Throughout her 30s, Marie Cuthbertson, now 50, sought help for embarrassing and painful symptoms after sex.
Each GP she saw said it was a sexually transmitted disease, and prescribed antibiotics.
"All the doctors dismissed out of hand my suggestion that I was suffering a physical reaction to sex," says the married mother of a teenage son.
"They said such things did not happen and implied my partner could have been unfaithful - which was insulting to both of us."
Marie and her husband Mark, 49, who live in Sheffield, did their best to treat the problem "as a joke" and continued trying to enjoy a sex life.
However, her "awful" vaginal pain and inflammation continued, convincing Marie she was having a reaction to the act itself.
"The inflammation and discharge only flared up in the hours afterwards. I was sure the problem was not an infection."
Finally, ten years ago, a new GP referred her to a hospital genitourinary clinic.
"The doctor was fantastic," she recalls.
"I told him I believed I was allergic to sex. He said that he had read clinical reports saying this definitely does happen."
He said Marie could be allergic to semen and that condoms were the only solution. Sure enough, her distressing symptoms disappeared.
"We didn't want to be using condoms, but the solution did work," she says.
Marie's problem might sound rare, but as many as one in ten women may suffer from it.
The reactions may be mild (irritation, itching) but can be so severe as to cause a life-threatening allergic reaction called anaphylactic shock. It has also been shown to spark asthma attacks.
It seems absurd for people to be allergic to semen, the basis of human reproduction.
Nevertheless, Dr Michael Carroll, a lecturer in reproductive science at Manchester Metropolitan University, says his unpublished research indicates that up to 12 per cent of women may have the condition.
He says doctors often misdiagnose the symptoms because of their similarity with other conditions such as dermatitis and some sexually transmitted diseases. Women aged 20 to 30 are thought to be worst affected, displaying reactions immediately, or up to an hour, after sex. Those with the allergy react adversely to all men's semen.
Australian scientists believe this sensitivity could be a factor in another common and often debilitating condition - endometriosis, which causes painful or heavy periods. It is estimated to affect one in ten women of reproductive age in the UK.
Endometriosis is caused by the endometrial cells lining the womb migrating to the ovaries, the lining of the pelvis behind the uterus and the top of the vagina.
It is also linked to infertility, with up to half of infertile women having the condition, says Endometriosis UK, adding that the cause is unknown and has no cure.
But how could this allergy be linked?
In a new study Dr Jonathan McGuane, a researcher in genetics and reproduction at the University of Adelaide, found that mice were far less likely to develop endometriosis if they were born with a gene that left them with low levels of a protein called Transforming Growth Factor-1 (TGF-1) in their wombs.
Human semen is rich in TGF-1. To discover if this could promote the development of endometriosis, Dr McGuane transplanted human womb tissue into specially bred, germ-free mice, then exposed the tissue to seminal fluid. Within two weeks, the grafts grew unnaturally in the womb and started shedding cells - which is how endometriosis spreads.
Professor Sarah Robertson, an immunologist and one of the lead authors of the study, says such problems may be caused because seminal fluid creates changes inside women's bodies, for instance, to help conception.
"In most cases, such activity contributes to setting up an environment which is receptive for the implantation and growth of the embryo," says Professor Robertson, a global pioneer in the study of how seminal fluid affects women.
Her research, published in the journal Immunology in 2012, found that TGF-1 changes the lining of the womb so it becomes more fertile and more immune to infection.
"There may be a flip-side to such effects," she says.
Research is still in its early days and there are other known risk factors, such as a family history.
It is not only women who can suffer. In rare cases, men can be allergic to their own semen. Symptoms include a flu-like illness, with pain, redness and discomfort affecting the head, eyes, nose, throat and muscles, extreme fatigue and difficulty concentrating.
One case, reported in March in The Journal Of Sexual Medicine, involved a Chinese man whose skin broke out in rashes when exposed to his semen. Doctors at the Peking Union Medical College Hospital could identify no cause.
Research four years ago, by Dutch investigators in the same journal, identified 45 men with the problem.
The symptoms occurred only after ejaculation, indicating the men were protected so long as the fluid remained in their testes.
Scientists are still in the early stages of finding what causes such reactions, but a previous allergy to a pet dog may be a factor.
Three years ago, Dr Heinz Kofler, a consultant dermatologist at the Tyrol Allergy Outpatient Clinic in Austria, reported a 25-year-old woman developing swollen eyelids, a rash across her body and breathing trouble immediately after unprotected sex.
Dr Kofler's tests showed she was sensitised to human seminal fluid and to dog dander (tiny flecks of skin). She confirmed she was allergic to male dogs.
The link, says Dr Kofler, is that an allergen in dog dander (the protein Can F5) is chemically similar to the human prostate-specific antigen found in semen and the immune system can confuse the two.
The finding supports two other authoritative journal reports, from allergy experts at the University Hospital Nuestra Senora de Candelaria in Tenerife, and the University of Cincinnati College of Medicine.
The Cincinnati investigators studied 165 women with semen allergy and found that their symptoms were significantly worse if they were also allergic to dogs. This finding suggests that exposure to the pets either sparked the allergy or made it worse.
Common lubricants may also sensitise women to develop an allergy to semen. In January, allergy experts at the Heidelberg University Hospital said lubricants containing methylisothiazolinone may be a risk.
They warn that the widely used preservative has been associated with sparking allergic reactions to semen.
Doctors are still developing ways to help women. Korean doctors reported in 2011 that they had helped a 33-year-old woman with severe allergic reactions to semen, including breathing trouble, to become pregnant by giving her antihistamine tablets to take one hour before making love.
Doctors at St Mary's Hospital and the Department of Immunology at Central Manchester University Hospital, meanwhile, reported in the journal Human Fertility in 2013 that women with a high risk of anaphylactic shock from the allergy can be made pregnant by removing their partner's sperm from the fluid and then implanting it.
Dr Michael Carroll, the reproductive scientist who led that study, says he has since been contacted by women all over the world with the problem.
He said a desensitising treatment is being developed which begins by introducing very diluted seminal fluid via artificial insemination and then steadily increasing the concentration until the woman can tolerate it at normal levels.
Mystery remains, however, as to which components in the fluid cause the allergy.
"There may be several unique proteins responsible," he says, adding that research, linking the allergy with endometriosis, was "exciting" but that much more testing was needed.
• Marie Cuthbertson is a pseudonym.
- Daily Mail