In 1995, Swiss biologist Claus Wedekind conducted an experiment that became a classic of behavioural genetics. He asked 44 men to wear the same cotton T-shirt for two consecutive days — without deodorant, without fragrance, without strongly scented food. Then 49 women smelled the T-shirts and rated each for 'pleasantness' and 'sexual attractiveness.'
The result was unexpected: women preferred the smell of men whose HLA genes (Human Leukocyte Antigen — the human immune system's identification system) differed most from their own. Some women also noted that the 'pleasant' smell reminded them of former partners or close relatives. This too turned out to be a pattern: women taking oral contraceptives selected scents from men with similar HLA profiles — that is, closer to kin rather than further away.
HLA is a system of proteins on the surface of cells that allows the immune system to distinguish 'self' from 'non-self.' These proteins recognise pathogens and trigger immune responses. The HLA system is one of the most genetically diverse in humans: thousands of gene variants exist, and every person has a unique combination.
The evolutionary logic of preferring a dissimilar HLA is straightforward: a child who inherits different HLA variants from each parent will have a broader immune repertoire. They will be able to recognise and neutralise a wider range of pathogens. This is not abstract theory — it is a confirmed evolutionary advantage.
How scent carries HLA information: The molecules that shape individual body odour are partly determined by the skin microbiome. And the composition of the microbiome, in turn, depends on the host's immune profile — including HLA. Body odour is thus literally a chemical 'summary' of the immune system. We read it through our noses — unconsciously.
Wedekind's finding has an important practical implication. Oral contraceptives simulate the hormonal profile of pregnancy. In that state, it is evolutionarily advantageous to be close to genetically similar people — relatives who would provide support. Hormonal contraception appears to shift olfactory preferences in the same direction: toward genetically similar partners.
This creates a real-life scenario: a woman meets a man and falls for him while taking contraceptives. When she stops — for instance, to conceive — her partner's smell may begin to seem less attractive. His actual HLA profile is no longer 'hidden' behind the hormonal shift.
Most mammals have a vomeronasal organ (Jacobson's organ) — a specialised structure for detecting pheromones. In adult humans, the vomeronasal organ is either absent or present as a rudiment with no functional neural connections to the brain.
This does not mean humans do not respond to chemical signals. They do — but through the ordinary olfactory system, not through a specialised pheromone channel. The molecules androstadienone (found in male sweat) and estratetraenol (in female urine) have been studied as possible human pheromones — with mixed results. No scientific consensus has been reached: human pheromones in the classical sense remain unconfirmed.
MAPASGEN — mapasgen.com