Smell is the most reminiscent of the senses — all those associated memories that come flooding in as soon as a whiff of a certain something wafts under your nose. Studies have even suggested that our noses are important when it comes to choosing a mate. Yet a worrying anomaly has been unearthed in recent scent tests, highlighting a possible side effect to one of the most important pharmaceutical discoveries of the past 50 years: the contraceptive pill. Yes, that little pill, which was introduced to Britain in 1961 and has allowed women sexual freedom, may also be disrupting their instinctive ability to choose a man.

The issue was first raised during the aptly named “sweaty T-shirt study”, undertaken by the Swiss scientist Claus Wedekind in 1995. The theory was based on the well-known theory that opposites attract. Mammals are thought to choose partners with genetic dissimilarities, thereby maintaining a diverse gene pool. We are programmed to prevent inbreeding, not only by incest taboos and laws, but, most fundamentally, biologically. It all comes down to a group of genes called the major histocompatibility complex (MHC), which encodes a set of proteins that are central to determining the strength of the body’s immune system and affect body odour by interacting with bacteria on the skin. The premise of the experiment was simple: a group of men wore the same T-shirt for a couple of days, forgoing deodorant, scented soap, spicy foods and sex. Their T-shirts were then presented to a selection of lucky ladies who had to grade them in for sexiness. Wedekind proved his thesis: the women chose the T-shirts worn by men with dissimilar MHC to themselves. What he did not predict, however, was the effect oral contraceptives would have on the experiment.

The T-shirt-sniffing test was repeated this year in a joint study by scientists from Liverpool and Newcastle universities, but this time the subjects were tested before and after using the pill. Dr Craig Roberts, a specialist in evolutionary psychology at Liverpool University, claimed the results proved that women on the pill were more attracted to men with “genetically similar odours”.

Wedekind has suggested a reason for this biological blip: “My guess is that the pill simulates pregnancy and that odour preferences may change during pregnancy.” It is thought that pregnant women are naturally predisposed to those with similar MHCs to their own, such as family members, because those people would be more likely to protect the woman during pregnancy.

The implications of this discovery are huge. Roberts has suggested that “not only could MHC similarity lead to fertility problems, it could lead to the breakdown of relationships when women stop using the contraceptive pill, as odour perception plays a significant role in maintaining attraction to partners”. In other words, by meeting their future partner while on the pill, women could unwittingly be ruining their chances of having children.

Louis Weckstein, IVF and medical director at the Reproductive Science Center, in California, found that couples seeking IVF treatment were less likely to conceive if they shared too many MHC genes. The risk continues even after conception. Carole Ober, of the University of Chicago, carried out a study of the links between MHC and miscarriage. She found that couples with higher genetic similarities were more likely to miscarry.

There are also potential repercussions for marital happiness, beyond the stress of attempting to conceive. Roberts carried out a smaller study that found women were more likely to commit adultery and complain of sexual disappointment if their partner was MHC-similar. It may just be a coincidence, but I only found my current boyfriend attractive when I came off the pill.

Not all scientists are convinced of the importance of olfactory awareness when choosing a mate. Many of the studies carried out prior to this year were conducted on rodents. It has been suggested that we are incapable of scenting the intricate nuances of other humans because we don’t have the developed nasal organs that rodents possess, which are necessary to detect olfactory signals. Wedekind does point out that “women are usually more sensitive to body odours than men”, which would explain the female-centric nature of his studies, but no research has been published on whether taking the pill affects a woman’s attractiveness to a man.

Still, it is discomfitting to think that the pill, which has become an integral part of so many women’s sexual lives — 25% of 16- to 49-year-old British women are on it — could actually be altering their choices when it comes to the most important relationship in their lives: a long-term partnership.

The question is: are you ready to come off the pill and discover if you are still attracted to the man you are cuddling up to?

Times recommends

• Psst! It’s so easy to spy on the wife
• News Review interview: Sheryl Gascoigne
• Scientists discover true love