SHEMIM / Why scent

We treat smell as a minor sense. Biology disagrees.

The body is saturated with chemistry it both emits and reads, and the more closely we look, the stranger and more central it becomes. These are some of the questions that drive our work. We don't claim to have answered them. We think they're the right questions, and we tag each one honestly for how settled it is.

Open questions

Filled dot — firmer, better-documented evidence. Hollow dot — less settled: inference, mixed evidence, or hypothesis. Every tag says which.

  1. Why do we sniff our own hand after shaking someone else’s?

    Documented

    People do, measurably more after a handshake than before. It looks like covert chemical sampling of the person we just met.

  2. Why do we close our eyes and mouth to kiss?

    Inference

    A close kiss is also a close-range exchange of scent and chemistry. How much of attraction is the nose deciding?

  3. Does perfume erase our natural scent?

    Documented

    Less than we tend to assume. We mostly choose perfumes that blend with our own scent rather than bury it — and in tests, people can still tell individuals apart by body odour even while they are wearing fragrance.

  4. Does our body scent shape attraction?

    Mixed evidence

    Up close — a handshake, a kiss — we sample each other’s scent, often without realising. Whether it steers who we are drawn to is still debated: the popular idea that we “smell” immune-gene compatibility in a partner comes from real studies, but in humans the evidence is mixed and much of it has not replicated.

  5. Why do animals sniff before they mate?

    Documented

    Across species, chemical cues carry information about health and genetic compatibility, assessed before anything else.

  6. Why do women, on average, out-smell men, and have more cells in the olfactory bulb?

    Supported, with caveats

    And why do men emit more of certain putative chemical signals? Sex and smell are wired together more deeply than we assume.

  7. Why does pregnancy sharpen the sense of smell?

    Hypothesis

    Heightened smell, and strong new aversions, are commonly reported in early pregnancy, exactly when the embryo is most sensitive. Is it a protective filter against toxins and spoiled food?

  8. And why the shift in cravings?

    Mixed evidence

    Pregnancy reshapes the gut microbiome, and appetites change with it. What is the body asking for, and why?

  9. Why are olfactory receptors found all over the body?

    Documented

    They are the largest gene family we have — close to a thousand genes — and they are GPCRs, the receptor class about a third of all medicines already target. Built to detect odor molecules, they also turn up far from the nose — skin, gut, even sperm — doing other jobs; one in skin, OR2AT4, helps wounds close and hair grow. Smell may be an ancient, body-wide signaling language.

  10. Why does the body carry scent-receptors before it has a nose?

    Documented

    These receptors are present before the body has a face to wear them. They are switched on in the embryo’s earliest germ cells, and ride on sperm before fertilisation has even happened — already there before the embryonic period (3–8 weeks), before the first bud of a nose, the olfactory placode, has formed. What they are doing there, we leave open. But the order is striking: the receptor comes before the organ.

  11. Why would a kidney need a sense of smell?

    Documented

    Because smelling is only reading molecules — and the body reads its own. A receptor in the kidney, Olfr78, listens for the short-chain fatty acids our gut bacteria release as they digest, and helps tune blood pressure in response. The nose is just the most famous organ doing what many do quietly: taking the measure of the chemistry around them.

  12. Can a scent be a medicine?

    Documented · early

    Sometimes — once we stop meaning perfume by “scent.” The body grew these receptors inside its own organs, not only its nose, so give the right tissue the right molecule and it answers. Switched on in the lab, an odour-receptor on colon-cancer cells slowed their division and tipped them toward dying. In artery walls, the opposite: a receptor that smells a molecule in the blood switches on the inflammation behind heart disease — so there the medicine is to silence it. The receptors are levers; medicine is learning which way to turn each. These are early findings — molecules delivered to tissue, not aromas we inhale.

  13. Does smell read a molecule’s shape, or its chemistry?

    Documented

    More than shape. Some receptors literally need copper to detect sulfur smells — which is why a trace of the odorant added to natural gas registers about a hundred million times more keenly than the matching alcohol. The nose reads a molecule’s chemistry, not just its silhouette.

  14. Does the body announce illness by its scent?

    Documented

    Sometimes plainly. Clinicians are still taught the sweet acetone of a diabetic crisis, the maple-sugar urine of one inherited disorder, the fishy note of another. And newer instruments reach further: Parkinson’s leaves a faint signature in the skin’s oils — found because one woman could smell her husband’s illness years before his diagnosis, and a mass spectrometer later agreed with her nose.

  15. Can a breath be read like a blood test?

    Documented

    In one case, already. Exhaled nitric oxide is measured in clinics every day to gauge airway inflammation and steer treatment — a health signal read straight from the breath. The wider promise is the volatilome: the volatile part of the body’s metabolism, hundreds of molecules carried out on each exhale. Reading the whole of it reliably is still emerging — but that the breath carries the signal is no longer in question.

  16. And what is “cranial nerve zero”?

    Open question

    A small nerve, found after the twelve cranial nerves were already numbered, running from nose to brain and tied to reproductive signaling. We still don’t fully know what it does in humans.

Go deeper — The Molecular Sense: scent as medicine

The thread through all of it

The body is continuously writing chemistry into the air, and continuously reading the chemistry around it. SHEMIM's work is to learn to read that language honestly, and to ask what becomes possible when we can.

An exploratory thread

Where the nose meets awareness.

One thread we hold openly and label clearly as exploratory: the olfactory nerve reaches the brain without first passing through the usual relay station, and if breathing were only about oxygen, the mouth, a far larger airway, would be the main route. Yet we are built to breathe through the nose. Read alongside the old image of the breath of life given through the nostrils, it raises a question worth asking, even if it is far from answered: does olfaction sit closer to awareness than we assume?

This is a research direction, not a result. We keep it distinct from the evidence above on purpose.

If these are your questions too

SHEMIM is built in the open and looking for people who can move specific threads from question to evidence.

Collaborate See the program