where the hair thins markedly.

At least 30 per cent of women suffer some sort of hair loss at some point during their lives. Male patterns of baldness, which can also affect women particularly during the menopause, are caused by ageing, heredity and the action of hormones on the hair follicles. Alopecia is a different condition, however, and while there is no hard evidence that the number of those with the disorder has increased, concern about it among women and the demand for help certainly has. Consultant dermatologists, such as Dr David Fenton, who runs the hair research unit at St Thomas Hospital, London, have seen their caseloads rise over recent years.

The good news is that researchers have now discovered the underlying cause of alopecia and are optimistic that a cure will be available within the next five to 10 years. Already the treatments available, although not successful with all patients, are an improvment on those of the previous decade.

Alopecia is an autoimmune disease, an overactivity of the body's immune system which causes the follicle - the pit on the skin surface from which the hair grows - to 'switch off' and fail to produce. Some people are thought to be more genetically vulnerable than others.

Until recently it was believed that these rogue follicles occurred only in the patches of skin where hair was lost. But in the last six months researchers from Bradford University's department of biomedical sciences and from Leeds General Infirmary have found that the roots of even normal-looking hair on an alopecia patient are abnormal.

'The area where the hair has come out is obviously 'sick',' explains Dr William Cunliffe, consultant dermatologist at Leeds. 'But under the electron microscope, we can also detect a difference between the normal hair you and I have, and the 'normal' hair these people have between the clinically abnormal patches.'

Researchers at Leeds and Bradford believe patients suffering from alopecia may have an unidentified factor in their blood which reacts chemically with the hair roots. This, combined with a genetic predisposition, may cause the hair loss.

While researchers are beginning to unravel the mechanism behind hair loss, quite what triggers it is still not known. Alopecia areata can affect men, women and children alike - anyone from a week-old baby to an 80-year-old.

Stress is thought to be one factor - not the usual stress of home and work, but an abrupt physical or emotional shock which upsets the body's equilibrium. One woman lost all her hair a few weeks after she witnessed her five-year-old daughter being run over and killed. Mrs Carter puts her hair loss down to her desperation, in her late thirties, to have another child. 'I had had one, then I'd had a miscarriage. I was 38 and didn't want to be 40 and having a baby,' she recalls.

The threat that something awful might happen can also trigger hair loss: it is common in prisoners awaiting execution. Marie Antoinette, once she knew she was to be decapitated, did not go white overnight: she merely lost all the dark hairs, while the white ones were left behind.

Many women who have not been through huge trauma lose some hair for no obvious reason, and while there is no evidence that the normal pressures of daily life cause actual baldness, it can result in thinning hair. A small number may suffer hair loss triggered by surgery or a drug injection.

Elizabeth Steel, who set up and runs Hairline International, a support network for those suffering hair loss, believes that stress is the trigger in at least half the cases of diffuse alopecia. Women running a home and holding down a job, particularly if it is a demanding one, are prime candidates, she says. A high percentage of teachers lose their hair.

Whatever the reason, hair loss causes acute suffering. Almost all patients with total hair loss undergo a grief reaction. 'They grieve for their lost hair and that's worrying and upsetting enough,' says Dr Fenton. 'But with alopecia someone can regrow and lose their hair again and again. Repeated grief reactions can be very damaging. Not infrequently people consider suicide and it destroys their social life. It's devastating; it turns the world upside down.'

Many patients would rather lose a leg than their hair. In a survey carried out three years ago by Hairline International three quarters of the 2,000 women who had suffered hair loss said they felt 'less of a woman' and 44 per cent reported that they had felt suicidal.

Mrs Carter says she felt as if she had become a different personality. 'I used to be very self-assured, but after I lost my hair I would ask my husband's advice about the tiniest things. I felt a total loss of confidence,' she recalls. 'I used to think: 'How can anyone fancy me, when I look like this?' I had to wear a wig every day and in the summer it was so hot it was unbearable. Sometimes I took it off at home, but I was always dead frightened someone was going to come to the door. I used to cry a lot.'

Current research is focusing on how to prevent the body's immune system from causing the follicles to 'switch off'. At Leeds, researchers are working on a drug called diphencyprone. Applied as lotion once a week for about six months, it is thought to work as an irritant, stimulating a dermatitis-like reaction. The white blood cells of the immune system switch to attacking the chemical in the lotion, instead of the follicles, leaving the hair to grow naturally. A study of 300 patients who had suffered alopecia areata found that this drug helped the regrowth of an acceptable (though not luxuriant) head of hair in a third of cases, and some hair regrowth in about 90 per cent.

Other researchers are looking at the potential of cyclosporin, used to prevent organ rejection in transplant patients.

While no current treatment is universally successful, some can be helpful. Steroids in one form or another - whether rubbed in as lotions, given by injection or occasionally taken by mouth - are the main treatment. Some women, particularly those with diffuse hair loss, react positively to a lotion called Regaine, a 2 per cent solution of the drug minoxidil, which is normally used in heart treatment. Regaine is only available on prescription and is expensive: one month's treatment costs pounds 30.

General practitioners still see hair loss as a cosmetic problem,' says Mrs Steel. 'Some offer no hope and just tell their patients to get a wig. But treatments have improved in the last five years. There's no miracle cure, but drug companies are putting in research and getting results.'

Strangely enough some people find it hard to adjust to their real hair if it does regrow; refusal to give up wearing a wig is not uncommon. Kathleen Hodge, 51, an alopecia sufferer for several years, prefers her wigs to her own hair, which recently started to reappear. 'I used to spend hours in front of the mirror messing about with my hair and there were times when I refused to go out because I couldn't get my hair right,' she says. 'Now, within a matter of minutes, I can look absolutely fantastic.'

Hairline International, 39 St John's Close, Knowle, Solihull, West Midlands, B93 0NN. Send large SAE for information.